Transmission assets of most utilities are being required to transfer greater loads than previously anticipated. Difficulty in obtaining new Rights of Way has tasked utilities with increasing the transfer of power using existing assets. Numerous transmission lines composed of latticed towers are being considered for installation of larger conductors or higher line loads requiring greater line tensions to maintain minimum ground clearance. At the same time utilities are replacing existing shield wires with fiber optic systems as well as adding antenna systems at site specific locations. These assets are now being pushed beyond their original design conditions and often times will now exceed the design limits imposed by the current standards. The American Society of Civil Engineers (ASCE) Standard "Design of Latticed Steel Transmission Structures", ASCE 10-97 (ASCE 10-97) provides recommendations for new designs that at times are not met by existing towers. This paper discusses the key issues that must be addressed by both the engineer and utility during the upgrade/uprate process on older steel transmission towers. Suggested guidelines for existing towers will be presented to deal with issues on slenderness ratio limits, minimum edge distances, bolt shear capacities for unknown bolt types, bearing capacities of bolts and members, use of tower test data in the upgrading/uprating process, and member use ratios which exceed 100% of the member capacity. Also included is a brief discussion of bars used as tension-only members, man-loads on horizontal members, and minimum support requirements of redundant members. A brief discussion on the original compression formulas used in older tower designs and ASTM material specifications in older towers in older towers is also included.
Guidelines for Upgrading/Uprating Existing Latticed Transmission Structures
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Electrical Transmission in a New Age Conference
Guidelines for Upgrading/Uprating Existing Latticed Transmission Structures
Robert E. Nickerson, M.ASCE
Abstract
Author
Consulting Engineer, 4101 Crestview Drive, Fort Worth, Texas 76103
Published online: April 26, 2012
Electrical Transmission in a New Age Conference
September 9-12, 2002 | Omaha, Nebraska, United States
© 2002 American Society of Civil Engineers