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Select this Article		An Efficient and Accurate Method for Calculating the Stochastic Seismic Response of a Non‐Proportionally Damped Structure Wei Guo, Zhi‐wu Yu, and Zhen Guo Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000655 Posted ahead of print 21 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract In the case of non‐proportionally damped structures, the forced decoupling method is often adopted for an approximate analysis. However, it generally cannot satisfy precision requirements for practical engineering. Taking into account this point, methods for calculating the stochastic seismic response of non‐proportionally damped structures are systematically studied in this paper, and based on the pseudo‐excitation method an efficient and accurate iteration method with advantages of high computational efficiency and iteration convergence is also proposed. This new method is preferred for practical engineering because of real expressions. In the end, a numerical example is carried out to verify the properties and advantages of the proposed method.

Select this Article		Shake Table Testing of Slender RC Shear Walls Subjected to Eastern North America Seismic Ground Motions Iman Ghorbanirenani, Robert Tremblay, Pierre Léger, M. ASCE, and Martin Leclerc Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000581 Posted ahead of print 21 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents shake table test results on two identical 1:0.429 scaled, 8‐story moderately ductile reinforced concrete shear wall specimens under high frequency ground motion expected in Eastern North America. The walls were designed and detailed according to the seismic provisions of NBCC 2005 and CSA‐A23.3‐04 standard. The objectives were to validate and understand the inelastic responses and interaction of shear, flexure and axial loads in plastic hinge zones of the walls considering the higher mode effects. One specimen was tested under incremental ground motion intensities ranging from 40% to 120% of the design level. The intensity range was increased from 100% to 200% for the second specimen. The response of the walls was significantly affected by the second mode, causing inelastic flexural response to develop at the base as well as the 6^th level. Dynamic amplification of the base shear forces was also observed in both walls. In the second wall, which was tested in the undamaged condition, peak base shear forces occurred prior to significant inelastic rotation and the contribution to concrete to shear resistance exceeded the value used in design. Once inelastic rotation had developed, that contribution corresponded to the value obtained using a value of 0.18 for the reduction factor accounting for concrete cracking. Inelastic rotation in the upper wall region was found to limit the force demand imposed by higher mode response.

Select this Article		Use of the Wind Tunnel Test Method for Obtaining Design Wind Loads on Roof‐Mounted Solar Arrays Gregory A. Kopp and David Banks Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000654 Posted ahead of print 18 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract ASCE 7 does not provide design wind loads for roof‐mounted solar panels. This technical note discusses the use of the wind tunnel test method, called Method 3 in ASCE 7‐05, which was originally intended for obtaining design wind loads for individual buildings. Since roof‐mounted solar arrays are generally mounted in many configurations, on many buildings, of many different shapes, additional requirements are necessary in order to use Method 3 in this situation. The note describes these additional requirements.

Select this Article		Performance‐Based Seismic Design of Mid‐Rise Woodframe Buildings John W. van de Lindt, M. ASCE, David V. Rosowsky, F. ASCE, Weichiang Pang, M. ASCE, and Shiling Pei, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000653 Posted ahead of print 18 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Our understanding of and ability to predict the seismic behavior of woodframe structures has improved immensely in the last ten years. Two notable projects occurred in succession, the CUREE‐Caltech Woodframe Project and the NEESWood Project, which provided greater understanding, improved analytical modeling, and advances in force‐based and performance based seismic design of woodframe buildings, respectively. The NEESWood project focused on the development of a performance‐based seismic design philosophy (and procedures) for mid‐rise woodframe buildings and included full‐scale system‐level validation. To date, the complete design procedure has not been systematically explained which serves as the impetus for this paper. While the method was shown to be quite viable, some challenges remain including identifying a format that would facilitate widespread adoption and use by engineers. Thus, this paper examines the progress, current state, and challenges for performance‐based seismic design (PBSD) of midrise woodframe buildings.

Select this Article		Buckling, Post‐Buckling, Strength and DSM Design of Cold‐Formed Steel Continuous Lipped Channel Beams Cilmar Basaglia and Dinar Camotim Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000651 Posted ahead of print 18 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract The work reported in this paper is part of an ongoing numerical investigation aimed at (i) assessing the buckling, post‐buckling, strength and collapse behavior of cold‐formed steel continuous beams and simple frames, and (ii) developing an efficient methodology, based on the Direct Strength Method (DSM) approach, to design such structural systems. The results available at this stage concern two and three‐span lipped channel beams subjected to non‐uniform bending and they include the assessment of how accurately the beam ultimate strengths can be predicted by the current DSM design curves. The numerical results presented and discussed are obtained through analyses based on Generalized Beam Theory (elastic buckling analyses) and shell finite element models (all the remaining analyses). Ultimate strength values yielded by geometrically and materially non‐linear shell finite element analyses are compared with estimates provided by the DSM equations and, on the basis of this comparison, it is possible to identify some features that must be included in a DSM approach applicable to continuous cold‐formed steel beams.

Select this Article		Net Section Tension Capacity of Cold‐Reduced Sheet Steel Channel Braces Bolted at the Web Lip H. Teh, A.M.ASCE and Benoit P. Gilbert Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000650 Posted ahead of print 18 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper examines the accuracy of equations specified by the North American and Australasian steel structures codes for determining the net section tension capacity of a channel brace. It points out that there are three distinct factors affecting the net section efficiency of a cold‐formed steel channel brace bolted at the web. These factors are the in‐plane shear lag associated with stress concentration around a bolt hole that is also present in flat sheets, the out‐of‐plane shear lag that is also present in an I‐section bolted at the flanges only, and the bending moment arising from the connection eccentricity with respect to the neutral axis. Each of the relevant factors is explicitly incorporated in the equation proposed in this paper for determining the net section tension capacity of a cold‐formed steel channel brace bolted at the web. The proposed equation is demonstrated through laboratory tests on low ductility channel braces having practical aspect ratios that were bolted onto flexible plates to be more reliable than the code equations and those existing in the literature.

Select this Article		Multiple Points‐In‐Time Estimation of Peak Wind Effects on Structures DongHun Yeo, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000649 Posted ahead of print 18 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract One of the problems encountered in the estimation of wind effects on high‐rise structures is the development of combinations of wind‐induced translational responses in possible conjunction with rotational responses, and/or of forces and moments that contribute to the wind‐induced demand at various cross sections of individual structural members. In current wind engineering practice such combinations are developed in large part intuitively, since phase information on the effects being combined is not readily available from frequency domain analyses. In contrast, full time series analyses can produce estimates of combined wind effects, since they preserve phase information; however, such analyses can be overly time‐consuming. In current wind engineering practice it is common to use the empirical “point‐in‐time” (PIT) procedure for the estimation of peaks of combined stationary stochastic processes. The procedure is applied to pairs of such processes, and consists of adding an estimate of the peak value of one of the processes to the estimated value of the second process at the time of the occurrence of that peak. Even if the full time histories of the two stochastic processes are used, errors inherent in PIT can in some cases as high as 20% on the unconservative side. The purpose of this paper is to present the empirical “multiple points‐in‐time” (MPIT) procedure, which improves significantly upon the PIT. The procedure is illustrated by an application to a 60‐story reinforced concrete structure. Results show that the MPIT approach produces remarkably accurate estimates of the peak combined wind effects by using a limited number of peaks of the time histories of the individual wind effects being combined. Those estimates are obtained far more economically in terms of computational time than conventional time domain estimates that use full time histories.

Select this Article		Simulation‐Based Fragility Relationships for Unreinforced Masonry Buildings Thomas M. Frankie, Bora Gencturk, and Amr S. Elnashai Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000648 Posted ahead of print 18 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Unreinforced masonry (URM) structures represent a significant portion of the residential building stock of the Central and Eastern United States (CEUS). 15% of homes in the 8‐state region impacted by the New‐Madrid Seismic Zone are URM buildings. The brittle nature of URM buildings further supports a thorough consideration of seismic response given the susceptibility to severe failure modes. Currently, there is a pressing need for analytically‐based fragility curves for URM buildings. In order to improve the estimation of damage state probabilities through the development of simulation‐based URM fragilities, an extensive literature survey is conducted on pushover analysis. Using this data, capacity curves are generated, from which damage performance limit states are defined. Demand is simulated using synthetically‐derived accelerograms representative of the CEUS. Structural response is evaluated using an advanced capacity spectrum method. Capacity, demand, and response are thus derived analytically and utilized to generate a more reliable and uniform set of fragility curves for use in loss‐assessment software. This paper presents a framework amenable to rapid, flexible updating that, with the appropriate database of studies, is capable of producing curves representative of any URM building typology subjected to a specified hazard. The curves are expressed in multiple forms to demonstrate capability of use in various loss‐assessment applications.

Select this Article		Internal Pressure in Real Flexible Porous Buildings with a Dominant Opening: A Design Perspective T. K. Guha, R. N. Sharma, and P. J. Richards Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000645 Posted ahead of print 4 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Analytical and associated numerical investigations of the fluctuating internal pressures induced through a dominant opening in real buildings with leaky and flexible envelopes are undertaken. The damping effect of these factors both separately and in combination are quantified using root‐mean‐square (RMS) internal pressure coefficients and equivalent damping ratios for a range of envelope flexibilities and background porosities for the case of the TTU test building and a large‐span industrial building. Simulated ratios of the RMS internal pressures and the peak spectral response of internal pressure for leaky and flexible buildings to that of rigid, nonporous envelopes are presented in non‐dimensional format for a range of building volumes, opening areas and porosity ratios. Additionally non‐dimensional curves of the RMS internal to external pressure ratios for real flexible and leaky envelopes are presented along with experimental data reported in literature in a form suitable for design purpose.

Select this Article		Patching Asymptotics Solution of a Cable with a Small Bending Stiffness Vincent Denoël, Member, ASCE and Thomas Canor Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000643 Posted ahead of print 26 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract The analysis of a cable with a small bending stiffness is a problem encountered in many engineering applications such as the fatigue assessment of stay cables, the modeling of pipeline laying operation or the determination of bending stresses in drillpipe assemblies. Because this phenomenon is modeled by a singularly perturbed equation, standard numerical techniques fail to solve these problems efficiently. As an alternative, provided the complexity of the analytical developments does not preclude their application, these problems may be tackled with appealing analytical procedures such as matching asymptotics or multiple scales. Otherwise advanced numerical simulations combining patching asymptotics within a numerical framework are the only possible approach for problems where the governing equations are too complex. Patching asymptotics also features a number of merits such as the possibility of using a boundary layer with a finite extent. Aiming at a better understanding of this latter technique, it is considered here to determine the solution of a cable with a small bending stiffness. Interesting details about patchability conditions and about how to restore higher derivatives continuity are included. The accuracy of the patching asymptotics approach is also compared with that of matched asymptotics.

Select this Article		Fillet Weld Groups Loaded with out of Plane Eccentricity — Simulations and New Model for Strength Characterization A.M. Kanvinde, J. Liu, X. Fu, and R.J. Cooke Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000641 Posted ahead of print 26 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract The strength of fillet weld groups, loaded with an out of plane eccentricity is controlled by complex interactions of weld yielding as well as bearing between the connected parts. Current models that characterize connection strength, including those used in North American design specifications are highly conservative, leading to oversized welds. These models are phenomenological, because the internal stress distribution within the welds is difficult to characterize experimentally. A new model is proposed for characterizing the strength of these connections. The model is based on insights developed from sophisticated finite element (FE) simulations that feature accurate measurements of weld profiles, multiaxial plasticity and simulation of contact and gapping phenomena that strongly influence connection response. The FE simulations reveal that current models do not reflect key aspects of force transfer within the connection, especially on the compression side. The proposed model incorporates these insights, by using stress profiles and mechanisms consistent with those implied by the FE simulations. The model is evaluated against 79 experiments from three test programs. It is determined that the new model greatly reduces the conservatism of the existing models, resulting in an average test to predicted ratio of 1.01. This is in contrast to previous models, for which the average test‐predicted ratios are in the range of 1.33 to 1.77. The efficacy of the proposed model is analyzed with respect to various parameters, and its limitations are outlined.

Select this Article		Demonstration of Compatible Yielding between Soil‐Foundation and Superstructure Components Weian Liu, Tara C. Hutchinson, Bruce L. Kutter, Manouchehr Hakhamaneshi, Mark Aschheim, and Sashi Kunnath Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000637 Posted ahead of print 26 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Although the nonlinear behavior of rocking shallow foundations has been experimentally and numerically demonstrated as an effective tool to dissipate vibrational energy during seismic loading, the engineering community has yet to uniformly accept it as a targeted design mechanism for diffusing seismic energy in a structure. This paper presents results of a centrifuge test program that incorporated inelastic behaviors into model building systems via yielding of both structural and foundation components. Three two‐story building models were designed with similar layouts but different combinations of foundation and structural component yield strengths and shaken with a similar suite of earthquake motions. Measurements of behavior of each of the model buildings are presented and cross‐compared in terms of time history responses, hysteretic responses of the structural and foundation fuses, and maximum response parameters. The balanced design configuration, wherein the rocking foundation and structural fuses are intended to yield at approximately the same load, is demonstrated to be a well‐controlled seismic‐resistant system, with greatly reduced seismic ductility demand on structural components. Moreover, seismic energy is well distributed amongst the targeted yielding components. If the footing is restrained from rocking, the structural component ductility demand is significantly greater. Another building‐foundation system, in which foundation rocking dominates as opposed to structural hinging, will protect the superstructure from seismic demands. In contrast, when the rocking foundation capacity is more than twice that of the structural fuses, rotations at the foundations are reduced significantly, at the price of much larger demands to the superstructure.

Select this Article		Cyclic Seismic Testing of Composite Concrete‐Filled U‐shape Steel Beam‐to‐H Column Connections Cheol‐Ho Lee, M. ASCE, Hong‐Gun Park, M. ASCE, Chang‐Hee Park, Hyeon‐Jong Hwang, Chang‐Nam Lee, Hyoung‐Seop Kim, and Sung‐Bae Kim Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000635 Posted ahead of print 26 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract In this study, cyclic seismic performance of concrete‐filled U‐shape steel beam to H‐shape steel column connections was experimentally evaluated. The concrete‐filled U‐shape steel beams were compositely attached to the concrete floor slab. Test was conducted in two stages. The first testing program was carried out on one‐sided moment connections to find the most promising connecting scheme. The strengthening scheme, or welding steel plates to the beam bottom flange with minimized stress concentration, was shown to be the most satisfactory and it was used in the second‐stage test on two full‐scale cruciform specimens. Considering the unique constructional nature of the proposed composite connections, the critical limit states such as weld fracture, local buckling, concrete crushing, and rebar buckling were carefully addressed in designing specimens. Test results showed that the connection details and design procedures proposed in this study can successfully control the critical limit states mentioned above. The proposed connection detail successfully pushed the plastic hinging to the tip of the strengthened zone as intended in design, thus effectively protecting the more vulnerable beam to column welded joint. The specimens typically exhibited a maximum story drift capacity of over 5.5% radians, exceeding the minimum limit of 4% radians required of special moment frames. Four out of the five specimens tested in this study eventually failed by the low‐cycle fatigue fracture across the beam bottom flange at high story drift over 5.0% radians.

Select this Article		Severely Corroded Reinforced Concrete with Cover Cracking Dario Coronelli, Kamyab Zandi Hanjari, and Karin Lundgren Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000633 Posted ahead of print 26 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract In many corroding RC structures, it is not uncommon that cover cracking, spalling and delamination have occurred. Previous research has mainly been concerned with corrosion levels leading to cover cracking along the main reinforcement, while corrosion of stirrups is often overlooked. Corrosion phenomena including stirrup corrosion were studied in an experimental investigation presented in this paper. High levels of corrosion were reached, up to 20% of the main bars and 34% of the stirrups legs. The occurrence of crack initiation, propagation and cover delamination were examined. The specimens had the shape of a beam end and were corroded with accelerated method; an imposed current was used, taking care to keep the current density as low as practically possible for the duration of the laboratory testing. The effects of this process are compared with those of natural corrosion using models from the literature. The location of the bar, middle and corner placement, the amount of transverse reinforcement and the corrosion level of longitudinal reinforcement and of transverse reinforcement were studied. The results concerning the concrete cracking in the experimental campaign are presented here. The crack patterns and widths are analysed, showing differences between specimens with or without stirrups and when stirrups are corroding or not. Finally, the effect of corrosion was simulated as the expansion of corrosion products in a finite element model, and the results, mainly the crack pattern and width, are compared with the test results. The conclusions address the importance of taking into consideration both high corrosion levels and corrosion of stirrups for the assessment of deteriorated structures.

Select this Article		Simplified Optimum Design Procedure for Special Unbonded Post‐Tensioned Split Precast Shear Walls R.A. Hawileh, E.I Saqan, and J.A. Abdalla Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000631 Posted ahead of print 26 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract In this paper a set of simplified design equations for unbonded post‐tensioned (PT) precast split hybrid shear wall system is developed. Such a system was proposed by the Precast Seismic Structural Systems (PRESSS) and can be used as a bearing wall or a special reinforced concrete wall for building frames, as defined in ASCE/SEI 7, for eliminating residual drift after seismic events. The panels are anchored to the foundation with unbonded PT tendons located at panel center; adjacent panels are connected with uniformly distributed energy dissipating coupling devices. An iterative design procedure to calculate the required area of the PT reinforcement and the total yield force of all shear connectors in one vertical joint was proposed by PRESSS. This iterative procedure is exact but tedious and lengthy. A simpler non‐dimensional chart‐based design procedure was proposed by the Authors. This procedure is efficient but has limitations. A non‐iterative procedure adopted by ACI ITG‐5.2, although simple, does not yield the optimum combination of the shear connectors force and PT force. The set of simplified design equations proposed in this study overcomes the shortcomings of these three procedures. It is simple, direct (non‐iterative), general and yields the optimum design in fewer number of steps. The proposed design equations predicted values are accurate and are normally within ±2% of the exact optimum solution.

Select this Article		Effectiveness of Tuned Mass Dampers Against Ground Motion Pulses E. Matta, Ph.D., P.E. Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000629 Posted ahead of print 26 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract It is known that the effectiveness of tuned mass dampers (TMDs) decreases as the input duration shortens. As a result, their use is commonly discouraged against short‐duration, pulse‐like ground motions, such as those occurring in near‐field (NF) zones in the presence of forward‐directivity or fling‐step effects. Yet a systematic assessment of such control impairment is still missing. In this paper, a recent analytical model of ground motion pulses is applied to the design and evaluation of TMDs against impulsive earthquakes. Based on this model, first a new optimization method is introduced as an alternative to the classical H_∞ approach. Then the two strategies are tested on single‐ and multi‐ degrees‐of‐freedom linear structures subject both to analytical pulses and to a large set of NF records possessing pulse‐like features. The resulting statistical evaluation, expressed by percentile response spectra, shows the pros and cons of a pulse‐oriented TMD design, and improves the general understanding of TMDs performance under impulsive ground motions.

Select this Article		Experimental Seismic Performance of Beam‐Column Subassemblies Using Ductile Embeds Barbara Chang, Tara C. Hutchinson, M. ASCE, Xiang Wang, and Robert Englekirk Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000628 Posted ahead of print 12 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Based on current special moment frame design requirements, conventional reinforced concrete beam‐column joints in frame‐braced buildings designed to resist seismic loads suffer severe damage when plastic hinging is taken to design limits. Construction of these conventional beam‐column joints is also costly and labor intensive. In this paper, we summarize the full‐scale experimental behavior of two alternative subsystems incorporating ductile embeds. Observations from the experiments indicate that both specimens exhibit stable hysteretic behavior with no strength degradation in excess of 7% drift ratio. At design plastic rotations expected of conventional beam‐column joints, no joint spalling and only minor damage along beam members was observed. A design‐oriented lumped element model is described, which reasonably captures the local behavior of the specimens.

Select this Article		Seismic Response of Single‐Degree‐of‐Freedom Systems Representing Low‐Ductility Steel Concentrically‐Braced Frames with Reserve Capacity Gang Li and Larry A. Fahnestock, P.E., M.ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000623 Posted ahead of print 11 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Steel concentrically braced frames (CBFs) are used widely as a seismic lateral force resisting system. Although modern CBFs designed for high seismic regions have considerable ductility, CBFs in moderate seismic regions are expected to have limited ductility, even when designed using modern provisions. In addition, older CBFs in high seismic regions also are expected to have limited ductility. In these low‐ductility systems, reserve capacity (i.e. secondary strength and stiffness) plays an important role in seismic collapse prevention. Thus, quantifying the impact of reserve capacity on earthquake response for low‐ductility systems is critical. This paper presents research that used single‐degree‐of‐freedom systems to represent low‐ductility CBFs, where brace fracture causes a sudden loss of strength and stiffness. Post brace fracture stability was studied by considering variations in reserve system strength and stiffness parameters. Performance was evaluated by considering local ductility demands on the reserve system and global drift demands. For the cases considered, ductility capacity of the reserve system was typically a more critical constraint than global drift capacity. Reserve capacity is demonstrated to appreciably influence seismic collapse behavior, whereas primary system strength has a small influence.

Select this Article		A Dual‐Objective‐Based Tornado Design Philosophy John W. van de Lindt, M. ASCE, Shiling Pei, M. ASCE, Thang Dao, A.M. ASCE, Andrew Graettinger, M. ASCE, David O. Prevatt, M. ASCE, Rakesh Gupta, M. ASCE, and William Coulbourne, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000622 Posted ahead of print 14 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Tornadoes represent a unique natural hazard because of the very low probability of occurrence, short warning times (on the order of only a few minutes), and the intense and destructive forces imposed on engineered and non‐engineered buildings. The very low‐probability very high‐consequence nature of a tornado strike makes designing for survival and reducing damage under typical financial constraints a substantial challenge. On April 27, 2011 an EF4 tornado devastated a 0.8 km (1/2 mile) wide path almost 10 km (5.9 miles) long through the city of Tuscaloosa, Alabama continuing on the ground for 130 km (80 miles). This paper presents the design concept that resulted following a week‐long data reconnaissance deployment throughout the city of Tuscaloosa by the authors. The dual‐objective philosophy proposed herein is intended to focus on both building damage and loss reduction in low to moderate tornado windspeeds and building occupant life safety in more damaging wind speed events such as EF4 and EF5 tornadoes. The philosophy articulates a design methodology that is the basis upon which structural engineering was formed, namely provide life safety and control damage, but focused at separate tornado intensity levels.

Select this Article		Time‐frequency Blind Source Separation using Independent Component Analysis for Output‐only Modal Identification of Highly‐damped Structures Yongchao Yang and Satish Nagarajaiah Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000621 Posted ahead of print 11 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Output‐only algorithms are needed for modal identification when only structural responses are available. The recent years have witnessed fast development of blind source separation (BSS) as a promising signal processing technique, pursuing to recover the sources using only the measured mixtures. As the most popular tool solving the BSS problem, independent component analysis (ICA) is able to directly extract the time‐domain modal responses, which are viewed as virtual sources, from the observed system responses; however, it has been shown that ICA loses accuracy in the presence of higher level of damping. In this study, the modal identification issue which is incorporated into the BSS formulation is transformed into a time‐frequency framework. The sparse time‐frequency representations of the monotone modal responses are proposed as the targeted independent sources hidden in those of the system responses which have been short‐time‐Fourier‐transformed (STFT); they can then be efficiently extracted by ICA, whereby the time‐domain modal responses are recovered such that the modal parameters are readily obtained. Simulation results of a multi‐degree‐of‐freedom (MDOF) system illustrate that the proposed output‐only STFT‐ICA method is capable of accurately identifying modal information of lightly‐ and highly‐ damped structures, even in the presence of heavy noise and non‐stationary excitation. The laboratory experiment on a highly‐damped three‐story frame and the analysis of the real‐measured seismic responses of the USC hospital building demonstrate the capability of the method to perform “blind” modal identification in practical applications.

Select this Article		An Investigation on the Design of Steel Storage Rack Columns via the Direct Strength Method Miquel Casafont, Maria Magdalena Pastor, Francesc Roure, Jordi Bonada, and Teoman Peköz Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000620 Posted ahead of print 11 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract The paper presents an attempt to predict the load carrying capacity of perforated rack columns by means of the Direct Strength Method (DSM). The investigation is focused on two different issues: the prediction of the elastic buckling loads of members with multiple perforations, and the evaluation of the accuracy of the current DSM buckling curves when applied to rack columns. In relation to the first issue, a model for the calculation of the reduced thickness of the perforated strip to be used in finite strip buckling analysis is developed. Regarding the study of the DSM curves, it is demonstrated that they can be used to accurately determine the strength of rack cross‐sections whose failure is governed by distortional buckling or global buckling (with no significant participation of local buckling). This is an interesting result because it will allow substituting the distortional buckling tests, that are currently carried out in the process of design of these columns, by a simple and easy to apply calculation procedure.

Select this Article		Structural Behavior of Symmetric Spindle‐Shaped Tensairity Girders Rolf H. Luchsinger and Cédric Galliot Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000619 Posted ahead of print 11 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract The load bearing behavior of a symmetric spindle‐shaped Tensairity girder with 5 m span and thin chords is studied experimentally, numerically and analytically. The influence of the air pressure on the load‐deflection behavior is investigated for homogeneous distributed load, asymmetric distributed load and central local load. An m‐shaped deflection with two maxima at about one and three quarter of the span was obtained for homogeneous distributed loads whose distribution is not linearly dependent on the applied load. The slope of the load‐deflection curve as well as the maximal load increases with increasing air pressure demonstrating the stabilizing role of the inflated hull. An analytical model based on two beams coupled by an elastic foundation with air pressure dependent properties is presented for the homogeneous distributed load case and simple predictions for the average displacement and the maximal load are given. The model reveals the subtle interplay between the chords and the inflated hull leading to the peculiar displacement distribution of the system. Finite element analysis shows the limiting influence of the low fabric shear modulus on the stiffness and load bearing capacity of the Tensairity girder for local and asymmetric distributed load. The investigated spindle‐shaped Tensairity girder is optimal for homogeneous distributed loads, where a live load to dead load ratio of more than 50 has been achieved.

Select this Article		Performance of Steel Moment Connections under a Column Removal Scenario. I: Experiments H. S. Lew, Ph.D., P.E., F.ASCE, Joseph A. Main, Ph.D., A.M.ASCE, Stephen D. Robert, A.M.ASCE, Fahim Sadek, Ph.D., M.ASCE, and Vincent P. Chiarito, P.E., M.ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000618 Posted ahead of print 3 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents an experimental study of two full‐scale steel beam‐column assemblies, each comprising three columns and two beams, to (1) define their response characteristics under a column removal scenario, including the capacity of the beams and their connections to carry loads through catenary action, and (2) provide experimental data for validation of beam‐to‐column connection models for assessing the robustness of structural systems. The assemblies represent portions of the exterior moment‐resisting frames of two ten‐story steel frame buildings. One test specimen had welded unreinforced flange, bolted web connections, and the other had reduced beam section connections. When subjected to monotonically increasing vertical displacement of the unsupported center column, both specimens exhibited an initial elastic response dominated by flexure. With increased vertical displacement, the connections yielded, and axial tension developed in the beams. The axial tension in the beams increased until the connections failed under combined bending and axial stresses. The test results show that the rotational capacities of both connections under monotonic column displacement are about twice as large as those based on seismic test data.

Select this Article		Performance of Steel Moment Connections under a Column Removal Scenario. II: Analysis Fahim Sadek, Ph.D., M.ASCE, Joseph A. Main, Ph.D., M.ASCE, H. S. Lew, Ph.D., P.E., F.ASCE, and Sherif El‐Tawil, Ph.D., P.E., F.ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000617 Posted ahead of print 3 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a computational investigation of the response of steel beam‐column assemblies with moment connections under monotonic loading conditions simulating a column removal scenario. Two beam‐column assemblies are analyzed, which incorporate (1) welded unreinforced flange, bolted web connections and (2) reduced beam section connections. Detailed models of the assemblies are developed, which use highly refined solid and shell elements to represent nonlinear material behavior and fracture. Reduced models are also developed, which use a much smaller number of beam and spring elements and are intended for use in future studies to assess the vulnerability of complete structural systems to disproportionate collapse. The two modeling approaches are described, and computational results are compared with the results of full‐scale tests described in the companion paper. Good agreement is observed, demonstrating that both the detailed and reduced models are capable of capturing the predominant response characteristics and failure modes of the assemblies, including the development of tensile forces associated with catenary action and the ultimate failure of the moment connections under combined bending and axial stresses.

Select this Article		Negative Stiffness Device for Seismic Protection of Structures A. A. Sarlis, D. T. R. Pasala, S.M.ASCE, M. C. Constantinou, M.ASCE, A. M. Reinhorn, F.ASCE, S. Nagarajaiah, M.ASCE, and D. P. Taylor Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000616 Posted ahead of print 11 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Structural weakening and addition of damping is an approach previously proposed for the reduction of seismic forces and drifts in the retrofit of structures. It is also used in the design of new buildings with damping systems. While this approach is efficient, it does not significantly reduce and may even amplify inelastic excursions and permanent deformations of the structural system during a seismic event. This paper describes a negative stiffness device (NSD) that can emulate weakening of the structural system without inelastic excursions and permanent deformations. The NSD simulates yielding by engaging at a prescribed displacement and by applying a force at its installation level that opposes the structural restoring force. The NSD consists of (a) a self contained highly compressed spring in a double negative stiffness magnification mechanism and (b) a “gap spring assembly” (GSA) mechanism which delays the engagement of negative stiffness until the structural system undergoes a prescribed displacement. The NSD employs double chevron braces that self‐contain the large vertical forces needed for the development of the horizontal negative stiffness without transferring these forces to the structure. This paper reports the development and operation of the NSD and presents analytical and computational tools that describe the behavior of the device. The principles of global control of structures using the NSD are presented in a companion paper. Additional papers present results of testing of the device, and results of analytical and experimental studies on the application of the device in a 3‐story conventional structure and a 3‐story seismically isolated structure.

Select this Article		Adaptive Negative Stiffness: A New Structural Modification Approach for Seismic Protection D. T. R. Pasala, S.M.ASCE, A. A. Sarlis, S.M.ASCE, S. Nagarajaiah, M.ASCE, A. M. Reinhorn, F.ASCE, M. C. Constantinou, M.ASCE, and D. Taylor, M.ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000615 Posted ahead of print 3 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Yielding can be emulated in a structural system by adding an adaptive "negative stiffness device" (NSD) and shifting the "yielding" away from the main structural system‐leading to the new idea of "apparent weakening" that occurs ensuring structural stability at all displacement amplitudes. This is achieved through an adaptive negative stiffness system (ANSS), a combination of NSD and a viscous damper. By engaging the NSD at an appropriate displacement (apparent yield displacement that is well below the actual yield displacement of the structural system) the composite structure‐device assembly behaves like a yielding structure. The combined NSD‐structure system presented in this study has a re‐centering mechanism thereby avoids permanent deformation in the composite structure‐device assembly unless, the main structure itself yields. Essentially, a yielding‐structure is "mimicked" without any, or with minimal permanent deformation or yielding in the main structure. As a result, the main structural system suffers less accelerations, less displacements and less base shear, while the ANSS "absorbs" them. This paper presents comprehensive details on development and study of the ANSS/NSD. Through numerical simulations, the effectiveness and the superior performance of the ANSS/NSD as compared to a structural system with supplemental passive dampers is presented. A companion paper presents the NSD and its mechanics in detail.

Select this Article		Comparative Study on Steel Plate Shear Walls Used in High‐Rise Building Jianguo Nie, Jiansheng Fan, Xiaogang Liu, and Yuan Huang Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000613 Posted ahead of print 3 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Tianjin Jinta Tower is the first high‐rise building built with steel plate shear wall in China. The main lateral force resisting system is the composite core tube composed of steel plate shear walls and concrete filled steel tubular columns. In order to investigate the seismic performance of this structural system and to provide design instructions, two specimens of 2‐bay and 5‐storey steel plate shear walls were tested under low‐cycle reverse loading. The unstiffened steel plates of the first specimen were connected to the boundary beam and column frame by high‐strength bolts. The steel plates of the second specimen were connected to the boundary frame by welding, and the steel panels were stiffened by channels. Both specimens showed satisfactory energy dissipation mechanism during the loading process. For the unstiffened specimen with bolted connections, the considerable post buckling strength generated excellent ductility and energy dissipation performance, but slip at bolted connections and the buckling of steel panels decreased the stiffness in the serviceability condition. The stiffened and welded specimen showed higher stiffness in elastic range and excellent energy dissipation capacity, but the cost of stiffeners would decrease the economy of the steel plate shear walls.

Select this Article		Analysis of Elastic, Doubly Symmetric, Horizontally Curved Beams During Lifting Raymond H. Plaut, M.ASCE and Cristopher D. Moen, M.ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000612 Posted ahead of print 3 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract The lifting of horizontally curved beams (or almost‐straight beams with an imperfection in shape) is considered, with application in the construction of bridges. A circularly curved beam that is suspended at two symmetric locations by vertical or inclined cables is analyzed. The cross section of the beam is assumed to be doubly symmetric, the material is assumed to be linearly elastic, the cross‐sectional dimensions are assumed to be small relative to the radius of curvature, and the deformations are assumed to be small. Both uniform (St. Venant) torsion and inclusion of nonuniform (warping) torsion are treated. Analytical equations are derived for the overall roll angle of the beam, the internal forces and moments, the weak‐axis and strong‐axis deflections, and the cross‐sectional angle of twist. The behavior depends crucially on the locations of the lift points.

Select this Article		Performance of Advanced Materials during Earthquake Loading Tests of a Bridge System Carlos A. Cruz Noguez and M. Saiid Saiidi, FASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000611 Posted ahead of print 3 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Three unconventional details for the plastic hinge regions of bridge columns subjected to seismic loads were developed, designed, and implemented in a large‐scale, four‐span reinforced concrete bridge. Super elastic shape memory alloys (SMA), engineered cementitious composites (ECC), post‐tensioned columns, and elastomeric bearings were used in three different piers to improve the seismic performance of the bridge in terms of minimizing damage and reducing residual displacements. The bridge model was subjected to a series of biaxial earthquake excitations with increasing amplitudes. The experimental results showed that, besides being effective in reducing permanent displacement of the bridge, the high‐performance materials and details substantially reduced the damage at plastic hinge regions and modified significantly other response parameters of the bents compared to conventional reinforced‐concrete (RC) construction. Higher ductility was observed in the pier with SMA/ECC combination and larger load capacity was exhibited by the pier with elastomeric pads. While rotations at the plastic hinges with high performance materials were significantly larger than those measured at plastic hinges made of conventional RC, the measured residual strains in the longitudinal reinforcement in the plastic hinges with innovative details were smaller than those observed in RC plastic hinges.

Select this Article		Estimating natural periods of steel plate shear wall frames Shi Liu, Gordon P. Warn, A.M.ASCE, and Jeffrey W. Berman, A.M.ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000610 Posted ahead of print 10 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract A steel plate shear wall with thin, unstiffened, web plates is one type of seismic lateral force resisting system that is gaining popularity. Steel plate shear walls are utilized in low to mid‐rise building construction typically with two or more frames in each orthogonal direction to resist seismic loading combine with gravity framing. The steel plate shear walls therefore controls the lateral force response of the building and the building's natural periods of vibration. For design of any seismic load resisting system, an estimation of the building's first mode period is necessary to calculate seismic loads and estimate resulting frame drift. This paper presents a method for estimating the first three natural periods of a steel plate shear wall with non‐uniform properties along its height accounting for both shear and flexural deformations of the system. The proposed method approximates the steel plate shear wall frame as shear and flexural systems separately to determine corresponding frequencies then combines these frequencies using Dunkerley's equation. A comparison of periods estimated using the approximate method with those obtained from modal analysis of detailed finite element models suggest that the proposed method is appropriate for estimating the first mode period of SPSW frames. The proposed method could be valuable for refining the seismic design of these frames or for verifying the results of large, complex, steel plate shear wall building models.

Select this Article		Internet‐Enabled Wireless Structural Monitoring Systems: Development and Permanent Deployment at the New Carquinez Suspension Bridge M. Kurata, J. Kim, J. P. Lynch, G. W. van der Linden, H. Sedarat, E. Thometz, P. Hipley, and L. ‐H. Sheng Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000609 Posted ahead of print 12 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Dense networks of low‐cost wireless sensors have the potential to facilitate prolific data collection in large and complex infrastructure at costs lower than those historically associated with tethered counterparts. While wireless telemetry has been previously proposed for structural monitoring, comparatively less research has focused on the creation of a complete and scalable data management system that manages the storage and interrogation of wireless sensor data. This paper reports on the development of a novel wireless structural monitoring system specifically tailored for large‐scale civil infrastructure systems by architecturally combining dense wireless sensor networks with a suite of information technologies remotely accessible by the Internet. The architectural overview of the proposed Internet‐enabled wireless structural monitoring system is presented including a description of its functional elements (for example, wireless sensors, database server and 25 application programming interfaces). The monitoring system architecture proposed is validated on the New Carquinez (Alfred Zampa Memorial) Bridge in Vallejo, CA. A permanent wireless monitoring system is installed consisting of 28 wireless sensor nodes collecting data from over 80 channels. The bridge sensor data is transferred by a wireless cellular connection to a remote database server where it is stored and available for interrogation by software clients granted access to the data. To illustrate the ability to autonomously process the bridge response data, stochastic subspace identification method is used to extract accurate modal characteristics of the bridge that are used to update high‐fidelity finite element models of the bridge. The Internet‐enabled wireless structural monitoring system proved to be scalable to a large number of nodes and has thus far proven stable and reliable over long‐term use.

Select this Article		Collapse Assessment of Steel Moment Frames based on E‐Defense Full‐Scale Shake Table Collapse Tests Dimitrios G. Lignos, A.M.ASCE, Tsuyoshi Hikino, Yuichi Matsuoka, and Masayoshi Nakashima, M.ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000608 Posted ahead of print 10 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents key parameters that affect numerical modeling of steel frame structures for reliable collapse simulations. The collapse assessment is based on experimental data obtained from a full‐scale shaking table collapse test of a four‐story steel moment frame and a blind numerical analysis contest that was organized in parallel with the collapse test. It is demonstrated that (1) there is no clear advantage between 3‐D and 2‐D analyses in the prediction of a sidesway collapse mechanism for buildings with a regular plan view as in the case of study; (2) the assumption of Rayleigh damping leads to better predictions of structural response compared to stiffness proportional damping; and (3) accurate prediction of collapse necessitates that P‐Delta effects always to be considered in the analysis. It is also proven that accurate simulation of steel component deterioration is a key factor for reliable prediction of collapse behavior. Based on a synthesis of experimental and analytical studies, a few collapse mitigation alternatives are investigated. In particular, the effects of the strong‐column/weak‐beam ratio and exposed base plates on the collapse capacity are assessed. It is notable that a combination of bending strength increase and delay of local buckling in first story columns is most effective for the enhancement of seismic performance against collapse.

Select this Article		Torsional responses under bi‐directional seismic excitations: Effect of instantaneous load eccentricities H.P. Hong Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000607 Posted ahead of print 10 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Torsional response for one‐way or two‐way asymmetric linear/nonlinear structural systems under uni‐ and bi‐directional seismic excitations increases the maximum displacement demand on structural systems. In this study, we consider instantaneous load eccentricities caused by the motion of the center of mass. The eccentricities, which are time‐dependent, exist even for linear elastic two‐way symmetric structures under seismic excitations as the relative displacement between the center of mass and center of stiffness may not necessarily be negligible. The quantification of this second order effect on structural response is not available in the literature. Equations are developed and some numerical results are obtained by incorporating this second order effect for linear elastic structures under bi‐directional excitations to quantify the importance of this phenomenon. The results obtained by considering more than 100 ground motion records suggest that, on average, an underestimation of seismic displacement demand can occur if this second order effect is ignored, especially for twoway symmetrical systems. The degree of underestimation depends on the dynamic characteristics of the system, and the record.

Select this Article		Model‐Based Feedforward‐Feedback Actuator Control for Real‐Time Hybrid Simulation Brian M. Phillips and Billie F. Spencer, Jr., F. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000606 Posted ahead of print 6 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Substructure hybrid simulation is a powerful, cost‐effective alternative for testing structural systems, closely coupling numerical simulation and experimental testing to obtain the complete response of a structure. In this approach, well‐understood components of the structure are modeled numerically, while the components of interest are tested physically. Generally, an arbitrary amount of time may be used to calculate and apply displacements at each step of the hybrid simulation. However, when the rate‐dependent behavior of the physical specimen is important, real‐time hybrid simulation (RTHS) must be employed. Computation, communication, and servo‐hydraulic actuator limitations cause delays and lags which lead to inaccuracies and potential instabilities in RTHS. This paper proposes a new model‐based servo‐hydraulic tracking control method including feedforward‐feedback links to achieve accurate tracking of a desired displacement in real‐time. The efficacy of the proposed approach is demonstrated through RTHS of both a single‐degree‐of‐freedom (SDOF) system and a nine‐story steel building, each employing a 200 kN large‐scale magnetorheological damper as the rate‐dependent physical specimen.

Select this Article		A Proposal to Account for Concrete Shrinkage and Environmental Strains in Design of Timber‐Concrete Composite Beams Massimo Fragiacomo and Jörg Schänzlin Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000605 Posted ahead of print 6 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Timber‐concrete composite beams are statically indeterminate structures where a concrete topping is connected via shear connectors to a timber beam. Since effects like drying shrinkage of concrete, variations of timber moisture content and environmental temperature cannot freely occur, self‐equilibrated stresses (eigenstresses) and additional deflection are induced in the composite beam and may reduce the structural safety at ultimate and serviceability limit states, respectively. The paper presents a simplified design approach suitable for implementation in codes of practice to account for these effects, which are all transformed into uniformly distributed loads to be combined with gravity load. The moisture content variations to consider in design are tabled based on climatic region, size of the timber section, type of exposure and protective coating, and may become significant particularly for the deflection of composite beams with narrow timber sections exposed to outdoor, sheltered conditions. Environmental variations and drying shrinkage of concrete are quite influential on the design particularly when this is governed by deflection control at serviceability limit state. Composite beams with solid timber slabs and stiff connection, and composite beams with narrow timber section exposed to outdoor conditions were found to be particularly sensitive to these environmental effects.

Select this Article		Structural Behaviour of CHS T‐Joints Subjected to Brace Axial Compression in Fire Condition K. H. Tan, T. C. Fung, and M. P. Nguyen Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000604 Posted ahead of print 6 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract The structural behaviour of Circular Hollow Section (CHS) T‐joints subjected to axial brace compression in fire conditions was investigated. Five full‐scale tubular joints with different brace‐to‐chord diameter ratios were tested under elevated temperature. The tests were in isothermal heating condition where the specimens were heated to the desired temperatures and then subjected to static load to failure. The ultimate strength and failure modes of these joints were investigated. It was observed that both the reduction in material strength and changes in localized plastification area beneath the brace decreased the ultimate strength of the joints as temperature increased. Furthermore, local buckling and ovalisation of the chords were found to be more concentrated around the joint region at elevated temperature. To the authors' best knowledge, these tests were among the first reported experimental investigations in the ultimate strength and failure mechanisms of tubular joints at elevated temperature. To investigate the joint behaviour at high temperature in greater detail, finite element method was used. The finite element models were first validated by the test results. The development of failure mechanisms of CHS T‐joints at elevated temperature was then traced with the numerical models. The models were also used to quantify the effect of elevated temperatures on three parameters which directly affect the ultimate strength of the T‐joints. The three parameters are boundary condition, pre‐compression in the chord, and chord thickness.

Select this Article		Dynamic Response of Composite Beams with Partial Shear Interaction Using a Higher Order Beam Theory A. Chakrabarti, A. H. Sheikh, M. Griffith, and D. J. Oehlers Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000603 Posted ahead of print 6 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Dynamic response of composite beams with partial interaction is presented using a one dimensional finite element model based on a higher order beam theory. The proposed model takes into account the effect of partial shear interaction between the adjacent layers as well as transverse shear deformation of the beam. A third order variation of the axial displacement of the fibres over the beam depth is taken to have a parabolic variation of shear stress which vanishes at both top and bottom fibres of the transverse composite surface, as clearly derives on free and tangentially unloaded surface of continua. In the proposed FE model, there is no need to incorporate any shear correction factor and the model is free from shear locking problem. The proposed numerical model is validated by comparing the results with those available in literature. Many new results are presented as there is no published result on vibration and buckling of composite beams based on higher order beam theory.

Select this Article		Evaluation of Fatigue Bond Strength of Anchorage Zones with a Mechanical Model Carlos Zanuy, Luis Albajar, and Pablo de la Fuente Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000602 Posted ahead of print 6 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract The paper describes a numerical model to analyze the fatigue behaviour of reinforced concrete anchorage zones. The model takes into account the cycle‐dependent bond‐slip behaviour at the steel‐concrete interface and is able to reproduce the experimental increase of the relative slip developed with number of load cycles, as well as the process of redistribution of stresses that takes place over the anchorage length due to the fatigue damage. The results compare satisfactorily with existing experimental results. The model has been used to derive S‐N curves to provide the fatigue strength of anchorage zones under different confinement conditions and various values of the anchorage length‐to‐diameter ratio and the steel diameter. The results indicate that the confinement degree plays a significant role in the fatigue bond strength: no fatigue problems are found for well‐confined concrete condition, but significantly short fatigue strength is obtained under the moderately confined and unconfined concrete conditions.

Select this Article		Structural Identification for Performance Prediction Considering Uncertainties: A Case Study of a Movable Bridge Hasan Burak Gokce, F. Necati Catbas, M. ASCE, Mustafa Gul, and Dan M. Frangopol, Dist. M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000601 Posted ahead of print 6 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Structural Identification (St‐Id) can simply be described as estimating the structural system properties based on the correlation of inputs and outputs for decision‐making. For a complete St‐Id process, establishing the decision making needs, developing analytical and numerical models, conducting field measurements along with parameter identification using the experimental data for model calibration are carried out. One important consideration is the evaluation of the limitations and the adequacy of using a single calibrated model before leveraging it for decision‐making such as the reliability of the structural system for the remainder of its design life. The uncertainties in the data collected by means of intermittent testing or monitoring, limitations of the models and non‐stationary nature of structural behavior need to be considered. These uncertainties can be incorporated by use of a family of parent and off‐spring models. The objective of this paper is to illustrate the use of family of models that incorporates the uncertainties and make predictions in terms of load rating and system‐level reliability with the help of Structural Health Monitoring (SHM) data. First, the FEM of the movable bridge is calibrated with the SHM data and the parent FEMs are created to best represent the measurements. At the same time, uncertainties in critical structural parameters such as boundary conditions are considered by the off‐spring models. The family of models approach is employed to estimate the load rating and system reliability by considering the probability of failure of the system with different correlations among the safety margins of the components. Finally, future performance of the movable bridge in the case of damage and deterioration is estimated for demonstration of structural identification for performance prediction by considering uncertainties. Such results are expected to provide a set of solutions for the performance of a structure for optimum decision‐making.

Select this Article		Response Spectral Characteristics and Reliabilities of Linear Structures to Both Intensity and Frequency Content Time‐Varying Earthquake Loads Jun He Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000600 Posted ahead of print 6 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract A numerical method for estimating the useful spectral characteristics of responses of classically damped linear elastic structures to the Yeh‐Wen model of fully nonstationary random earthquake loads is developed. The derivation of the method is carried out by three steps. First, the stationary Gaussian white noise process in the space of a frequency modulation function is transformed to the uniformly modulated Gaussian white noise process in the time space. Secondly, the numerical computation procedure for the unit impulse response functions in the time domain of the Clough‐Penzien filters modified in the space of a frequency modulation function is proposed. Finally, the numerical solutions for the useful spectral characteristics of responses of linear structures to the Yeh‐Wen model are given out, from which the first‐passage reliability problem can be solved by using of Vanmarcke's approximation. Numerical investigation of a simple oscillator shows the effect of the frequency modulation functions on the numerical results and computational efficiency of the developed method. The numerical analysis of the spectral characteristics and first‐passage probabilities of a response of a super‐tall TV Tower demonstrates how to implement the numerical method to practical applications.

Select this Article		Precast Concrete Diaphragm Connector Performance Database R. Ren, Ph.D., S. M. ASCE and C. J. Naito, Ph.D., P.E., M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000598 Posted ahead of print 6 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract A variety of connector details are used for providing integrity and force transfer between precast concrete panels in building floor diaphragms. To assess the adequacy of these connectors a large number of experiments have been conducted on discrete welded connectors used in precast concrete double‐tee floor panels. A standard procedure for developing simplified response curves from original test data is used to generate simplified curves from each of the tests conducted. The calculated results of over 200 experiments are summarized in a comprehensive performance database. This database provides stiffness, strength and deformation properties of each connector detail examined. The connectors are divided into one of three displacement based categories: low deformation element (LDE), moderate deformation element (MDE) or high deformation element (HDE) based on the performance measured in the experiments. A simplified pushover modeling approach is developed to estimate the in‐plane maximum midspan flexural deflection and shear sliding of a diaphragm subjected to a static uniform load applied parallel to the span of diaphragm system. This method begins with developing shape functions of joint moment‐rotation and shear‐sliding deformation responses by utilizing the information included in the performance database, and then estimate the in‐plane flexural and shear resistance‐displacement responses of the diaphragm system. Estimation of flexural and shear responses of diaphragm designed with connectors in LDE, MDE and HDE categories are conducted as examples.

Select this Article		Structural Behavior of Corroded Steel Pipes Subject to Axial Compression and Internal Pressure‐ An Experimental Study Halima Dewanbabee and Sreekanta Das Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000596 Posted ahead of print 5 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract External corrosion is found in many onshore oil and gas pipelines and corrosion is a major cause of structural failure of these pipelines. Onshore buried pipelines can be subjected to axial, bending, shear, and other complex loadings due to geotechnical movements and temperature variations. In addition, these pipes experience internal pressure from the fluids that they transport. Pipeline industry is concerned about the structural behavior and integrity of corroded pipelines when subjected to various loads and load combinations. Hence, structural behavior and failure conditions of corroded pipelines under various loads and load combinations need to be understood for safe operation of these field pipelines. Literature review did not reveal any study that determined the structural behavior of corroded steel pipes when subjected to monotonically increasing axial compressive force with constant internal pressure. Therefore, an experimental study was completed to determine the structural behavior of X46 steel line pipe subjected to monotonically increasing axial compression and constant internal pressure as the geometry of corrosion and level of internal pressure change. This study shows that the axial load carrying capacity reduces as the corrosion depth increases. However, this pipe is highly ductile and does not pose any threat to the structural integrity of the pipe when subjected to monotonically increasing axial deformation and constant internal pressure.

Select this Article		A Co‐Rotational Model for the Cyclic Analysis of Light‐Frame Wood Shear Walls and Diaphragms Weichiang Pang, A. M. ASCE and Seyed Masood Hassanzadeh Shirazi, S. M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000595 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a new 2D shear wall and diaphragm model developed as part of a Network for Earthquake Engineering Simulation (NEES) project, entitled “NEES‐Soft: Seismic Risk Reduction for Soft‐Story Woodframe Buildings”. A large portion of the older multi‐story buildings in California region were constructed with a deficiency which makes them vulnerable to collapse in the firsts‐story during earthquakes. This deficiency is referred to as “soft‐story”. The new model presented in this paper is developed using a co‐rotational formulation which makes it suitable for modeling the side‐sway collapse of wood shear walls under large displacement as well as estimating the in‐plane stiffness of floor diaphragms. To achieve high computational efficiency, a nodal condensation technique is utilized to eliminate the degrees of freedom (DOFs) associated with the nail connections from the global DOFs of the model. In order to verify the validity of the new model, the model was coded into a computer program and was utilized to analyze selected shear walls and diaphragm tested by various institutions and research programs. Good agreements were observed between the test and model predicted backbone and cyclic curves for shear walls with various levels of gravity loads and different anchorage conditions. The model is highly flexible and has been shown to be able to model older shear wall construction with horizontal sheathing boards and diagonal bracings.

Select this Article		Experimental Studies on Deep Trapezoidal Sheeting with Perforated Webs Sándor Ádány, Mansour Kachichian, Balázs Kövesdi, and László Dunai Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000593 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract In this paper the behaviour of deep trapezoidal sheeting with perforated webs is studied. The analysed panel has longitudinal stiffeners both in the webs and flanges, which improves the load bearing capacity, but makes the behaviour more complicated. The considered panel is produced with and without web perforations. When web perforation is applied, it is located in the middle part of the web. The primary aim of web perforation is to enhance noise resistance, but it also has an influence on the static behaviour. Since reliable design rules for web perforated trapezoidal sheeting panels are not available, an experimental program is undertaken: panels with and without web perforations are tested in parallel. The test setup and specimens are designed to provide information on all the behaviour modes. On the basis of the test results, it is possible to define the degrading effect of web perforation on the rigidity, bending and shear resistances, and on the resistance to direct transverse forces close to and far from the panel end. The experimental results are compared to proposals found in the relevant literature. On the basis of the test results, reduction factors might be proposed to consider the effect of web perforation in the design of the investigated sheeting panel.

Select this Article		Modeling Force Transfer around Openings in Wood‐Frame Shear Walls Minghao Li, Frank Lam, Borjen Yeh, Tom Skaggs, Doug Rammer, and James Wacker Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000592 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presented a modeling study on force transfer around openings (FTAO) in wood‐frame shear walls detailed for FTAO. In order to understand the load transfer in the walls, this study used a finite element model WALL2D which is able to model individual wall components including framing members, sheathing panels, oriented panel‐frame nailed connections, framing connections, hold‐down connections, and strap connections for reinforcing the corners of openings. The various wall models were validated through laboratory testing of 12 full‐scale 2.44 × 3.66 m (8’ × 12’) shear wall configurations which included a variety of opening types and sizes. At the wall design load level, the predicted strap forces around openings also agreed well with the test results in contrast with four simplified analytical methods commonly used in designing shear walls with openings detailed for FTAO. This wall model thus presents a useful tool to check the accuracy of the simplified methods and develop a better understanding of the behavior of wood‐frame shear walls with openings.

Select this Article		Experimental Investigation of Non‐Ductile Reinforced Concrete Corner Beam‐Column Joints with Floor Slabs Sangjoon Park, Ph.D. and Khalid M. Mosalam, Ph.D., P.E., M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000591 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract The paper presents the experimental investigation of full‐scale reinforced concrete (RC) corner beam‐column joints without transverse reinforcement in the joint region leading to non‐ductile behavior in many exiting RC buildings. The experimental study considered two design parameters, namely joint aspect ratio and beam longitudinal reinforcement ratio. Four corner beam‐column joint specimens were constructed with transverse beams and floor slabs, and tested under quasi‐static cyclic loading. The specimens experienced joint shear failure without beam hinging mechanism due to the absence of transverse reinforcement in the joint region. Based on the test results, the paper discusses the effects of the above‐mentioned two design parameters and the floor slab on the behavior of corner beam‐column joints. The joint shear strengths obtained from the test specimens are compared to the strength recommendations of the ASCE/SEI 41‐06 provisions.

Select this Article		Influence of Slenderness on High Strength Rectangular Concrete‐Filled Tubular Columns with Axial Load and Non‐Constant Bending Moment D. Hernández‐Figueirido, M. L. Romero, J. L. Bonet, and J. M. Montalvá Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000590 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Forty‐nine experimental tests were conducted on rectangular and square tubular columns filled with high strength concrete (f'_c=90 MPa) subjected to axial load and a non‐constant bending moment distribution. The test parameters were the length (2, 3 and 4 m), the cross‐section aspect ratio (square or rectangular), the wall thickness (4 or 5 mm), and the ratio of the top and bottom first order eccentricities r=e_top/e_bottom (1, 0.5, 0 and −0.5). The effect of slenderness combined with the influence of variable curvature is compared with the design loads from AISC 360‐10 and Eurocode 4. The results show that, for the slender elements of this experimental campaign, both codes present a similar error close to 4%. The small error margin indicates that both standards are applicable to high strength concrete, although the concrete tested is outside the upper bond of Eurocode 4 and AISC's specifications. However there are particular cases which present excessive unsafe errors. These errors correspond to the cases where the second order effects are more important and are due to an overestimation of the flexural stiffness EI, what indicates that it needs correction.

Select this Article		Vulnerability and Risk Assessment of Single‐Layer Reticulated Domes Subjected to Earthquakes X. D. Zhi, G. B. Nie, F. Fan, and S. Z. Shen Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000589 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract In order to provide a good understanding of the damage states of single‐layer reticulated domes under earthquake loading, a number of Increment Dynamic Analyses (IDA) are carried out on domes with different spans, rise‐span ratios, roof weights and other parameters. A model is proposed for the quantitative evaluation of damage. The damage states for single‐layer reticulated domes are defined based on their structural dynamic performance and corresponding damage factors. The vulnerability of single‐layer reticulated domes is shown using fragility curves with different damage states. A model of probability distribution for seismic hazard, structural damage probability and various losses, including direct and indirect economic loss and maimed and fatality loss, is discussed for assessing risk. The risk assessment of a single‐layer reticulated dome is performed for different seismic intensities for its loss or fatality acceptability.

Select this Article		Validation of a Modified Steel Bar Model Incorporating Bond‐Slip for Seismic Assessment of Concrete Structures Michele D'amato, Franco Braga, Rosario Gigliotti, Sashi Kunnath, F. ASCE, and Michelangelo Laterza Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000588 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract In this paper the implementation and validation of a modified steel bar model including bond‐slip of longitudinal bars proposed in a companion paper is discussed. The model is developed on the key assumption of linear slip field along the steel bar with different configurations at the ends of the bar. It is demonstrated that the simplified model is capable of predicting the axial slip displacement with suitable accuracy compared to a refined model but with considerably fewer computational steps. The proposed model avoids nested iterations in the context of fiber model discretization of a section that requires the representation of all actions in terms of stress and strain. The model is applied to two component tests — one with poor and another with improved reinforcing detailing. Findings from the simulations indicate that the proposed model is more suitable for use in connections with poor detailing and pronounced slip in the plastic hinge zones.

Select this Article		A Modified Steel Bar Model Incorporating Bond‐Slip for Seismic Assessment of Concrete Structures Franco Braga, Rosario Gigliotti, Michelangelo Laterza, Michele D'Amato, and Sashi Kunnath, F. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000587 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a simplified model for describing the response of a longitudinal bar embedded in concrete taking into account the bond‐slip phenomenon. The model is developed by assuming a linear bond‐slip field along the bar anchorage length and provides a simplified stress‐strain relationship to assign to the longitudinal reinforcement. The analytical approach adopted makes the proposed model very convenient from a computational standpoint because, unlike many other refined models, it does not require a multi‐level iterative process. Moreover, the assumptions made are particularly appropriate for modeling bond‐slip of smooth bars generally used in older reinforced concrete buildings. The implementation strategy of the proposed bond‐slip model in a general‐purpose nonlinear structural analysis software and comparisons with experimental results are discussed in a companion paper.

Select this Article		Finite Element Model Updating for Assessment of Progressive Damage in a Three‐Story Infilled RC Frame Babak Moaveni, A. M. ASCE, Andreas Stavridis, A. M. ASCE, Geert Lombaert, Joel P. Conte, M. ASCE, and P. Benson Shing, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000586 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a study on the identification of progressive damage, using an equivalent linear finite element model updating strategy, in a masonry infilled reinforced concrete (RC) frame that was tested on a shake table. A 2/3‐scale, three‐story, two‐bay, infilled RC frame was tested on the UCSD‐NEES shake table to investigate the seismic performance of this type of construction. The shake table tests induced damage in the structure progressively through scaled historical earthquake records of increasing intensity. Between the earthquake tests and at various levels of damage, low‐amplitude white‐noise base excitations were applied to the infilled RC frame. In this study, the effective modal parameters of the damaged structure have been identified from the white‐noise test data with the assumption that it responded in a quasi‐linear manner. Modal identification has been performed using a deterministic‐stochastic subspace identification method based on the measured input‐output data. A sensitivity‐based finite element model updating strategy has been employed to detect, locate, and quantify damage (as a loss of effective local stiffness) based on the changes in the identified effective modal parameters. The results indicate that the method can reliably identify the location and severity of damage observed in the tests.

Select this Article		Residual Stress Tests of High Strength Steel Equal Angles Huiyong Ban, Gang Shi, Yongjiu Shi, and Yuanqing Wang Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000585 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract The residual stress is one of the most important imperfections for steel structure members due to its significant effects on the buckling behavior. In order to quantify the residual stresses in 420MPa high strength steel hot‐rolled equal angle sections, an experimental study was conducted by using the sectioning method. The residual stress magnitude and distribution for 15 sections were obtained, and the effects of width‐thickness ratios were clarified. Based on the test results, it was found that the ratio between the residual stress and the steel yield strength for 420MPa steel equal angles was much smaller than that of normal strength steel angles; however the distribution was analogous. The residual magnitudes significantly correlated with the width‐thickness ratios of legs. In addition, the calculation formulae for the residual stress magnitudes were proposed in which the width‐thickness ratios of angle legs were taken into account, and 3 distribution models were established to be incorporated in the buckling analysis. This fundamental research and conclusions presented may provide useful experimental data and calculation method for further studies on the residual stress and buckling behavior of high strength steel members.

Select this Article		Fatigue Assessment and Service Life Prediction of Existing Steel Bridges by Integrating SHM into a Probabilistic Bi‐linear S‐N Approach Mohamed Soliman, S. M. ASCE, Dan M. Frangopol, Dist. M. ASCE, and Kihyon Kown, S. M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000584 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Fatigue assessment of several steel bridge details, having equivalent stress range below the constant amplitude fatigue threshold (CAFT), showed that many of these details are free of cracks, although the remaining life calculations predicted that they should have already been suffering from cracks. This proves that the current methods for predicting the fatigue remaining life of steel bridges are conservative and may lead to unnecessary retrofit and rehabilitation actions. For a better fatigue life prediction, a bi‐linear S‐N approach has been proposed. In this approach, the bi‐linear S‐N lines have different slopes above and below CAFT. This paper addresses fatigue assessment and service life prediction of existing fatigue‐prone steel bridges by integrating structural health monitoring (SHM) data into a probabilistic bi‐linear S‐N approach. The effect of changing the value of the slope of the AASHTO S‐N lines below the CAFT on the fatigue life is investigated through a parametric study. In addition, an existing steel bridge is used to illustrate the proposed probabilistic approach.

Select this Article		Defect Tolerance for Cast Steel Connections in Braced Frames Tsutomu Iwashita, Jeffrey A. Packer, and Juan‐Carlos de Oliveira Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000583 Posted ahead of print 22 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract During the past decade, various steel casting products for steel building structures have been developed, such as connectors between brace members and gusset plates in braced frames. Some casting products are welded to steel sections such as tubular members and I‐section members in building structures, where these members are expected to develop their capacity during a large‐scale earthquake. In this situation, brittle fracture can be another concern of the casting products if there are defects in the connections. A study of defect tolerance for cast steel connections is hence very important in order to prevent brittle fracture from weld defects or casting defects. This paper describes defect tolerances for cast steel connections in braced frames and explores the possibility of brittle fracture from assumed defects in typical cast steel connectors. A parametric study, which investigates the sensitivity of brittle fracture to defect size, defect location and material mis‐match effects, is described through cast steel connector models. A toughness scaling model is used for evaluating the occurrence of brittle fracture from assumed defects in the models.

Select this Article		Analysis of Thin‐Walled Straight Beams with Generally‐Shaped Closed Sections Using Numerically‐Determined Sectional Deformation Functions Gang‐Won Jang, Myung‐Jin Kim, and Yoon Young Kim Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000582 Posted ahead of print 21 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This investigation presents one‐dimensional static and eigenvalue analyses of thin‐walled straight beams with generally‐shaped closed single‐ or multi‐cell sections. For accurate beam analysis, sectional warping and distortional deformations should be considered in addition to the standard Timoshenko displacement field, but it is difficult to obtain the deformation functions analytically for arbitrarily‐shaped sections. Thus, we propose a numerical method to obtain sectional deformations for any arbitrarily‐shaped sections. Once the deformations are identified, they can be integrated over a cross section to yield one‐dimensional higher‐order beam equations. For the numerical determination, the cross section of a thin‐walled beam is modeled as a beam frame where the warping and distortional deformation functions of the section are identified as the eigenmodes of the frame model; the lowest few energy mode sets of in‐planar and out‐of‐planar modes are selected as the distortional and warping deformation functions, respectively. The validity of this approach is checked by comparing the present results with shell finite element results. For numerical tests, several thin‐walled closed sections including those with flanges or varying wall thicknesses are considered. The effect of the number of selected warping and distortion sets on solution convergence is also investigated.

Select this Article		Three‐Dimensional Hydromechanical Sectional Analysis of Cracked Non‐Prismatic Concrete Spillway Piers Lucian Stefan and Pierre Léger, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000579 Posted ahead of print 10 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Several concrete hydraulic structures, such as spillway piers, must be considered as three‐dimensional (3D) components subjected to 3D loads. A very convenient approach to perform stability analysis of concrete dams is the so‐called “gravity method”, leading to the solution of a PMM problem (axial force P and biaxial bending moments M_x, M_y) assuming linear normal stress distribution. If cracking is taking place, water penetrates in cracks inducing the development of full uplift pressures. Sliding safety factors (SSF) are computed using shear force resultants V_x, V_y and a Mohr‐Coulomb failure criterion while ignoring torsion T (VVT). This paper presents a 3D extension of the gravity method for cracked planar concrete sections of arbitrary geometry subjected to arbitrary loads (PMM‐VVT). To compute the shear stress distribution, a VVT sectional analysis algorithm has been developed based on the Theory of Elasticity including Saint‐Venant and warping torsional components combined with triangular 2D finite elements (FE). Afterwards, the SSF on the failure plane is computed from the integration of normal stresses on the remaining uncracked area where the Mohr‐Coulomb criterion (considering the shear stresses from the VVT solution) has not been locally exceeded. Two validation examples and a case study of an actual pier are presented to illustrate the accuracy and efficiency of the proposed approach as compared to full 3D FE analyses.

Select this Article		Out‐of‐Plane Strength of Confined Masonry Walls Jorge Varela‐Rivera, Joel Moreno‐Herrera, Ivan Lopez‐Gutierrez, and Luis Fernandez‐Baqueiro Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000578 Posted ahead of print 10 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents the results of a study on the out‐of‐plane behavior of confined masonry walls. Six full‐scale walls were tested in the laboratory under incremental uniform pressures. Walls with different aspect ratios, slenderness ratios, and in‐plane stiffness of confining elements were considered. The spring‐strut method was developed in this work to determine the out‐of‐plane strength of the walls. Experimental out‐of‐plane strengths are compared with those obtained with analytical models based on this spring‐strut method, the yield line method, the failure line method, and the compressive strut method. Based on the experimental results, it was concluded that, for walls with similar geometry, the out‐plane strength depends mainly on the in‐plane stiffness of the confining elements. From the comparison between experimental and analytical results, it was concluded that the out‐of‐plane strengths are well predicted with the model based on the spring‐strut method, are underestimated with that based on the yield and failure line methods, and are overestimated with the model based on the compressive strut method.

Select this Article		Predicting the Usefulness of Monitoring for Identifying the Behavior of Structures James‐A. Goulet, A. M. ASCE and Ian F. C. Smith, F. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000577 Posted ahead of print 10 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Structures can be better understood when measurement data is used to improve modeling of structural behavior. Our capacity to interpret data depends on aspects such as the choice of model class, model parameters (and their range of possible values) and the extent of uncertainties influencing models and measurements. The objective of this paper is to determine probabilistically to what degree measurements are useful for structural identification with respect to the aspects mentioned above. A metric, expected identifiability, is proposed to be used prior to monitoring. The new methodology is based on three performance indices: the expected number of candidate models, the expected prediction ranges and a combination of the two. Since it does not require intervention on the structure, the method can be used as a tool to support prioritization of decisions related to full‐scale testing. These features are illustrated through the study of the Langensand Bridge (Switzerland). In this example, the methodology shows that increases in modeling uncertainties significantly hinders the usefulness of measurements for identifying model parameter values. The predictive capability of the method proposed is verified by the agreement with observations made during a recent structural identification exercise. Quantifying the expected identifiability provides a tool to support infrastructure decision‐making such as determining to what extent certain structural monitoring plans are useful.

Select this Article		Seismic Design and Analysis of Steel Plate Shear Walls with Coupling Daniel J. Borello, E.I.T., S. M. ASCE and Larry A. Fahnestock, P.E., M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000576 Posted ahead of print 1 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Special Steel Plate Shear Walls (SPSW) are an economical seismic lateral force resisting system used throughout North America and Japan. Architectural constraints often encourage the designer to place a pair of planar SPSWs adjacently. A logical extension of the planar SPSW system is to link two SPSWs together with coupling beams to form a Steel Plate Shear Wall with Coupling (SPSW‐WC). SPSW‐WCs have only been addressed in a limited fashion by prior research and current code provisions contain no guidance for their design. This research studied the force transfer mechanisms, behavior and design of SPSW‐WCs. A design methodology was developed by extending the capacity design procedures that are currently used for planar SPSWs. Fourteen prototype buildings were designed using this methodology and representative numerical models were developed. These numerical models were validated and then used to conduct static pushover analysis and earthquake response history analysis. The results of the numerical simulations demonstrate that SPSW‐WC systems exhibit robust seismic performance that is equivalent to or better than similar planar SPSW systems and the SPSW‐WC systems improve architectural flexibility and material efficiency.

Select this Article		Design Strength of Locally Buckling Stub Lipped Channel Columns M. V. Anil Kumar and V. Kalyanaraman Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000575 Posted ahead of print 1 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract The compressive strength of the cold‐formed steel (CFS) lipped channel (LC) members may be governed by yielding, the local, distortional or overall buckling and any possible interaction among these modes. The Direct Strength Method (DSM) has been advanced recently for evaluating the strength of CFS LC beams and columns. While the DSM is an improvement over the other methods in terms of simplicity and accuracy, further improvement by minor modification to the DSM is possible if all the parameters that affect the strength of such members is properly understood and accounted for. In this study we are discussing the DSM equations for evaluating the strength of members that fail after experiencing only local buckling. The strength of such members, according to DSM, is a function of only the ratio of yield strength of the section, P_y, to the elastic local buckling load (P_crℓ) (also equal to the reciprocal of square of the non‐dimensional local buckling slenderness ratio, 1/λ_ℓ²). This study indicates that the relative area of the stocky elements of the cross section, which are less vulnerable to elastic local buckling, also influences the strength of such members. Using the experimental results available in the literature and the finite element analysis data generated in this study, the behaviour and strength of stub LC compression members experiencing only local buckling before failure by yielding, is evaluated. Simple modifications are suggested to the currently available DSM equations to more accurately evaluate the strength of such members.

Select this Article		Development of a New Composite Slab System Using a Carbon‐Fiber‐Blended Cementitious Adhesive Isamu Yoshitake, Atsushi Ogawa, Yail J. Kim, and Yoichi Mimura Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000574 Posted ahead of print 1 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents an experimental study to develop a new composite slab system consisting of concrete deck with reinforcing bars, steel plates welded with rib connectors, and a carbon‐fiber‐blended cementitious adhesive. The adhesive includes unique characteristics such as rust‐resistance and water‐proof and can be sprayed to a steel substrate. The foci of the present research are bond performance of the adhesive that is an interfacial medium between the concrete and steel plates, bond‐slip response of the interface, and structure‐level investigations. Test parameters include the presence of adhesive layer, age of concrete‐steel interface linked with the adhesive, and configuration of rib connectors. Adequate curing time of the concrete‐steel interface with the adhesive is found to be at least seven days to achieve reasonable composite action. The adhesive layer significantly improves the performance of the interface, including bond‐slip and load‐carrying capacities. The shape of perforation in the rib is not a significant factor on the behavior of the interface. Although the proposed composite concept is promising, progressive bond deterioration is an important consideration and further research is necessary.

Select this Article		Mechanism of Collapse of Tall Steel Moment Frame Buildings under Earthquake Excitation Swaminathan Krishnan and Matthew Muto Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000573 Posted ahead of print 1 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract The mechanism of collapse of tall steel moment frame buildings is explored through three‐dimensional nonlinear analyses of two 18‐story steel moment frame buildings under earthquake excitation. Both fracture‐susceptible as well as perfect‐connection conditions are investigated. Classical energy balance analysis shows that only long‐period excitation imparts energy to tall buildings large enough to cause collapse. Under such long‐period motion, the shear beam analogy alludes to the existence of a characteristic mechanism of collapse or a few preferred mechanisms of collapse for these buildings. Numerical evidence from parametric analyses of the buildings under a suite of idealized sawtooth‐like ground motion time histories, with varying period (T), amplitude (peak ground velocity, PGV), and duration (number of cycles, N), is presented to support this hypothesis. Damage localizes to form a “quasi‐shear” band over a few stories. When the band is destabilized, sidesway collapse is initiated and gravity takes over. Only one to five collapse mechanisms occur out of a possible 153 mechanisms in either principal direction of the buildings considered. Where two or more preferred mechanisms do exist, they have significant story‐overlap, typically separated by just one story. It is shown that a simple work‐energy relation applied to all possible quasi‐shear bands, combined with plastic analysis principles can systematically identify all the preferred collapse mechanisms.

Select this Article		Force‐ and Displacement‐Based Seismic Performance Parameters for Reinforced Masonry Structural Walls with Boundary Elements Bennett R. Banting, S. M. ASCE and Wael W. El‐Dakhakhni, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000572 Posted ahead of print 1 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract There is a need to evaluate existing and introduce new masonry construction techniques within a performance‐based seismic design context to advance their adoption in the next generation of seismic design codes in North America. In this regard, a reinforced masonry (RM) structural wall system that incorporates confining boundary elements in the plastic hinge region presently lacks specific design requirements in the MSJC and CSA S304.1 design codes. In addition, RM structural wall systems are omitted completely from the plan to develop a new performance‐based seismic design methodology laid out by FEMA 445. This paper presents experimental results of four specially‐detailed RM structural walls subjected to fully‐reversed cycles of displacement‐controlled loading as tested by the authors. In addition, the resulting analysis also includes one wall from a previous study for comparison purposes. All walls were detailed with lateral reinforcing ties confining a grouted core and four vertical reinforcement bars located at each of the wall ends. The design and detailing of the walls represented a range of parameters that would be anticipated to vary within low‐ to medium‐rise RM buildings. Each of the half‐scale walls had overall dimensions of 1.8 m × 4.0 m but varied by: the level of applied axial load, the presence of inter‐storey floor slabs and the presence of confining boundary elements above the 1^st storey height. The results of this experimental program indicate that boundary elements delayed the onset of buckling in the vertical reinforcement and reduced the impact of faceshell spalling on overall wall strength degradation. At 20% degradation from ultimate strength, top drifts ranged from 1.82% to 3.73% and displacement ductilities ranged from 6.6 to 15.2. This study is the first of a series of studies in McMaster University currently focused on introducing a broad set of experimental evidence aiming at establishing a new category of RM seismic force resisting systems in North American building codes.

Select this Article		Benchmark Footbridge for Vibration Serviceability Assessment under Vertical Component of Pedestrian Load Stana Živanović Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000571 Posted ahead of print 1 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Vibration serviceability criteria are governing the design and determining the cost of modern, slender footbridges. Efficient and reliable evaluation of dynamic performance of these structures usually requires a detailed insight into the structural behaviour under human induced dynamic loading. Design procedures are becoming ever more sophisticated and versatile and for their successful use a thorough verification on a range of structures is required. The verification is currently hampered by a lack of experimental data that are presented in the form directly usable in the verification process. This study presents a comprehensive experimental data set acquired on a box girder footbridge that is lively in the vertical direction. The data are acquired under normal operating conditions, and are presented using a range of descriptors suitable for easy extraction of desired information. This will allow researchers and designers to use this bridge as a benchmark structure for vibration serviceability checks under vertical component of the pedestrian loading. In addition, capabilities of a sophisticated force model (developed for walking over rigid surfaces) to predict vibrations on this lively bridge are investigated. It was found that there are discrepancies between computed and measured responses. It was argued that these differences are a consequence of the pedestrian‐structure interaction on this lively bridge. The interaction was then quantified in the form of pedestrian contribution to the overall damping of the human‐structure system.

Select this Article		In‐Plane Elastic Buckling of Shallow Parabolic Arches under an External Load and Temperature Changes Jianguo Cai, Yixiang Xu, Ph.D., Jian Feng, Ph.D., and Jin Zhang, Ph.D. Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000570 Posted ahead of print 1 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper studies the in‐plane stability of rotationally restrained shallow arches subjected to a vertical uniform load and temperature changes below 100°C. The virtual work principle method is used to establish the non‐linear equilibrium and buckling equations. Analytical solutions for the non‐linear in‐plane symmetric snap‐through and asymmetric bifurcation critical loads are obtained. Then the effects of the uniform temperature field and temperature gradients on the in‐plane stability for arches are studied. It has been found that the influence of temperature variations on the critical loads for both the symmetric snap‐through and asymmetric bifurcation modes is significant. The critical loads increase with an increase of the uniform temperature field and a decrease of temperature gradients. Furthermore, the effect of temperature changes on the critical load increases with the span‐rise ratio m of arches. It can also be found that increasing the stiffness of rotational springs will increase the effect of the uniform temperature field but reduce the effect of the temperature gradients.

Select this Article		Ambient and Forced Vibration Testing of a Reinforced Concrete Building before and after Its Seismic Retrofitting Serdar Soyoz, Ertugrul Taciroglu, Kutay Orakcal, Robert Nigbor, Derek Skolnik, Hilmi Lus, and Erdal Safak Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000568 Posted ahead of print 14 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract We investigated the effects of seismic retrofitting on the modal characteristics of a six‐story reinforced concrete building located in Istanbul, Turkey. We carried out ambient vibration surveys before, during, and after the retrofitting work, which took place between June and December 2010. The building was retrofitted via jacketing of columns, addition of structural walls, and construction of a mat foundation. These studies were complemented with data from forced vibration tests that we performed with an eccentric mass shaker after the retrofitting work was completed. During retrofitting, partitions were demolished; and as a result, the first modal frequency of the building decreased by 11%, based on the results of the ambient vibration survey. The ambient vibration survey also showed that the modal frequencies after the seismic retrofitting increased by almost 96%. During the forced vibration tests, the building was excited around its modal frequencies using an eccentric mass shaker. It was found that the modal damping values increased with the amplitude of the excitation force.

Select this Article		Real‐Time Condition Assessment of RAPTOR Telescope Systems Christopher J. Stull, Stuart G. Taylor, James Wren, David L. Mascareñas, and Charles R. Farrar Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000567 Posted ahead of print 2 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract The RAPid Telescopes for Optical Response (RAPTOR) observatory network consists of several ground‐based, autonomous, robotic, astronomical observatories primarily designed to search for astrophysical transients called gamma‐ray bursts. In order to make these observations, however, the RAPTOR telescopes must remain in peak operating condition at a high duty‐cycle. Currently, the telescopes are maintained in an ad hoc manner, often in a run‐to‐failure mode. The required maintenance logistics are further complicated by the fact that many of the observatories are situated in remote locations. In order to ameliorate this situation, an effort has been initiated to develop a structural health monitoring (SHM) system capable of real‐time, remote assessment of the RAPTOR telescopes. This paper summarizes the results from that effort. Common damage scenarios are identified to guide the instrumentation of the telescope system. A comprehensive analysis of the data acquired during experimental testing is then presented, highlighting the capability of the SHM system to discern between damaged and undamaged states. The paper concludes with a summary of future planned refinements for the RAPTOR SHM system.

Select this Article		Cyclic Out‐Of‐Plane Behaviour of Slender Clay Brick Masonry Walls Seismically Strengthened Using Posttensioning Najif Ismail, S. M. ASCE and Jason M. Ingham, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000565 Posted ahead of print 2 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract Equations for the design of a posttensioned seismic retrofit of unreinforced clay brick masonry walls are discussed and results from an associated experimental program are reported. A total of eight (08) full scale multi‐wythe vintage solid clay brick masonry walls were subjected to uniformly distributed one directional and reverse cyclic out‐of‐plane loading, of which two (02) walls were tested as‐built and six (06) walls were seismically retrofitted using unbonded posttensioning. Test wall configurations and constituent masonry materials were selected to replicate typical characteristics of historic clay brick masonry walls. The test walls were seismically retrofitted by applying varying magnitudes of posttensioning using a single tendon, inserted into a cavity located at the centre of each test wall. Several aspects pertaining to the seismic behaviour of posttensioned masonry walls were investigated, including damage patterns, force‐displacement behaviour, tendon stress variation, wall secant stiffness, hysteretic energy dissipation, toughness modulus, and damping ratio. Finally, measured performance parameters of the test walls were compared to the corresponding values predicted using the proposed design equations.

Select this Article		Analysis of the Lateral Thrust in Bolted Steel Buckling‐Restrained Braces. Part 2: Engineering Analytical Estimates Francesco Genna and Piero Gelfi Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000564 Posted ahead of print 2 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract Part 1 of this work was concerned with the experimental and numerical analysis of the lateral force, or thrust, exerted by the inner core of a buckling‐restrained brace (BRB) when, after buckling in compression, it arrives into contact with the external retaining case. Here, always considering the case of a steel bolted BRB, with an empty gap between core and containment struts, we attempt the derivation of engineering analytical expressions for such a thrust. It is found that the relationship between applied axial force and buckled wavelength does not obey Euler's formula.

Select this Article		New Design Rules for the Shear Strength of LiteSteel Beams with Web Openings Poologanathan Keerthan and Mahen Mahendran Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000563 Posted ahead of print 2 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract LiteSteel beam (LSB) is a new cold‐formed steel hollow flange channel section produced using a patented manufacturing process involving simultaneous cold‐forming and dual electric resistance welding. The LSBs are commonly used as floor joists and bearers with web openings in residential, industrial and commercial buildings. Their shear strengths are considerably reduced when web openings are included for the purpose of locating building services. However, no research has been undertaken on the shear behaviour and strength of LSBs with web openings. Therefore experimental and numerical studies were undertaken to investigate the shear behaviour and strength of LSBs with web openings. In this research, finite element models of LSBs with web openings in shear were developed to simulate the shear behaviour and strength of LSBs including their buckling characteristics. They were then validated by comparing their results with available experimental test results and used in a detailed parametric study. The results showed that the current design rules in cold‐formed steel structures design codes are very conservative for the shear design of LSBs with web openings. Improved design equations have been proposed for the shear capacity of LSBs with web openings based on both experimental and parametric study results. An alternative shear design method based on an equivalent reduced web thickness was also proposed. It was found that the same shear strength design rules developed for LSBs without web openings can be used for LSBs with web openings provided the equivalent reduced web thickness equation developed in this paper is used. This is a significant advancement as it simplifies the shear design methods of LSBs with web openings considerably.

Select this Article		Vierendeel Bending Study of Perforated Steel Beams with Various Novel Web Opening Shapes, through Non‐Linear Finite Element Analyses Konstantinos Daniel Tsavdaridis and Cedric D'Mello Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000562 Posted ahead of print 2 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract The Vierendeel mechanism is always critical in perforated steel beams with single large web openings, where global shear forces and Vierendeel moments co‐exist. Thus far, the main parameters that are known to affect the structural behavior of such beams are the depth of the web opening, the critical opening length of the top tee‐section and the web opening area. A comprehensive Finite Element (FE) study of four sizes of perforated steel sections with three different sizes of eleven standard and novel non‐standard web opening shapes was undertaken, and their primary structural characteristics presented in detail in order to provide a simple design method for general practice. The different geometric parameters were isolated and studied in order to understand the significance of their effects and in turn advance the knowledge on the performance of perforated steel beams. An elaborate FE model was established, with both material and geometrical non‐linearity, allowing load redistribution across the web openings and formation of the Vierendeel mechanism. The reduction of the global shear capacities, due to incorporation of the local Vierendeel moments acting on the top and bottom tee‐sections, was obtained directly from the FE analysis. Following that, a comparison of the global shear‐moment (V/M) interaction curves of the steel sections with various web opening shapes and sizes was established and empirical generalized V/M interaction curves developed. Moreover, the accurate position of the plastic hinges was determined together with the critical opening length and the Vierendeel parameter. This work has now shown that the shape of the web opening can also significantly affect the structural behavior of perforated beams, as opposed to the equivalent rectangular shape predominately used so far. In addition, the effect of the position of the web opening along the length of the perforated beam was revealed. The importance of the parameters that affect the structural performance of such beams is illustrated. The thorough examination of the computational results has led to useful conclusions and an elliptical form of a web opening is proposed for further study. The outcome of this study is considered as being relevant for practical applications.

Select this Article		Shear Strength of Cold‐Formed Steel Sheet in Bolted Connections Using Oversized Holes Cheng Yu, Ph.D., M. ASCE and Ke Xu Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000561 Posted ahead of print 2 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract The North American Specifications for the Design of Cold‐Formed Steel (CFS) Structural Members provides equations for determining the sheet shear strength in bolted connections when standard holes are used. In applications of oversized holes, the Specification requires experimental analysis to be conducted to ensure satisfactory performance. A research project was recently completed at the University of North Texas to investigate the behavior and performance of CFS bolted connections using oversized holes. This paper presents the findings on the sheet shear strength for oversized hole applications. The studied parameters in this research included the sheet thickness: from 0.762 mm to 2.997 mm; the connection type: single shear and double shear with single bolt; the bolt diameter: 6.4 mm, 9.5 mm, 12.7 mm, 15.9 mm. The experimental results indicate that the use of oversized holes without a washer did not significantly weaken the sheet shear strength. Recommendations are provided for predicting the nominal sheet shear strength.

Select this Article		SmartSync: An Integrated Real‐Time Structural Health Monitoring and Structural Identification System for Tall Buildings Tracy Kijewski‐Correa, Associate Professor, A. M. ASCE, Dae Kun Kwon, Research Assistant Professor, M. ASCE, Ahsan Kareem, Professor, Distinguished M. ASCE, Audrey Bentz, Graduate Student, S. M. ASCE, Yanlin Guo, Graduate Student, Sarah Bobby, Graduate Student, S. M. ASCE, and Ahmad Abdelrazaq, Executive Vice President, A. M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000560 Posted ahead of print 2 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract This study introduces a unique prototype system for Structural Health Monitoring, SmartSync, which utilizes the building's existing Internet backbone as a system of “virtual” instrumentation cables to permit modular and largely “plug‐and‐play” deployments. Within this framework, data streams from distributed heterogeneous sensors are pushed through network interfaces in real‐time and seamlessly synchronized and aggregated by a centralized server, which performs basic data acquisition, event triggering and database management, while also providing a interface for data visualization and analysis that can be securely accessed. The system enables a scalable approach to monitoring tall and complex structures that can readily interface variety of sensors and data formats (analog and digital) and can even accommodate variable sampling rates. This study overviews the SmartSync system, its installation/operation in the world's tallest building, Burj Khalifa, and proof‐of‐concept in triggering under dual excitations (wind and earthquake).

Select this Article		Modified Natural Excitation Technique for Stochastic Modal Identification Minwoo Chang and Shamim N. Pakzad Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000559 Posted ahead of print 2 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents an improvement to the Eigensystem Realization Algorithm (ERA) with Natural Excitation Technique (NExT) which is called the ERA‐NExT‐AVG method. The method utilizes a coded average of row vectors in each Markov parameter for evaluating modal properties of a structure. The modification is important since for the existing stochastic system identification methods the state‐space model, obtained from output sensor data, is usually over‐parameterized resulting is large systems. Solving such a problem can be computationally very intensive especially in the applications when using the computational capabilities of embedded sensor networks. As a way to improve the efficiency of the ERA‐NExT method, the proposed method focuses on the number of components in a single Markov parameter which can theoretically be minimized down to the number of structural modes. Applying the coded average column vectors as Markov parameters to the ERA, the computational cost of the algorithm is significantly reduced while the accuracy of the estimates is maintained or improved. Numerical simulations are performed for a shear frame model subjected to Gaussian white noise ground excitation. The efficiency of the proposed method is evaluated by comparing the accuracy and computational cost of the estimated modal parameters using the proposed method, with several other stochastic modal identification methods including the ERA‐Observer Kalman Filter Identification (OKID), ERA‐NExT, and Auto‐Regressive models (AR). The performance of the method is then evaluated by applying it to ambient vibration data from Golden Gate Bridge (GGB), collected using a dense wireless sensor network, and its vertical and torsional modes are successfully and accurately identified.

Select this Article		Analysis of the Lateral Thrust in Bolted Steel Buckling‐Restrained Braces Francesco Genna and Piero Gelfi Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000558 Posted ahead of print 21 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract This work presents an experimental and numerical analysis of the lateral forces exerted by the inner core of a buckling‐restrained brace (BRB) when, after buckling in compression, it arrives into contact with the external restraining case, from which it is separated by a small empty gap. Experiments are carried out on reduced scale specimens to measure the thrust acting on the containment struts. Refined, nonlinear 2D Finite Element (FEM) models are adopted to obtain numerical estimates of the thrust. The results show (i) the capability of 2D, plane stress FEM models to correctly reproduce the cyclic behavior of the studied BRBs, and (ii) the difficulty in accurately measuring/computing the thrust associated to a given axial load/displacement.

Select this Article		Prediction and Mitigation of Building Floor Vibrations Using a Blocking Floor Masoud Sanayei, Ningyu Zhao, Pradeep Maurya, James A. Moore, Jeffrey A. Zapfe, and Eric M. Hines Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000557 Posted ahead of print 21 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Buildings that are located near transportation corridors often experience floor vibrations induced by passing trains or traffic, which causes building owners some concern. In this paper, a mathematical, impedance‐based (wave propagation) model is presented for predicting traininduced floor vibrations in buildings. The model analytically predicts velocities, velocity ratios and impedances. Analytical predictions of the model were compared and validated with the measured floor vibrations in a 4‐story scale model building constructed by the authors. These predictions closely mimicked the measured responses. Using results from the method presented indicate that vibrations on upper floors can be mitigated by increasing the thickness of a floor at a lower level in the building. This lower level floor with the increased thickness is called a “blocking floor”. The scale model building was tested with and without a “blocking floor”. Predicted and measured responses of the scale model building using floor slabs with different thicknesses on the first floor are compared. It is concluded that the use of “blocking floor” can mitigate the transmission of structure‐borne vibration to the upper floors.

Select this Article		Effects of Elevated Temperatures on Double Shear Bolted Connections of Thin Sheet Steels Shu Yan and Ben Young, M.ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000556 Posted ahead of print 21 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract The current design rules of double shear bolted connections in the North American and Australian/New Zealand specifications for cold‐formed steel structures are mainly based on the design rules of single shear bolted connections. The design rules may not be applicable for elevated temperature conditions because the design rules of single shear bolted connections were based on tests conducted at ambient temperature. A total of 153 double shear bolted connection specimens was tested, where 102 specimens were tested using steady state test method and 51 specimens were conducted using transient state test method. Three thicknesses of thin sheet steel were used in the investigation. The connection strengths obtained from the tests were compared with the nominal strengths calculated from the North American, Australian/New Zealand and European specifications for cold‐formed steel structures. The current modification factor in the bearing strengths calculation for double shear bolted connections was evaluated at ambient temperature. The reduced tensile strengths of the thin sheet steels obtained from tensile coupon tests at elevated temperatures were used to calculate the nominal strengths of the connections. It is shown that the strengths of the double shear bolted connections predicted by the three specifications are generally conservative at elevated temperatures. Five failure modes were observed in the tests, namely bearing, tear out, net section tension, bolt shear and material failure.

Select this Article		Rotation‐Based Shear Failure Model for Lightly Confined Reinforced Concrete Columns Wassim M. Ghannoum and Jack P. Moehle Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000555 Posted ahead of print 21 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract A shear failure model for nonductile reinforced concrete columns that sustain flexural yielding prior to shear failure is proposed. The model, which relates shear failure to column end rotation, was derived by performing a forward stepwise linear regression on a database compiled from column tests. Critical parameters that affect rotation capacity at shear failure were found to be axial load, spacing (rather than amount) of transverse reinforcements, and nominal shear stress. The model is suitable for use in nonlinear frame analyses using either a lumped‐plasticity or fiber‐section column idealization. The model also can be used to determine rotation limits for performance‐based assessment of existing buildings.

Select this Article		Fatigue Performance of Stiffened Pole‐to‐Base Plate Socket Connections in High‐mast Structures Sougata Roy, Yeun Chul Park, Richard Sause, and John W. Fisher Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000554 Posted ahead of print 21 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Fatigue performance of stiffened pole‐to‐base plate socket connection in high‐mast lighting structures was evaluated by experimental and analytical studies. In absence of sufficient experimental data, constant amplitude fatigue limit (CAFL) of longitudinal stiffener terminations on pole walls is classified as Category E' in the existing American Association of State Highway and Transpiration Officials (AASHTO) specification. Fatigue performance of this connection in the thin walled tubular structures is controlled by localized secondary bending stress, the magnitude of which depends on the relative stiffness of the connecting elements. Ten full size high‐mast specimens having stiffened socket connection were tested under constant amplitude reversal loading to determine the fatigue resistance of this connection in finite and infinite life regimes. The specimen design was optimized by parametric Finite Element Analyses (FEA) and local stress approaches. FEA results were verified by conducting static test on an elaborately instrumented specimen. The test results demonstrated that an optimized stiffened connection can provide a CAFL of AASHTO Category D in commonly used high‐mast structures.

Select this Article		Reversed Cyclic Flexural Behavior of Spiral DSAW and Single Seam ERW Steel Pipe Piles Steven J. Fulmer, M.C.E., E.I., Mervyn J. Kowalsky, Ph.D., P.E., James M. Nau, Ph.D., P.E., M.ASCE, and Tasnim Hassan, Ph.D., AM.ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000553 Posted ahead of print 21 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents the findings of an investigation on the flexural performance of hollow steel pipe piles subjected to reversed cyclic loading. The testing evaluated both spirally double submerged arc welded (DSAW) and traditional longitudinal single seam electric resistance welded (ERW) pipe piles in order to determine the effects of the spiral welding manufacturing process on the structural performance of the pile. Some of the tests were conducted on previously driven piles in order to study the effects of driving stresses. The experimental results and observations indicated that the undesirable failure mode of spiral weld cracking did not control the ultimate limit state in any of the spirally welded specimens considered. Although weld fracture did occur in each spirally welded specimen, it did not develop until the specimen was subjected to large inelastic deformations and was ultimately the result of locally increased strains due to local buckling. Each traditional single seam specimen failed in a similar manner with pile wall local buckling developing at inelastic deformation levels comparable to that of the spirally welded specimens.

Select this Article		An Improved Finite Segment Method for Analyzing Shear Lag Effect in Thin‐Walled Box Girders Yuan‐Hai Zhang Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000552 Posted ahead of print 21 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Shear lag effect in thin‐walled box girders has been studied over several decades. However, the methods adopted in many papers have some deficiencies. In the present work, an improved displacement function for shear lag warping in a box girder with cantilever slabs is established. Based on the concept of generalized force corresponding to the generalized displacement for shear lag and the relevant geometrical properties, an improved finite segment method is proposed to simplify the shear lag analysis of complex box girders. The homogeneous solution of the governing differential equation for shear lag is adopted as the element displacement function. The formulas of the element stiffness matrix and the equivalent nodal force vector are derived. A general formula expressed in terms of the generalized moment is presented to calculate the stress. A finite element computer program is developed by using FORTRAN language and employed to analyze a cantilever box girder model and a continuous prestressed concrete box girder. The theoretical results are in good agreement with the test results, validating the proposed method and formulas. It is also the first time to reveal the characteristics of the generalized moment for shear lag in this paper.

Select this Article		Flexural Demand on Pin‐Connected Buckling‐Restrained Braces and Design Recommendations Junxian Zhao, Bin Wu, and Jinping Ou Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000549 Posted ahead of print 19 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract In the authors' previous study, the cyclic behavior of a novel type of pin‐connected angle steel buckling‐restrained braces (ABRB) was examined, and the failure mechanism in the core projection of ABRB, induced by excessive bending effect caused by end rotation, was discussed. In this paper, the occurrence mechanism of end rotation modes and bending effect in the core projection of ABRB are first investigated based on the previous test results. It shows that end rotation demands would be significantly increased with the presence of gap, and additional bending effect could be observed if end rotation demands were large enough to cause two‐point contact at the core ends. Then, a new method to predict the flexural demand on pin‐connected BRBs is proposed by considering the effect of end rotation modes, clearance, initial eccentricity and initial deflection of casing. The design criteria to prevent yielding of core projection is presented and further verified by the previous test results. Furthermore, the effects of key influential parameters on the flexural demand on core projection are discussed based on the analytical results. It is found that such bending effect can be significantly reduced by decreasing the gap or increasing the constrained length of core stiffening segment. The C‐mode end rotation with single curvature bending configuration is found to be generally the most unfavorable case for core projection design. Finally, several design recommendations are provided for pin‐connected BRBs.

Select this Article		Modeling of Fracture in the Sill‐Plate in Partially Anchored Shear Walls Erik Serrano, Johan Vessby, and Anders Olsson Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000548 Posted ahead of print 10 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract The current study relates to the topic of anchorage of shear walls. At times eccentric forces between the sheathing and the anchoring devices may be introduced in the sill‐plate. In severe cases such forces may cause the sill‐plate to split and to fail in a brittle manner. In this study, fracture mechanics was applied to develop a simple closed‐form hand calculation expression for estimation of the ultimate load capacity of the sill‐plate. Finite element analyses (FEA) using both linear elastic fracture mechanics (LEFM) theory and a nonlinear fictitious crack model (FCM) were also used to predict the ultimate load bearing capacity of the sill‐plate. The hand calculation model was compared with the FE‐models and a good agreement was obtained. The results obtained with the various fracture mechanics models were compared with results available from previously performed experimental tests and again good agreement was obtained. A general conclusion is thus that the fracture mechanics theory is an adequate approach for the case studied, and that the hand calculation expression developed could be useful for structural design.

Select this Article		Guidance for the Design of Spliced Columns Ana M. Girão Coelho, Ph.D., Pedro D. Simão, Ph.D., and Frans S. K. Bijlaard Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000546 Posted ahead of print 2 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Steel columns in sway and non‐sway frames that are spliced along their length generally have a lower strength capacity in compression. This load capacity can be further reduced due to the inevitable presence of small geometrical imperfections in the form of out‐of‐straightness of the column and column segments misalignment. The current work examines the buckling behavior of a framed spliced column with initial imperfections and the possibility of a non‐uniform cross‐section. A geometrically nonlinear model accounting for imperfect elastic buckling behavior is formulated using the differential equations of equilibrium. This is followed by a study of the imperfection sensitivity to the linearly evaluated critical load. A discussion on the variation of the load carrying capacity with the level of imperfections on a practical spliced column is also presented. The findings suggest that a spliced column can be considered equivalent to a prismatic Euler column, with an appropriate effective length, for design purposes. In this context, some implications for design are deduced from the presented analysis.

Select this Article		Nonlinear Seismic Analysis of Circular Concrete‐Filled Steel Tube Members and Frames Mark D. Denavit, S. M. ASCE and Jerome F. Hajjar, F. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000544 Posted ahead of print 2 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Accurate nonlinear formulations are necessary for the assessment of structures under seismic and other extreme loading. In this work, a three‐dimensional distributed plasticity beam element formulation for circular concrete‐filled steel tubes has been developed for nonlinear static and dynamic analyses of composite seismic force resisting systems. A mixed basis for the element formulation was adopted to allow for accurate modeling of both material and geometric nonlinearities. The formulation utilizes uniaxial cyclic constitutive models for the concrete core and steel tube that account for the salient features of each material, as well as the interaction between the two, including concrete confinement and local buckling of the steel tube. The accuracy of the formulation was verified against a wide variety of experimental results. The verification confirms the capability of the formulation to accurately produce realistic simulations of element and frame behavior.

Select this Article		Closed‐Form Prediction of the Alongwind‐Induced Fatigue of Structures Maria Pia Repetto and Giovanni Solari Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000543 Posted ahead of print 24 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract Wind‐induced fatigue is a crucial topic in the design of wind‐sensitive structures. In spite of this, methods proposed in literature are mainly addressed to research, or they are too much simplified for engineering applications. Thus, suitable engineering and standards procedures are almost totally lacking, this being a major shortcoming in structural and wind engineering. Starting from a closed form solution recently proposed by authors, this paper develops a novel engineering approach to evaluate the alongwind‐induced fatigue of structures and structural elements. This approach is based on a hierarchy of hypotheses that lead to a progressive simplification of the basic formulation. Two classes of formulae, referred to as the I and II level closed form solutions (CFS) are obtained and critically discussed with special concern for input parameters. The I level CFS implies three further simplifications joined together by the common aim of providing refined approximations of the reference target solution. The II level CFS implies three different simplifications joined together by the common aim of providing easy solutions on the safe side. This set of CFS are framed within a general procedure that any country or any society or any engineer can easily personalize to its own situation and requirement, this ranging from numerical tools up to manual engineering calculations and code provisions.

Select this Article		Lateral‐Torsional Buckling of Structural Concrete Beams: Experimental and Analytical Study Jonathan B. Hurff, A. M. ASCE and Lawrence F. Kahn, P.E., F. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000542 Posted ahead of print 24 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract Precast structural concrete beams have become longer and more slender, increasing the likelihood of a stability failure. Although there are methods to determine the lateral‐torsional buckling load for reinforced and prestressed concrete beams, there has been no conformity as to which is the more accurate method, nor do they account for initial imperfections. Six slender, rectangular pretensioned concrete beams were tested and showed that the lateral‐torsional stability behavior was similar to that of reinforced concrete beams except for (1) changes in material properties due to a different stress state and (2) the effects of prestressing on the cracking behavior of the cross‐section. The stability behavior proved to be sensitive to initial imperfections; therefore, both a geometric nonlinear stability analysis and a simplified equation were developed. The predictive methods were compared to the current and past results, and the analytical methods showed good correlation with all structural concrete experimental results. The results indicate that prestressed concrete beams are susceptible to lateral‐torsional buckling and initial imperfections serve to reduce the buckling load due to nonlinear geometric behavior and a non‐rectangular compression zone.

Select this Article		Experimental Investigations of Loading Rate Effects in Reinforced Concrete Columns W. Ghannoum, V. Saouma, G. Haussmann, K. Polkinghorne, M. Eck, and D. H. Kang Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000540 Posted ahead of print 24 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract Seismic loading rates can significantly affect the behavior of reinforced concrete (RC) elements, yet little data are available to quantify these effects. Shaking table tests allow the study of loading rate phenomenon, however they suffer from difficulties in assessing causality (direct assessment of causes on effects) and are expensive to conduct. An alternative is to test individual RC elements by directly imparting high‐velocity loading protocols. However, multi‐actuator setups are necessary to achieve seismically representative loading and boundary conditions, which entails particularly challenging control requirements. This investigation makes use of recent advances in real‐time testing hardware to study effects of loading rates on the structural response of lightly confined reinforced concrete columns. A pioneering test setup, in which three actuators are controlled independently at high velocities was used to test a series of columns until axial collapse. Experimental challenges and column behavior are discussed.

Select this Article		Development of a Reliability Framework for the Use of Advanced Nonlinear Finite Elements in the Design of Concrete Structures Mehdi Ben Ftima and Bruno Massicotte Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000538 Posted ahead of print 19 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper proposes a methodology that uses advanced nonlinear finite element analysis for determining a global resistance factor for the design of reinforced concrete structures. It introduces a new reliability approach which takes into account the uncertainties of the material properties and the performance of the concrete model used in the calculations. In the proposed approach, the global resistance factor is computed following a procedure in which the coefficient of variation of the calculated resistance is estimated using Rosenblueth's point estimate method. Robustness and simplicity of the method are demonstrated through validation examples. It is seen that good approximations of the resistance factor can be achieved for the case of normal or quasi‐normal distributions of the resistance. Estimation of the coefficient of variation of the prediction error is then performed for a given reinforced concrete element and a nonlinear finite element package. The accuracy of the selected software is considered through its ability of predicting the behaviour of a set of benchmarks selected for the target design structure, going from the material level to the structural level. The suggested methodology is well suited for structural engineers having access to nonlinear deterministic finite element packages with concrete models. It proposes a reliability format that focuses on the variability on the resistance side while using the concept of critical load paths on the load side which is compatible with the philosophy of existing design codes.

Select this Article		Evaluation of Racking Performance of Wood Portal Frames with Different Wall Configurations and Construction Details Chun Ni, Minjuan He, and Songlai Chen Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000537 Posted ahead of print 8 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract The performance of portal frame walls was studied using a finite element model verified with results from tests of full‐size portal frame walls. Parameters such as wall height, metal strap type and location, doubling of the bottom plate, sheathing placement and nailing pattern were investigated. Results indicate that in all cases, lateral load capacity and stiffness are greatly reduced with the increase of wall height. Considering the effect of different metal strap types and locations, the tensile strength of metal straps has the greatest impact on the lateral load capacity and stiffness. Walls with metal straps placed directly on framing members outperform walls with metal straps placed over the sheathing. For walls with a double bottom plate and two rows of nails fastening the bottom plate, the stiffness and lateral load capacity are slightly increased compared to walls with a single bottom plate. For walls with unblocked sheathing at mid‐height, the lateral load capacity is the same as in walls with continuous sheathing running from the bottom of the wall to the top, but the stiffness is slightly lower.

Select this Article		Midply Truss Wall System ‐ A High Performance Shear Wall for Mid‐Rise Wood Frame Buildings Jung‐Pyo Hong, Chun Ni, M. ASCE, and Matt Vinson Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000536 Posted ahead of print 8 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract A high performance wood frame shear wall system, named the MIDPLY Truss Wall (MTW) was developed for application to mid‐rise wood frame buildings. The basic MTW system consists of metal plate connected wood trusses, sheathing panels, and steel tie‐downs. The sheathing panels of the MTW system are placed between the wood trusses, and connected with mechanical fasteners. The main concept of the MTW system is to increase the lateral load resistance of a shear wall by re‐configuring the wall frame members into lateral load resisting wood trusses. In this study, the feasibility of MTW system was investigated. Eight 2,440 mm × 2,440 mm MTW walls were constructed and tested under monotonic and cyclic loading in accordance with test standard ASTM E 2126. Shear stiffness, strength properties and ductility of the MTW walls were evaluated and compared to those of comparable MIDPLY walls. Overall, the MTW system shows significant improvements in shear stiffness, yield load, peak load and ductility. This paper contains a discussion of the failure modes, the effect of vertical load, the importance of truss design and the further studies needed.

Select this Article		A Simplified Beam Model to Estimate Leakage in Longitudinally Cracked Pressurized Pipes Stefano de Miranda, Luisa Molari, Giulia Scalet, and Francesco Ubertini Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000535 Posted ahead of print 8 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract Losses from water distribution systems are reaching alarming levels in many cities throughout the world. Leakage is often the principal cause of water loss due to aging and deterioration of these systems and pressure has been verified to assume a key‐role in water loss management. This paper presents a simple analytical model based on a beam with elastic constraints to estimate the leak area (from which the leakage is then estimated) in longitudinally cracked pressurized pipes and to evaluate the effect of pressure on the opening area of the crack. The model is calibrated on the results of a three‐dimensional finite element analysis and then validated by experimental results. The validation has been carried out for a wide range of pipes made of different materials (PVC, cast iron, asbestos‐cement, and steel) with radii ranging from 27.5 mm to 110 mm and thicknesses from 1.5 mm to 12 mm and crack lengths from 50 mm to 200 mm. The beam model, notwithstanding its simplicity, provides reliable leakage evaluations in longitudinally cracked pressurized pipes.

Select this Article		Discussion on Tension Stiffening in Prestressed Concrete Beams Using Moment‐Curvature Relationship Shobeir Pirayeh Gar, Monique Head, and Stefan Hurlebaus Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000534 Posted ahead of print 3 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract Tension stiffening phenomenon plays a vital role in serviceability of non‐prestressed reinforced concrete (RC) beams as it enhances the post‐cracking flexural stiffness leading to a smaller deflection, accordingly. However, the authors' findings indicate that in contrast to RC sections, the effect of tension stiffening is negligible for fully prestressed concrete sections. Herein, a closed form equation of moment‐curvature for prestressed concrete sections under service load is presented, where the tensile strength of the concrete is taken into account. This equation is verified by experimental test data and numerical analysis, thereby proving the negligible effect of tension stiffening on fully prestressed concrete sections.

Select this Article		Eccentric Axial Load Testing for Concrete‐Encased Steel Columns Using 800MPa Steel and 100MPa Concrete Chang‐Soo Kim, Hong‐Gun Park, Kyung‐Soo Chung, and In‐Rak Choi Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000533 Posted ahead of print 24 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract Seven concrete‐encased steel columns using high‐strength steel (yield strength f_ys = 913MPa and 806MPa) and high‐strength concrete (cylinder compressive strength f_c′ = 97MPa and 113MPa) were tested to investigate the eccentric axial load‐carrying capacity and the deformation capacity. The test parameters were full or partial concrete‐encasement, the eccentricity of axial load, and the effect of lateral reinforcement. Since the yield strain (= about 0.004) of the high‐strength steel is greater than the ultimate compressive strain (= about 0.003) of the concrete, the present study focused on the effect of early concrete crushing on the behavior of the composite columns. The test results showed that in the case of inadequate lateral confinement, the load‐carrying capacity was limited by the early crushing of concrete. However, due to the high‐strength steel section, all test specimens showed ductile flexural behavior after the delamination of the concrete. The test results were compared with the predictions by nonlinear numerical analysis and current design codes.

Select this Article		Generation and Nomenclature of Tessellations and Double‐Layer Grids Valentin Gomez‐Jauregui, Cesar Otero, Ruben Arias, and Cristina Manchado Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000532 Posted ahead of print 24 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract The aim of this work is to establish a systematic methodology for generating automatically different tessellations and double‐layer grids (DLGs) following a defined and specific nomenclature proposed originally for such a task. This particular nomenclature defines the notation of mosaics and DLGs in a synthesized and unique manner, with the advantage that it shows how to generate and design them after the parameters expressed on their own names. As a result, by means of an algorithm and some computational codes, it is possible to recreate in 3D any of those grids directly from their own names. Current nomenclature for tessellations is also analyzed, finding severe disadvantages, such as the excessive length of their notations or their non‐uniqueness character. A new nomenclature is proposed in order to define and generate consistently and unequivocally n‐uniform mosaics in a consistent manner with the current nomenclature used for the Archimedean (regular and semiregular) tessellations.

Select this Article		Experimental Investigation of Self‐Centering Steel Plate Shear Walls Patricia M. Clayton, Tyler B. Winkley, Jeffrey W. Berman, and Laura N. Lowes Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000531 Posted ahead of print 24 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract A series of subassembly tests were conducted to investigate the behavior of the self‐centering steel plate shear wall (SC‐SPSW) system under cyclic loading. The SC‐SPSW system utilizes thin steel web plates to provide energy dissipation and the primary strength and stiffness of the system, while post‐tensioned (PT) beam‐to‐column connections provide recentering capabilities. In this new system, the web plate is intended to yield under cyclic loading, while the boundary elements and PT connection elements remain undamaged. The web plate can then be replaced relatively easily following significant inelastic cycles. This experimental program studies the effects of different design parameters on the system and connection response and compares the response with approximate analytical formulas. The experimental results show that the SC‐SPSW system has high ductility, high initial stiffness, recentering capabilities, an overall system response as anticipated, and more energy dissipation than expected.

Select this Article		The Structural Behavior of Thin‐Walled Metal Silos Subject to Different Flow Channel Sizes under Eccentric Discharge Pressures Adam J. Sadowski and J. Michael Rotter, F. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000530 Posted ahead of print 24 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract The condition of eccentric discharge is known to be one of the most critical for the design of thin‐walled cylindrical metal silos. Significant progress has been made in recent years in devising a relatively realistic set of representative pressures for this load case. However, the consequences these may have on the predicted structural behavior of a silo are not yet fully understood. This paper presents a detailed parametric study into the behavior of a customdesigned slender silo under a set of unsymmetrical pressures describing the action of an eccentric parallel‐sided pipe flow channel of varying cross‐sectional area. The results are compared with the reference axisymmetric case of concentric discharge. It is found that the predicted behavior is very complex indeed, and that geometric nonlinearity is of much greater significance for cylindrical shells under unsymmetrical load patterns than under symmetrical patterns. Further, it is found that eigenmode‐affine imperfections, very deleterious under axisymmetric loading patters, are instead beneficial to the buckling strength of a silo under eccentric discharge, thus making them unsuitable for use in design for this load condition.

Select this Article		Static Cyclic Response of Partially Grouted Masonry Shear Walls Shawn M. Nolph and Mohamed A. ElGawady, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000529 Posted ahead of print 25 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract This research investigated the shear behavior of five full‐scale partially grouted masonry shear walls (PG‐MWs). The walls were built using concrete masonry units and having horizontal reinforcement ratios ranging from 0.085% to 0.169%. The specimens had horizontal spacing between vertical grouted cells ranging from 610 mm (24 in.) to 1219 mm (48 in.). All the specimens were tested under constant gravity load and incrementally increasing inplane loading cycles. This research showed that there appears to be a maximum horizontal reinforcement ratio after which no additional shear capacity is achieved. Based on the experimental results, the maximum value appears to be approximately 0.1% for specimens having horizontal spacing between vertical grouted cells of 1219 mm (48 in.). Increasing the horizontal reinforcement beyond this level did not increase the shear strength of the test specimens. In addition, the current provisions of the Masonry Standards Joint Committee (MSJC), New Zealand Code for Masonry Structures, Fattal's model, and strut and tie model were used to predict the shear strengths of the tests specimens. The current MSJC shear equations over‐estimated the strength of PG‐MWs having horizontal spacing between vertical grouted cells of 1219 mm (48 in.). A significant source of this error is from over‐estimating the contribution of the horizontal reinforcement. In addition, the current MSJC equations overestimated the masonry contribution to the shear strength of PG‐MWs. For partially grouted walls with horizontal spacing between vertical grouted cells of 813 mm (32 in.), or less, and a horizontal reinforcement ratio of 0.085%, the MSJC shear equations are adequate. Shear equations by other codes and researchers were unconservative, as well. The strut and tie models were able to predict the shear strength of the test specimens within ±16%.

Select this Article		Uncertainty Analysis of Flexural Overstrength Ratio for R/C Columns Cem Aydemir and Mustafa Zorbozan Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000528 Posted ahead of print 24 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper summarizes the results of a comprehensive statistical study of flexural overstrength ratio for estimation of probable flexural strength for ductile R/C columns with varying geometries and confinement levels. Material and section properties and analytical model response are modeled as random variables and their effects on section behavior are assessed through statistical evaluation. For randomly sampled values of the considered variables, the sectional analyses are carried out using a computer program which uses various confined and unconfined concrete models to obtain the maximum flexural strength in the moment‐curvature relationship. The effect of variability is investigated by examining response distributions resulting from Monte Carlo simulations. Furthermore, a simple expression is derived for estimation of the probable flexural strength using the flexural overstrength ratio with the 10‐ probability of being exceeded. Finally, the proposed method is compared to ACI 318, Eurocode 8 and Turkish seismic design code provisions.

Select this Article		Multiple‐Tuned‐Mass‐Dampers for Multi‐Modal Control of Pedestrian Bridges Y. Daniel, O. Lavan, M. ASCE, and R. Levy, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000527 Posted ahead of print 24 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper deals with the allocation and sizing of multiple tuned‐mass‐dampers (MTMDs) in an attempt to retrofit footbridges with multiple critical modes resulting from the excitation of pedestrian traffic. The simple and practical methodology proposed herein includes the use of an iterative analysis/redesign type procedure that converges to a given allowable level of accelerations. An example that uses this methodology to retrofit an existing footbridge is presented.

Select this Article		Longitudinal Stiffeners in Concrete Filled Tubes (CFT) Kyoung C. Lee, A. M. ASCE and Chai H. Yoo, F. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000526 Posted ahead of print 20 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract In order to enhance the strength and constructability of rectangular (or trapezoidal) tubular compression members, reinforced or unreinforced concrete may be filled in the tube. Longitudinal stiffeners are often attached to increase the local buckling strength of the thin‐walled skin. The effect of important design parameters on the minimum required stiffener moment of inertia was investigated numerically in this study by examining the residual stress distributions, initial imperfections, and elastic and inelastic buckling stresses of a number of hypothetical models. Since the thin‐walled panel can only buckle (bulge) out from the concrete core, the buckling mode shape of a panel with multiple stiffeners resembles a waffle slab. To characterize and quantify the analytically collected data, a series of parametric studies were performed. A new equation for the minimum required moment of inertia for the longitudinal stiffeners was derived. Through the evaluation of a few selected case studies and a design example, the validity and reliability of the proposed equation is demonstrated.

Select this Article		Elastic Analysis of Beam‐Wall Joints Subjected to Out‐of‐Plane Bending Ying Chen, Zhifei Shi, and Y. L. Mo Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000519 Posted ahead of print 18 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract The mechanical performance of reinforced concrete beam‐thin wall joints under out of plane bending moments is studied and the analytical solutions in terms of stresses and rotational stiffness of the wall are obtained. For convenience, the equivalent bending width of the shear‐walls is introduced and obtained based on two equivalence principles. A detailed parametric study of the equivalent bending width is carried out, including geometric parameters, boundary conditions and reinforcement ratio of the shear‐wall beam joint. Some simplified formulae for the equivalent width are proposed, and compared to both the analytical solutions and the experimental results. Good agreements are found.

Select this Article		Analysis of the Non‐Linear Behavior of Timber‐Concrete Connections A. M. P. G. Dias Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000523 Posted ahead of print 18 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper discusses the non‐linear mechanical behavior of timber‐concrete structures, mainly when dowel‐type fasteners are used in the connections. These non‐linear phenomena result from the non‐linear mechanical behavior of the materials and connections. This paper deals with the connection aspect of the non‐linearity and goes on to present and discuss the causes of such phenomena as well as the approaches available to address them. Since these analyses require an adequate definition of the load‐slip behavior of the connection, a numerical model is proposed to derive it, based on either results from experimental tests or numerical models. A calculation example is used in order to assess the influence of the non‐linear phenomena on the design of this type of structure. From the analysis undertaken, it is concluded that the non‐linear mechanical behavior of the connections may have a significant influence on the mechanical behavior of the composite structures. Moreover, the model proposed to describe the load‐slip behavior of the connection is shown to be accurate and effective.

Select this Article		Equilibrium of Pointed, Circular and Elliptical Masonry Arches Bearing Vertical Walls Danila Aita, Riccardo Barsotti, and Stefano Bennati Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000522 Posted ahead of print 18 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract The paper addresses a long‐standing problem: the equilibrium of the circular, pointed and elliptical arches commonly found in historical masonry buildings and bridges, subjected to their own weight and the weight of superimposed masonry walls. The equilibrium problem is studied by applying two different, complementary methods: the first is a simple extension and analytical re‐reading of the Durand‐Claye stability area method; the second is based on the application of a nonlinear elastic one‐dimensional model, already used by the authors in prior studies. It is assumed that the arch's constituent material has limited compressive strength and null tensile strength. In addition, the load transferred to the arch by the wall is determined under the common assumption that each vertical strip of wall bears directly down on the underlying arch element. The study focuses on the maximum height that the superimposed wall can reach under equilibrium conditions while maintaining acceptable values of arch residual stiffness. One noteworthy finding is confirmation of the decidedly better behaviour of pointed and elliptical flat arches compared to that of the others.

Select this Article		A Finite Element to Calculate the Overall Stiffness of Cracked Reinforced Concrete Beams Arnaud Castel, Thierry Vidal, and Raoul François Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000520 Posted ahead of print 18 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract The Macro‐Finite‐Element (MFE) modeling proposed in this paper is dedicated to the calculation of the deflection of already cracked reinforced concrete beams under service loading at the stabilized cracking stage. MFEs are Beam Finite Elements, characterized by their average moment of inertia, calculated using non‐linear assumed distributions of steel strain, concrete strain and neutral axis between two consecutive bending cracks. The results of the MFE model are successfully compared to experiments performed on five RC‐beams including square‐section and T‐section beams and two concretes (grades 30 MPa and 40 MPa). A successful application of the MFE method to a statically indeterminate beam is also presented. The MFE modeling is appealing for use in practice due to its computational simplicity.

Select this Article		Transverse Joint Details with Tight Bend Diameter U‐Bars for Accelerated Bridge Construction Zhongguo John Ma, Associate Professor, F. ASCE, Samuel Lewis, MS Student, Qi Cao, Ph.D. Student, Zhiqi He, Ph.D. Student, Edwin G. Burdette, Professor, F. ASCE, and Catherine E. W. French, Professor, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000518 Posted ahead of print 18 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper focuses on an investigation of transverse joint details with tight bend diameter U‐bars for accelerated bridge construction. It presents the testing results of potential alternate reinforcing materials and joint details in two phases. Headed bar and U‐bar (stainless steel and deformed wire reinforcement (DWR)) specimens with the same joint detail configuration were tested and compared in the Phase I, followed by testing of U‐bar (DWR) with varied concrete strength, bar spacing, and overlap length in Phase II. Tests results were evaluated based on tension capacity, cracking at service loading and failure, and steel strain. A strut‐and‐tie model is proposed to predict the tension capacity of a transverse joint, which is capable of identifying the most critical parameters and yields safe and consistent predictions. Based on the experimental results, a #5 U‐bar joint detail with no less than 152mm (6 in.) overlap length and #4 lacer bars was recommended.

Select this Article		Timber Frame Moment Joints with Glued‐In Steel Rods. Part 2: Experimental Investigation of Long‐Term Performance Massimo Fragiacomo and Mark Batchelar Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000517 Posted ahead of print 18 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract The pull‐out performance of steel rods glued into timber is well documented, and short‐term tests by many researchers have demonstrated reliable strength. The behavior of glued‐in steel rods in moment‐resisting beam‐column joints is much more complex due to anisotropy of wood in the connection region, discontinuity of material at the interface, and the possible effects of creep of timber and stress concentrations on the joint performance. This paper describes the results of a series of long‐term load tests on moment‐resisting joints between glulam members, together with separate load tests on the various joint components including the epoxy itself and the timber stressed perpendicular to the grain. Different types of knee joints, with rods fully epoxied along their length or epoxied only in one member and tensioned in the other, and with different geometries (with beam extended over the column or with column extended past the beam) were tested. Measurements were recorded to identify time dependant stress redistribution within the test joints, creep of the joint as a whole, and possible crushing of the timber‐to‐timber bearing surfaces. Local deformation of timber loaded in compression perpendicular to the grain was found to contribute to excessive joint deformations in tests where the steel rods were not glued over their full length. The test results confirm the possibility to use the transformed section method in design as presented in the first companion paper, and address a number of issues pointed out in the same paper.

Select this Article		Large Eddy Simulations of Wind‐Driven Rain on Tall Building Facades S. H. Huang and Q. S. Li, M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000516 Posted ahead of print 18 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract Wind‐driven‐rain (WDR) on building facades may lead to water penetration, cladding damage, structural cracking etc., which affect the durability of claddings. This study aims to develop a numerical approach for the evaluation of WDR on tall building envelopes based on large eddy simulations (LES) and Eulerian multiphase model. The present method utilizes the concept of the multiphase model to deal with rain and wind, and both wind and rain motions as well as their interactions are treated under Euler frame, which can significantly reduce the complexity in the evaluations of WDR and simplify the boundary condition treatments. Besides these advantages, unsteady‐state WDR information such as the transient catch ratio of WDR, the spatial and temporal distributions of rain intensity etc. can be predicted by the LES. A validation study shows that the simulation results agree well with available experimental data, verifying the accuracy of the simulation approach based on the Eulerian multiphase model and LES. Furthermore, LES of WDR on the 508 m high Taipei 101 Tower is performed to illustrate the application of the present method and to investigate the WDR on the tall building. Both the transient and the time‐averaged WDR results are presented and discussed, demonstrating that the present approach can provide more information on WDR than existing methods.

Select this Article		Tension Capacity of Staggered Bolted Connections in Cold‐Reduced Steel Sheets Lip H. Teh, A. M. ASCE and Drew D. A. Clements Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000514 Posted ahead of print 26 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper examines the assumption implicit in Cochrane's formula that stresses are uniformly distributed across the net section of a staggered bolted connection. The assumption was found to be overoptimistic for connections in steel having low ductility, leading to unconservative estimates for the tension capacity if the in‐plane shear lag is not accounted for. The reduction factor of 0.9 specified in the North American specification for cold‐formed steel structures partially but not wholly addresses the problems inherent in the code equations. This paper points out that the “simplification” of Cochrane's original formula into the standard formula used in steel design codes worldwide can lead to additional design capacity that may not be justified. It proposes an equation that accounts for the in‐plane shear lag and incorporates Cochrane's original formula for determining the net section area. The proposed equation is demonstrated through laboratory tests on 74 staggered bolted connection specimens in 1.5 mm and 3.0 mm G450 sheet steel to be more accurate and consistent than the code equations in predicting the net section tension capacity.

Select this Article		Seismic Evaluation of Masonry Structures Strengthened with Reinforced Concrete Layers Bahman Ghiassi, Masoud Soltani, and Abbas Ali Tasnimi Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000513 Posted ahead of print 26 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract Coating the walls with reinforced concrete layers is a conventional method of strengthening masonry structures in Iran. However, due to the lack of analytical and experimental information about the behavior of strengthened masonry wall with this method, the design of these walls is generally conducted based on empirical relations and decisions which may result in uneconomical or under‐designed strengthening details. This paper aims at developing a rational method for design and seismic evaluation of unreinforced masonry walls strengthened with reinforced concrete (RC) layers. In the proposed method four failure modes are considered for these walls and the strength relations and acceptance criteria for each of them are provided in accordance with FEMA 356 and ASCE 41 relations for reinforced concrete and masonry walls. The accuracy of the proposed method in predicting the nonlinear behavior and governing failure modes of the strengthened walls is validated by comparing the results with available experimental and performed numerical results.

Select this Article		Impact of Residual Stresses and Initial Imperfections on the Seismic Response of Steel Moment Frames Kapil Mathur, Larry A. Fahnestock, P.E., M. ASCE, Taichiro Okazaki, M. ASCE, and Matthew J. Parkolap Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000512 Posted ahead of print 26 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract The 2010 AISC Specification establishes the Direct Analysis Method (DM) as the standard stability analysis and design procedure. Although the DM has important benefits over conventional stability design methods, the interface between the DM, the AISC Seismic Provisions and the seismic design requirements in ASCE‐7 is not fully established. Since the DM, which was developed for design scenarios that do not contain seismic loading, includes the effects of initial geometric imperfections and inelastic behavior due to residual stresses, it is critical to explore the impact of these parameters on the seismic behavior of typical steel buildings. To examine these issues, a series of steel special moment‐resisting frame models were subjected to monotonic pushover, cyclic pushover and response history analyses. The observed behavior was used to draw comparisons between systems with and without residual stresses and initial imperfections. Cyclic strength degradation at beam‐to‐column connections was also considered to examine the potential interaction it may have with the other parameters. Whereas the well‐known impact of strength degradation on cyclic stability was noted, residual stresses and initial imperfections did not have any appreciable effect on stability behavior for the systems considered. The analyses conducted in this study indicate no clear benefit to using the DM when designing regular ductile steel systems in high seismic regions and simpler design methods may be equally effective.

Select this Article		OpenSees‐SNOPT Framework for Finite Element‐Based Optimization of Structural and Geotechnical Systems Quan Gu, A. M. ASCE, Michele Barbato, A. M. ASCE, Joel P. Conte, M. ASCE, Philip E. Gill, and Frank McKenna Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000511 Posted ahead of print 26 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract The finite element (FE) method is widely recognized as a powerful tool to model structural and geotechnical systems and to simulate their response to static and dynamic loads. In addition, numerical optimization is commonly used in many engineering applications, such as structural reliability analysis, FE model updating, structural identification and structural optimization. This paper focuses on the extension of OpenSees (an existing software framework for nonlinear FE analysis) using SNOPT, a state‐of‐the‐art numerical optimization software. The extended OpenSees‐SNOPT framework is general and flexible and can be used to solve a wide range of FE‐based optimization problems in structural and geotechnical engineering. It has several distinguishing features: (1) advanced capabilities in solving optimization problems involving complex structural/geotechnical engineering systems; (2) versatility to model a very wide range of structural and/or geotechnical systems; (3) computational efficiency; (4) flexibility to easily accommodate and benefit from new developments in FE structural modeling and analysis, computational optimization, and probabilistic modeling and analysis; and (5) capabilities of exploring new optimization‐based problems and solution methods. The use of this coupled framework is illustrated through three representative application examples, i.e., a FE reliability analysis of a reinforced concrete frame, a FE structural optimization problem of an electrical transmission steel tower, and a FE model updating problem of a geotechnical system.

Select this Article		Finite Element Model Updating and Probabilistic Analysis of Timber‐Concrete Composite Beams Alessandro Zona, A. M. ASCE, Michele Barbato, A. M. ASCE, and Massimo Fragiacomo Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000509 Posted ahead of print 26 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract Timber‐concrete composite beams are an increasingly common design solution for medium to long span floors in new buildings. Thus, there is a significant need for accurate models and analysis tools to predict the response and performance of timber‐concrete composite beams. In this paper, a nonlinear finite element (FE) frame model with deformable shear connection is adopted to estimate the short‐term structural response of timber‐concrete composite beams for which experimental results are available. The FE model is used in conjunction with a probabilistic analysis methodology that explicitly accounts for the uncertainties in the parameters describing the constitutive models for timber, concrete, and shear connectors. The objectives of this study are: (1) the evaluation of the variability of global and local structural response quantities due to the uncertainties in the constitutive parameters of timber, concrete, and shear connectors; and (2) the analysis of the correlation between experimental measurements and numerical results based on FE models in which the values of the constitutive parameters are set equal (i) to their experimentally identified mean values, and (ii) to optimized values obtained through FE model updating, respectively. The results presented in this study show that uncertainties in the constitutive parameters of timber, concrete, and shear connectors have a significant influence on the correlation between experimental and numerical results. In addition, the optimal values of material parameters obtained using the FE model updating procedure might show substantial variations with respect to the parameters' mean values as identified in experimental testing. Prospective developments directed toward design applications and based on the obtained results are also discussed.

Select this Article		A Heuristic Approach for Optimum Cost and Layout Design of 3D Reinforced Concrete Frames P. Sharafi, Muhammad N. S. Hadi, and L. H. Teh Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000508 Posted ahead of print 26 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a new methodology for cost optimization of the preliminary layout design of three‐dimensional reinforced concrete (RC) frames. This approach is capable of being easily employed for the optimal layout design of a realistic large RC structure that accounts for constraints imposed by design standards. The new approach considers modeling, structural analysis, concrete member design, and discrete optimization together with data on cost of systems and materials. The methodology comprises two parts. First, using the cross‐sectional action effects as design variables, a heuristic cost function is presented as an alternative to traditional cost functions for layout optimization of RC structures. Using the presented cost function, a structural optimization problem is formulated for column layout design of 3D RC frames. Then, an Ant System (AS) algorithm, a discrete method, is proposed to solve the cost optimization problem. Two comparative design examples are included to demonstrate the performance of the new methodology and the excellent convergence of the Ant Colony Optimization (ACO) algorithm.

Select this Article		Effect of Plastic Constraint on Brittle Fracture in Steel: Evaluation Using Toughness Scaling Model Tsutomu Iwashita and Koji Azuma Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000507 Posted ahead of print 26 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract Over the past two decades, plastic constraint effects have been an issue of concern in both fracture mechanics and structural integrity research, and several methods have been proposed for considering loss of plastic constraint. This paper shows the ability of a simplified model to predict brittle fracture under low plastic constraint conditions. Fracture toughness tests are performed on single‐edge notched bend (SENB) steel specimens with deep and shallow notches, as well as on double‐edge notched tension (DENT) and center‐notched tension (CNT) specimens. When compared with SENB specimens with a deep notch, the CNT specimens show high fracture toughness due to the loss of plastic constraint at the crack tip. Here, the Weibull stress approach and a toughness scaling model (TSM) are used to consider the effects of the loss of plastic constraint on the fracture toughness of the specimens. The corrected fracture toughness values evaluated by the TSM are found to be close to the toughness values observed in the tests and to the values predicted by the Weibull stress approach. This paper also briefly discusses the effect of ductile crack growth on brittle fracture.

Select this Article		P‐Δ and End Rotation Effects on the Influence of Mechanical Properties of Elastomeric Isolation Bearings Ali Karbakhsh, Ismail Othman, Zainah Ibrahim, and Kamarudin Ab‐Malek Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000503 Posted ahead of print 26 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract Seismic isolation systems constitute an accepted and simple technique for earthquake protection of structural systems and sensitive components. This approach has considerable potential in preventing the structures and their equipments from earthquake destruction. For predicting the behavior of an isolation bearing, the Haringx's theory is usually employed. According to this theory, the mechanical properties of an elastomeric isolation bearing can be predicted and described. Many investigators have proposed a nonlinear, mechanical model for multilayer elastomeric bearings. However, in past theoretical and experimental studies, the effects of initial rotation at the ends of the bearings have been neglected. In this study, the Haringx's theory is extended and an analytical method is presented by considering the initial rotations of the upper and lower ends of multilayer rubber bearings as new boundary conditions. Three boundary conditions: 1) equal rotation at the bottom and top end of a bearing, 2) rotation only at the bottom end, and 3) rotation only at the top end of a bearing have been considered for modeling the elastomeric isolation bearing. According to these boundary conditions, variations of the lateral displacement and interior rotation of the laminated rubber bearings are obtained. The variations of horizontal stiffness, internal bending moment and interior shear force of the bearing have also been presented. Examples are presented to demonstrate the validity of the development method in predicting the mechanical properties of elastomeric bearings with specified geometric parameters. The results of this study have shown that initial rotation as a boundary condition will change the mechanical properties of the laminated rubber bearings.

Select this Article		Stability Analysis of Metal‐Plate‐Connected Wood Truss Assemblies Xiaobin Song, M. ASCE and Frank Lam, M. ASCE, P.E. Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000502 Posted ahead of print 26 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a study on the critical buckling load and lateral bracing force of metal plate connected wood truss assemblies. A three‐dimensional finite element method based computer program was developed, calibrated and verified with test results. A preliminary reliability analysis was conducted based on the verified FEM model with consideration of the variation in material properties and the initial out‐of‐plane deflection of compression webs. It was found that the out‐of‐plane rotational stiffness of MPC connections has a significant effect on the critical buckling load and lateral bracing force ratio of MPC trusses. The critical buckling load could be almost doubled on the basis of an ideally pinned compression web, and the lateral bracing force ratio was found to be generally less than 1% from the test results and numerical analysis. Consequently, the currently used 2% rule of thumb for lateral bracing design may be conservative, by overestimating the lateral bracing force, and may lead to oversized bracing members.

Select this Article		Numerical Modelling of Shear Behaviour of Reinforced Concrete Pile Caps Alan G. Bloodworth, Jing Cao, and Ming Xu Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000499 Posted ahead of print 27 August 2011 Full Text: \| Download PDF
	+ -	Show Abstract The application of bending theory based methods and strut‐and‐tie models for the design of pile caps to resist shear is still a subject of debate, with the latest Eurocodes permitting both methods but not giving much guidance as to their use. The former UK design standards for concrete buildings and bridges, recently withdrawn, gave more guidance and it is likely that these methods will continue to be used by designers. However, there is considerable discrepancy between these standards, particularly with regards to the width of cap over which shear enhancement at short spans may be applied, and how much longitudinal reinforcement to take as a tie in the strut‐and‐tie method. Both standards are also seen as conservative. To gain a better understanding of the problem and assess the available design methods, nonlinear finite element analysis has been performed to investigate the shear behaviour of four‐pile reinforced concrete pile caps, under full‐width wall loading. The models were validated against an experimental programme that included an optical photogrammetric method for measuring full‐field displacements. An extensive parametric study was carried out, varying shear span, cap width and reinforcement ratio over a practical range. The conservatism of the UK design standards, and the real shear capacity of the pile caps, were found to be a function of shear enhancement factor and the width of the cap over which shear enhancement is applied. Strut‐and‐tie behaviour was observed in the models, and a commonly used strut‐and‐tie method was found to give fairly good predictions. A modified strut‐and‐tie method is suggested for this particular configuration of a four‐pile cap under full‐width loading, which gives more accurate predictions. This is especially so for samples with large transverse pile spacing where a significant proportion of the longitudinal reinforcement over the width of the cap can be assumed to participate in the yielding ties.

Select this Article		Elastic Solutions for Eccentrically Loaded, Slender, Rectangular Spandrel Beams Bulent Mercan, Arturo E. Schultz, Henryk K. Stolarski, Rafael A. Magaña, and Mathew J. Lorig Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000498 Posted ahead of print 27 August 2011 Full Text: \| Download PDF
	+ -	Show Abstract Spandrel beams in precast concrete buildings are widely used to support double‐tee deck beams, particularly in parking garages. Spandrel beams of deep cross sections, resisting eccentric loads from double‐tee beams, can be susceptible to excessive lateral deformations and serviceability failures before reaching their strength limits. However, closed‐form solutions for estimating lateral deflections in such members are not available in the technical literature. In this paper, approximate analytical solutions for the deflection of beams with thin rectangular sections are derived from second order elastic analysis, and they are proposed for use in estimating maximum lateral deflections in spandrel beams under eccentric and uniformly distributed loads. Continuous lateral support is provided at the elevation of the floor deck to the spandrel beams, thus two cases are considered, one for laterally restrained beams under typical service conditions, and a second for laterally unrestrained beams prior to the establishing the floor deck connections, or if those connections fail prematurely during service or under extreme loading. An equivalent loading method is proposed to obtain the approximate analytical solutions, in which the differential equations of equilibrium governing the problem are simplified by replacing the actual loading in the spandrel beams with a substitute loading. Numerical solutions are also obtained from three‐dimensional finite element analyses and their results are found to be in close agreement with the analytical solutions for two of the three common types of load‐bearing precast, prestressed concrete spandrel beams.

Select this Article		ReLAM: A Nonlinear, Probabilistic Model for the Analysis of Reinforced Glulam Beams in Bending Robert F. Lindyberg, Ph.D., P.E. and Habib J. Dagher, Ph.D., P.E., M. ASCE Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000496 Posted ahead of print 22 August 2011 Full Text: \| Download PDF
	+ -	Show Abstract In conjunction with Willamette Industries, Georgia‐Pacific, Strongwell, and APA‐the Engineered Wood Association, the University of Maine tested ninety FRP‐reinforced glue‐laminated wood (glulam) beams. This study showed that FRP reinforcement ratio of 3% in tension can increase glulam allowable bending stress (F_b) by over 100%. Further, this physical testing was used to verify a nonlinear probabilistic computer model for reinforced glulam, called ReLAM. ReLAM uses Moment‐Curvature (M‐Φ) analysis and Monte Carlo simulation to predict the strength and stiffness of a population of reinforced glulams, requiring as input distributions of lamstock long‐span flatwise‐bending Modulus of Elasticity (E), Ultimate Tensile Stress (UTS), and Ultimate Compressive Stress (UCS). ReLAM output lists reinforced glulam Modulus of Elasticity (MOE) and F_b in terms of the gross cross‐section dimensions, providing beam properties in the same fashion as the current tabulated properties for unreinforced glulams. ReLAM accurately predicted the F_b and MOE for the 90 reinforced glulams tested, demonstrating that it is a valuable tool for the analysis of reinforced glulams with various layups, reinforcing materials, and reinforcing levels.

Select this Article		A Summary Review of GPS Technology for Structural Health Monitoring Seok Been Im, Ph.D., Stefan Hurlebaus, Ph.D., and Young Jong Kang, Ph.D. Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000475 Posted ahead of print 5 August 2011 Full Text: \| Download PDF
	+ -	Show Abstract Over the past two decades, global positioning system (GPS) technology has been developed rapidly and recently applied to civil structures for appropriate monitoring of structural performance. Currently, the GPS technique can only be applied to flexible structures having lower modal frequency ranges and still has remaining issues when it comes to obtaining accurate measurements. However, the application of GPS is promising as a monitoring tool because it can measure dynamic characteristics as well as static displacements in real‐time while the conventional monitoring system using accelerometers cannot measure static and quasi‐static displacements. Furthermore, rapid advancements in GPS devices and algorithms can mitigate erroneous sources of GPS data, and integrated systems using GPS receivers with other supplement sensors are capable of providing rather accurate measurements. Therefore, GPS technology can provide accurate displacements of structures in real time, and stress and strain conditions of the structures can be computed using finite element models and numerical analyses. It is also expected that damage localization and severity can be identified using the dynamic characteristics of structures obtained from GPS. This paper summarizes the use of GPS technology for structural health monitoring..

Select this Article		Seismic Evaluation of Beam‐Column Joints in Older Concrete Exterior Frames Dawn Lehman, John Stanton, and Daniel Alire Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000463 Posted ahead of print 17 June 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper describes an experimental study on beam‐column joints in older reinforced concrete exterior frames subjected to seismic loading. Because joints in pre‐1970s construction were not designed using modern seismic design guidelines, they typically contain no transverse reinforcement and may be subjected to a wide range of levels of joint shear stress demand. In current codes and recommendations for seismic design and evaluation, simple expressions are used typically to design the joint, and a strut‐mechanism approach has been adopted to assess the strength. However, prior and ongoing research has shown that joint behavior is more complicated than implied by these documents and that defining failure by static strength alone is not sufficient to describe performance. A previous experimental research study, conducted by the principal investigators, has demonstrated that the joint response depends on several parameters, including the demand history. To investigate in greater detail the influence of the joint shear stress demand on the response, the research study described herein was conducted. The data from the two programs were then combined to establish probabilistic relationships between joint damage and Engineering Demand Parameters, such as shear stress and strain, and to obtain estimates of joint stiffness for use in the seismic analysis of older structures.

Select this Article		Elastic Stiffness Comparisons between RBS Beams with Either Flange or Web Reductions Yousef Ashrafi and Behzad Rafezy Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000429 Posted ahead of print 25 April 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper compares the elastic stiffness of RBS beams with either flange or web reductions. The former have received considerable attention, but recently the latter have been shown to have superior plastic rotation capacity and energy dissipation characteristics and are generally more amenable to retrofitting strategies. Initially, a closed form elastic stiffness matrix for an RBS beam with web reduction is derived from first principles. Its performance is then compared with its reduced flange counterpart using data that are available in the literature. Differences between the two approaches are highlighted in a small parametric study.

Select this Article		Timber Frame Moment Joints with Glued‐In Steel Rods. Part 1: Design Massimo Fragiacomo and Mark Batchelar Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000419 Posted ahead of print 20 April 2011 Full Text: \| Download PDF
	+ -	Show Abstract Significant evidence based on experimental research exists to give designers confidence in the use of theoretical equations to evaluate the pull‐out strength of threaded steel rods glued into timber. However the mechanism of load transfer through a timber frame moment joint utilizing glued‐in steel rods requires more than understanding simply the tension performance of a glued‐in rod. This paper presents a method of evaluating joint strength for moment and axial forces based on traditional mechanics theory adapted for use with timber. Formulae were derived from first principles for joint configurations, with extended columns or with extended beams, and with different types of construction, i.e. with rods fully glued along their entire length or only glued in one of the two members connected and then tensioned. The design method also considers the effects of time dependent deformation in timber at bearing interfaces and the effects of stress concentrations imposed by the steel rods on the timber. Some open questions which deserve further investigations are highlighted, as well as some possible details to optimize joint performance whilst retaining ease of assembling. The approach provides a methodology for joint design that has been successfully used in many projects.

Select this Article		A Constitutive Model of Circular Steel Tubes and Its Applications in Analysis of Space Structures F. Fan, G. B. Nie, and X. D. Zhi Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000392 Posted ahead of print 12 February 2011 Full Text: \| Download PDF
	+ -	Show Abstract Developed rapidly in the recent thirty years, space structures in the form of reticulated shells are widely used in all kinds of large‐scale public buildings. The performance of the tubular components of the structures is significantly influenced by large deformation and obvious material plasticity encountered in severe earthquakes. The material behavior needs to be considered in the constitutive model. Tests of fifty circular steel tubes were thus conducted under cyclic axial and horizontal loads to derive the rational constitutive model with consideration of material damage accumulation. The results show that the degree of damage depends on parameters of the tubes and the loading history. Finite element model simulating the performance of the steel tubes was then developed incorporating a user‐defined material sub‐routine UMAT encoded with ABAQUS. A generalized constitutive model of circular steel tubes considering damage accumulation was derived by means of the least square method fitting between numerical simulation and experimental results. Using the finite element model, responses of reticulated shells with different parameters under severe earthquakes have been investigated and the characteristic responses at structural failure have been discussed as well. It was found out that the damage accumulation decreases the structural failure load obviously, which needs to be considered in the analysis and design of the structures.

Select this Article		Automatic DR Structural Analysis of Snap‐Through and Snap‐Back Using Optimized Load Increments M. Rezaiee‐Pajand and J. Alamatian Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000285 Posted ahead of print 2 October 2010 Full Text: \| Download PDF
	+ -	Show Abstract In this paper, new schemes are presented for the Dynamic Relaxation (DR) method so that the snap‐through and the snap‐back regions can be traced automatically. These procedures are based on the minimization of the residual force (MRF) and residual energy (MRE), and they are capable of updating the load factor in each DR iteration. The suggested techniques are perfectly automatic. Therefore, they do not require any additional parameters, such as arc‐length, incremental displacement, etc. For numerical verification, some frame and truss structures, all possessing geometrical non‐linear behaviors, are analyzed. Tracing the statical path shows that both the MRF and MRE methods can be used successfully in structures with snap‐through and snap‐back regions. The numerical results indicate that the MRE scheme traces the statical path with a greater number of increments than the MRF. While the jumping probability of the MRE is less than that of the MRF, the analysis time may increase in the MRE. Also, a comparison between the proposed DR methods and arc‐length approach shows that the MRF and MRE procedures can present the limit points with higher accuracy.

Select this Article		Distortional Buckling of Cold‐Formed Steel Shear Wall Studs under Uplift Force Cheng Yu Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000129 Posted ahead of print 8 October 2009 Full Text: \| Download PDF
	+ -	Show Abstract A coldformed steel framed shear wall may fail in shear buckling of the sheathing, local buckling or distortional buckling of the framing member under compression forces, or connection failures. An unusual distortional buckling mode on boundary studs under uplift forces was recently observed in a shear wall test program conducted at the University of North Texas. It was found in monotonic pushover shear wall tests that the flanges of the boundary studs undertaking uplift forces were distorted at the bottom area of the studs near the hold‐down. This paper presents the test program and analysis of the unique distortional buckling mode. The paper also provides procedures for predicting the distortional buckling strength of the boundary studs, as well as the construction details to mitigate the damage by this unexpected distortional buckling mode.

Select this Article		Analysis of Wind‐Induced Clip Loads on Standing Seam Metal Roofs Murray J. Morrison and Gregory A. Kopp Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000118 Posted ahead of print 2 October 2009 Full Text: \| Download PDF
	+ -	Show Abstract The current investigation extends the work of Farquhar et al. (2005) for calculating components and cladding loads for standing seam metal roof clips. Farquhar et al. (2005) found that the ASCE7‐05 wind loads for these clips are conservative, while several other studies (e.g., St. Pierre et al. 2005, Kopp et al. 2005) have shown that the ASCE7‐05 is unconservative when compared to integrated wind tunnel pressure data. The current note resolves this contradiction, showing that the conservatism observed by Farquhar et al. (2005) is primarily due to the fact that the critical clips are not located in the worst aerodynamic region of the roof.

Select this Article		Finite Element Modeling of Nonlinear Behavior of Masonry‐Infilled RC Frames Andreas Stavridis and P. B. Shing Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000116 Posted ahead of print 2 October 2009 Full Text: \| Download PDF
	+ -	Show Abstract The evaluation of the seismic performance of masonry‐infilled reinforced concrete (RC) frames has been a major challenge for structural engineers. This paper addresses pertinent issues on the development and calibration of nonlinear finite element models for assessing the seismic performance of these structures. The modeling scheme considered here combines the smeared and discrete crack approaches to capture the different failure modes of infilled frames, including the mixed‐mode fracture of mortar joints and the shear failure of RC members. A systematic approach is presented here to calibrate the material parameters, and the accuracy of the nonlinear finite element models has been evaluated with experimental data. The comparison of the numerical and experimental results indicates that the models can successfully capture the highly nonlinear behavior of the physical specimens and accurately predict their strength and failure mechanisms. The validated models have been used to assess the sensitivity of the numerical results to the modeling parameters and to identify the critical material parameters through a parametric study.

Select this Article		The Influence of Flexibility on the Fatigue Performance of the Base Plate Connection in High‐Mast Lighting Towers Margaret K. Warpinski, Robert J. Connor, and Ian C. Hodgson Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000114 Posted ahead of print 2 October 2009 Full Text: \| Download PDF
	+ -	Show Abstract This study investigates the effect of base connection geometry on base plate flexibility and the fatigue performance of multi‐sided high‐mast lighting towers. Three parametric studies investigating the effect of base plate thickness, tube wall thickness and anchor rod configuration are discussed in this paper. The results of this study show that of the geometric parameters considered, base plate thickness has the largest influence on the stresses in the tube wall adjacent to the weld toe. By increasing the base plate thickness of the tower, significant improvement to the fatigue life is observed because the maximum stress, and hence stress range, at the base plate‐to‐tube wall thickness is reduced due a reduction in local bending in the tube wall.

Select this Article		Gust‐Front Factor: A New Framework for Wind Load Effects on Structures Dae‐Kun Kwon and Ahsan Kareem Journal of Structural Engineering doi:http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000010 Posted ahead of print 25 February 2009 Full Text: \| Download PDF
	+ -	Show Abstract In comparison with atmospheric boundary layer winds, which are customarily treated as stationary, winds associated with gust‐fronts originating from a thunderstorm/downburst exhibit rapid changes during a short time period which may be accompanied by changes in direction. This introduces nonstationarity both in the mean and the standard deviation of wind fluctuations. In order to realistically capture characteristics of gust‐front winds and their attendant load effects, a new analysis framework is presented which is named here as the gust‐front factor approach. This is akin to the gust loading factor format used in codes and standards world‐wide for the treatment of conventional boundary layer winds. The gust‐front factor expresses a generalized description of the genesis of the overall wind load effects on structures under both gust‐front and boundary layer winds and it reduces simply to the gust loading factor for the case of conventional boundary layer winds. This approach encapsulates both the kinematic and dynamic features of gust‐front induced wind effects on structures which distinguish themselves from those experienced in conventional boundary layer flows, i.e., variation in the kinematics of the velocity profile and its effects on the associated aerodynamics; dynamic effects induced by the sudden rise in wind speed; non‐stationarity of turbulence in gust‐front winds; transient aerodynamics. To facilitate expeditious utilization of this framework in design practice and inclusion in codes and standards, the analysis framework and its workflow is introduced within a web‐based portal. This eliminates the need for an in‐depth understanding of the background within the framework and the need for associated computational effort. The portal has a user‐friendly interface which is available at http://gff.ce.nd.edu, permitting convenient analysis of several design scenarios with a host of potential loading conditions including the current ASCE 7‐05 procedure in boundary layer winds for immediate comparison.