Journal of Structural Engineering

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December 2002

Volume 128, Issue 12, pp. 1491-1630

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Editor's Note

C. Dale Buckner, Editor

J. Struct. Eng. 128, 1491 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1491) (2 pages)

Online Publication Date: 15 November 2002

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Prestressing with Unbonded Internal or External Tendons: Analysis and Computer Model

Nihal Ariyawardena and Amin Ghali, F.ASCE

J. Struct. Eng. 128, 1493 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1493) (9 pages) | Cited 7 times

Online Publication Date: 15 November 2002

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A method of analysis is presented to predict the behavior of prestressed concrete structures with internal or external tendons up to ultimate. The structure is modeled as an assemblage of plane frame members connected at nodes. The prestressing tendon is treated as a member with a small moment of inertia connected to the structural nodes with short arms. Because the centroidal axis changes with cracking and time-dependent effects, the nodes are located on an arbitrarily chosen axis called the reference axis. The analysis includes the effects of tension stiffening, and geometric and material nonlinearities. Any nonlinear stress–strain relationship for concrete and reinforcements can be applied. The analysis accounts for friction and slip of external tendons at deviators, variation of tendon eccentricity with applied load (geometric nonlinearity), and opening of joints in precast segmental construction. The computer program developed to perform the analysis method is verified using experiments on simple and continuous beams with internal or external tendons.

Finite-Element Bond-Slip Model for Concrete Columns under Cyclic Loads

Claire Girard and Josée Bastien

J. Struct. Eng. 128, 1502 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1502) (9 pages) | Cited 4 times

Online Publication Date: 15 November 2002

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The hysteretic behavior of reinforced concrete structures depends in large measure on the transfer mechanism between reinforcing steel and concrete through bond and the resulting slip. This paper presents a finite-element model developed to investigate the response of reinforced concrete columns subjected to cyclic loading, considering in an explicit way the relative displacement at the interface. The novel aspect of the model is its capability of modeling three-dimensional effects as concrete confinement, the softening response of concrete, and to take into account the gradual deterioration of the bond between reinforcing bars and concrete. Numerical results are compared to experimental results on rectangular bridge columns with lapped starter bars subjected to cyclic loading. The numerical model reproduces the physical phenomena observed experimentally, as the gradual stress transfer from one bar to the other. The numerical results show the effect of damage in concrete on the steel stress distribution, as long as the coupled effect of damage in concrete and bond-slip constitutive law on the general behavior of the structural element.

Concrete Constitutive Relationships Under Different Stress-Temperature Paths

Xudong Shi, Teng-Hooi Tan, Kang-Hai Tan, and Zhenhai Guo

J. Struct. Eng. 128, 1511 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1511) (8 pages) | Cited 1 time

Online Publication Date: 15 November 2002

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The behavior of concrete exposed to fire is highly influenced by stress-temperature path. Any stress-temperature path consists of two basic paths: the path of constant temperature but subjected to increasing stress (TS path), and the path of constant stress but subjected to elevated temperature (ST path). The concrete mechanical strain for the TS path can be obtained experimentally, but it is difficult to obtain the mechanical strain for the ST path due to nonuniform temperature distribution within the concrete specimen. In this paper, through analyzing the stress versus mechanical strain curves of concrete from test results for the TS path, a new concept, known as the “temperature-flow mapping” method, is proposed. Based on this concept, temperature versus mechanical strain relationships of concrete for the ST path can be obtained from those curves for the TS path. Mathematical expressions for the concept are also given in the paper. It is found that the predictions based on this concept are in good agreement with experimental results.

Strength Prediction for Discontinuity Regions by Softened Strut-and-Tie Model

Shyh-Jiann Hwang and Hung-Jen Lee

J. Struct. Eng. 128, 1519 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1519) (8 pages) | Cited 10 times

Online Publication Date: 15 November 2002

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Discontinuities caused by abrupt changes in cross-sectional dimensions or by concentrated loads result in discontinuity regions due to disturbance in the flow of internal forces. A simplified method, based on the softened strut-and-tie model, for determining the shear strength of discontinuity regions failing in diagonal compressions is proposed in this paper. Strength predictions of the resulting expressions correlate well with the 449 test results of deep beams, corbels, squat walls, and beam-column joints available from the literature. The proposed method incorporates the shear resisting mechanisms as postulated by the softened strut-and-tie model, and it is a function of the concrete strength, horizontal shear reinforcement, vertical shear reinforcement, and geometrical configuration of the discontinuity regions. A numerical example is included for illustration.

Shear Strength of Reinforced Concrete Columns Strengthened with Carbon-Fiber-Reinforced Plastic Sheet

Lieping Ye, Qingrui Yue, Shuhong Zhao, and Quanwang Li

J. Struct. Eng. 128, 1527 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1527) (8 pages) | Cited 4 times

Online Publication Date: 15 November 2002

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Seven specimens were tested to investigate the shear strength of reinforced concrete (RC) columns strengthened by wrapping with a carbon-fiber-reinforced plastic sheet. All specimens were tested under lateral reversal cyclic loading and a constant axial load. The main parameters considered were the carbon-fiber-reinforced plastic (CFRP) sheet amount, the shear span/depth ratio, and the axial load ratio. Many strain gauges were attached to the CFRP sheet to obtain its shear contribution. It was found that the shear behavior of the RC part of the strengthened column was almost the same as that of the unstrengthened one. The parameters were found to have an influence on the shear contribution of the CFRP sheet, which could be explained by truss-arch shear resistance mechanism. A simple superposition method is suggested to calculate the shear strength of the strengthened column, in which a shear coefficient (ν) is proposed to evaluate the shear contribution of the CFRP sheet based on the test results. The calculated results of suggested method are shown to be in reasonable agreement with test ones.

Compressive Behavior of Carbon Fiber Reinforced Polymer-Confined Concrete in Elliptical Columns

J. G. Teng and L. Lam

J. Struct. Eng. 128, 1535 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1535) (9 pages) | Cited 19 times

Online Publication Date: 15 November 2002

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Reinforced concrete columns can be strengthened by a fiber-reinforced polymer (FRP) jacket which provides lateral confinement to the column. This technique is very effective for circular columns, but its effectiveness is much reduced for rectangular columns. One possibility to increase the effectiveness of FRP confinement for a rectangular column is to modify the column section into an elliptical section. For such section modification to be widely adopted in practice, it is necessary to develop a good understanding of the behavior of FRP-confined concrete in elliptical columns. This paper therefore presents the results of an experimental study on FRP-confined concrete in elliptical columns. Test results are first presented, which indicate that although the confining FRP becomes increasingly less effective as the section becomes more elliptical, substantial strength gains from FRP confinement can still be achieved even for strongly elliptical sections. The ultimate axial strain of the confined concrete is also shown to increase as the FRP confinement becomes stronger. Based on the test results, a simple compressive strength model for FRP-confined concrete in elliptical columns is proposed, in which the effect of the section shape is taken into account by a shape factor.

Stud Shear Connection Design for Composite Concrete Slab and Wood Beams

Piero Gelfi, Ezio Giuriani, M.ASCE, and Alessandra Marini

J. Struct. Eng. 128, 1544 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1544) (7 pages) | Cited 10 times

Online Publication Date: 15 November 2002

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The stiffening and strengthening of wood floors with a thin collaborating concrete slab is a recent technique which appears particularly suitable for restoration work on ancient buildings. This research deals with the theoretical evaluation of the stiffness and strength of the connection between the wooden beam and the concrete slab. Toward this end, both the stiffness and the strength of the connection between the wooden beam and the concrete slab are theoretically assessed. The aim of the present research work is to define a simplified approach which allows the connection design to be based on deformation control. The stud connection is studied in the general case of wooden planks separating the concrete slab and the wooden beam. The initial stiffness of the connection is evaluated on the basis of the classical approach of the beam on elastic foundation, whereas the ultimate strength is based on the collapse mechanism with two plastic hinges in the stud shank. The failure mechanism leads to the definition of the minimum stud length. The results of the theoretical formulation are in good agreement with experimental results.

Effect of Vertical Motions on Seismic Response of Highway Bridges

Martin R. Button, P.E., M.ASCE, Colman J. Cronin, and Ronald L. Mayes, M.ASCE

J. Struct. Eng. 128, 1551 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1551) (14 pages) | Cited 9 times

Online Publication Date: 15 November 2002

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Results of a parametric study of the effects of vertical motions on the seismic response of typical highway bridges are presented. Six different bridges covering a variety of types and geometry are subjected to a suite of ground motions representing events with magnitudes of 6.5 and 7.5 at both rock and soil sites, and with fault distances of 1, 5, 10, 20, and 40 km. Response spectrum analyses are performed on all six bridges for all ground motion parameters. Response results excluding and including vertical motions are compared, with the effect of the vertical motion expressed as a ratio of the dead load actions. Three of the bridges are also analyzed using linear time history analysis to validate the response spectrum results. Analysis of one bridge is extended to incorporate nonlinear behavior of the piers. Recommendations are made for including the effects of vertical ground motions in a code format, and will be considered for adoption by AASHTO in May 2003.

Robust Building Stiffness Design for Variable Critical Excitations

Izuru Takewaki, M.ASCE

J. Struct. Eng. 128, 1565 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1565) (10 pages) | Cited 3 times

Online Publication Date: 15 November 2002

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See Also: Erratum

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Since earthquake ground motions involve various intrinsic and epistemic uncertainties, it is difficult even with the present knowledge to predict forthcoming events at a specific site in a reasonably accurate way. It is therefore desirable to develop a robust structural design method taking into account these uncertainties even partially. Critical excitation or worst-case analysis approaches are making remarkable progress recently and seem to be promising as a candidate to overcome such difficulties. In this paper, the power (area of power spectral density function) and the intensity (magnitude of power spectral density function) are fixed and the critical excitation is found under these restrictions. A design problem for restricted variable design earthquakes is formulated as a minimum–maximum problem which is expected to lead to the maximum global performance design for variable critical excitations. The elastic–plastic response characteristics of the building models designed by the present method are revealed for a broader class of excitations and code-specified design earthquakes.

Collapse Analysis: Large Inelastic Deformations Analysis of Planar Frames

Mettupalayam V. Sivaselvan, S.M.ASCE and Andrei M. Reinhorn, F.ASCE

J. Struct. Eng. 128, 1575 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1575) (9 pages) | Cited 11 times

Online Publication Date: 15 November 2002

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In an attempt to trace the collapse of structures in seismic events, this paper discusses an alternative approach to the formulation and solution of the large deformation inelastic problem in planar frame structures. A beam–column element that includes the effect of geometric and material nonlinearities is developed using the flexibility approach. The formulation uses force interpolation functions and the principle of virtual forces in rate form. It is formulated in the context of the state space approach, where the global system of conservation equations and the local constitutive equations are solved simultaneously. The differential-algebraic system solver is used to solve the resulting system of equations. Numerical examples are presented to illustrate the functionality of the analysis using the newly formulated approach.

Advanced Analysis for Performance-based Design of Steel Structures Exposed to Fires

J. Y. Richard Liew, M.ASCE, L. K. Tang, and Y. S. Choo, M.ASCE

J. Struct. Eng. 128, 1584 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1584) (10 pages) | Cited 4 times

Online Publication Date: 15 November 2002

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This paper presents an advanced plastic hinge analysis method that can be used to assess the performance of steel structures exposed to fire. The main feature of the analysis is to use as few elements as possible to model each structural member and to obtain a realistic representation of the global nonlinear effects of the structure. Natural fires are simulated using the proposed multizone and radiation models. The transient heat transfer is computed using a finite element method. Bounding surface theory is employed to allow for gradual plastification of steel cross sections. Performance-based assessments are carried out on a multistory car park structure and an arched frame exposed to localized car combustion. The effects of beam span, fire source location, and fire spread on the structural behaviors are investigated.

Database-Assisted Wind Load Capacity Estimates for Low-Rise Steel Frames

Seokkwon Jang, Le-Wu Lu, M.ASCE, Fahim Sadek, M.ASCE, and Emil Simiu, F.ASCE

J. Struct. Eng. 128, 1594 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1594) (10 pages) | Cited 3 times

Online Publication Date: 15 November 2002

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A comparative study is presented of the estimated wind load capacities of low-rise steel building frames based on loading patterns (magnitude and distribution) established from aerodynamic databases on the one hand, and on patterns specified in the ASCE 7 Standard on the other. The estimated capacities are based on the assumption, verified by numerous sets of calculations, and also used in the development of the ASCE 7 Standard, that the most unfavorable wind load occurs at the instant in time when the peak knee-joint bending moment is attained. The estimates are obtained from detailed inelastic finite element analyses of the frames with ultimate states associated with local and global instabilities. It is shown that the estimates based on the aerodynamic database are more realistic and risk consistent and can therefore lead to safer designs at lower costs. These estimates represent a significant advance over the ASCE 7 Standard-based estimates.

Alternative Approach for Free Vibration of Beams Carrying A Number of Two-Degree of Freedom Spring-Mass Systems

Jia-Jang Wu

J. Struct. Eng. 128, 1604 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1604) (13 pages) | Cited 5 times

Online Publication Date: 15 November 2002

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The purpose of this paper is to determine the natural frequencies and mode shapes of beams carrying any number of two-degree of freedom (DOF) spring-mass systems by means of two finite element methods FEM1 and FEM2. For convenience, a beam without attachment is called the unconstrained (or bare) beam and that carrying attachment(s) is called the constrained (or loading) beam. FEM1 is the conventional finite element method (FEM), in which each two-DOF spring-mass system is considered as a finite element and then the assembly technique is used to establish the overall property matrices of the constrained beam. FEM2 is an alternative approach, in which each two-DOF spring-mass system is replaced by four effective springs with spring constants keff,ij(v) (i,j = 1,2) and then the overall property matrices of the constrained beam are obtained by considering the whole structural system as the unconstrained beam elastically supported by the effective springs. Based on the above-mentioned two approaches, the eigenvalue equations for the constrained beams are obtained and free vibration analyses are performed. The theoretical and numerical analyses in this paper reveal that the so-called exact solution reported in the existing literature is available only for the case of neglecting the effects of the coupling effective spring constants (i.e., the coupling terms), keff,12(v) and keff,21(v). In other words, the existing exact solution is only a special case of FEM2 presented in this paper.
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Finite Segment Method for Shear Lag Analysis of Cable-Stayed Bridges

Q. Z. Luo, J. Tang, and Q. S. Li

J. Struct. Eng. 128, 1617 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1617) (6 pages) | Cited 2 times

Online Publication Date: 15 November 2002

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Using the principle of minimum potential energy, this paper established the governing differential equations for shear lag in cable-stayed bridges under combined axial and lateral loads. Then the homogeneous solutions of the differential equation for the shear lag are taken as the displacement patterns of the finite segment and applied to calculate the shear lag effect in cable-stayed bridges. The model tests of a box girder are conducted and numerical analysis of the model by the finite strip method are made for comparison purposes. These results verify the accuracy of the present method. The advantage of this approach, compared with the finite element and finite strip methods, is that it can simplify a three-dimensional structure as a one-dimensional structure such as a beam and therefore reduce computational efforts significantly.
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Discussion of “Prediction of Ultimate Shear Strength of Reinforced-Concrete Deep Beams Using Neural Networks” by A. Sanad and M. P. Saka

Sundaramoorthy Rajasekaran, M.ASCE and R. Amalraj

J. Struct. Eng. 128, 1623 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1623) (2 pages) | Cited 2 times

Online Publication Date: 15 November 2002

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Discussion of “Prediction of Ultimate Shear Strength of Reinforced-Concrete Deep Beams Using Neural Networks” by A. Sanad and M. P. Saka

A. T. C. Goh

J. Struct. Eng. 128, 1624 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1624) (1 page)

Online Publication Date: 15 November 2002

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Closure to “Prediction of Ultimate Shear Strength of Reinforced-Concrete Deep Beams Using Neural Networks” by A. Sanad and M. P. Saka

A. Sanad and M. P. Saka, M.ASCE

J. Struct. Eng. 128, 1624 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1624.2) (2 pages)

Online Publication Date: 15 November 2002

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Review of Construction in cities: Social, environmental, political and economic concerns by Patricia J. Lancaster

Kurt H. Gerstle

J. Struct. Eng. 128, 1626 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1626) (1 page)

Online Publication Date: 15 November 2002

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Reviewers

J. Struct. Eng. 128, 1627 (2002); http://dx.doi.org/10.1061/(ASCE)0733-9445(2002)128:12(1627) (4 pages)

Online Publication Date: 15 November 2002

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