Elsevier

Thin-Walled Structures

Volume 41, Issues 2–3, February 2003, Pages 167-177
Thin-Walled Structures

Numerical simulation of structural behaviour of transmission towers

https://doi.org/10.1016/S0263-8231(02)00085-XGet rights and content

Abstract

Transmission towers are a vital component and management needs to assess the reliability and safety of these towers to minimise the risk of disruption to power supply that may result from in-service tower failure. Latticed transmission towers are constructed using angle section members which are eccentrically connected. Factors such as fabrication errors, inadequate joint details and variation of material properties are difficult to quantify. Consequently, proof-loading or full-scale testing of towers has traditionally formed an integral part of the tower design. The paper describes a nonlinear analytical technique to simulate and assess the ultimate structural response of latticed transmission towers. The technique may be used to verify new tower design and reduce or eliminate the need for full-scale tower testing. The method can also be used to assess the strength of existing towers, or to upgrade old and aging towers. The method has been calibrated with results from full-scale tower tests with good accuracy both in terms of the failure load and the failure mode. The method has been employed by electricity utilities in Australia and other countries to: (a) verify new tower design; (b) strengthen existing towers, and (c) upgrade old and aging towers.

Introduction

Overhead transmission lines play an important role in the operation of a reliable electrical power system. Transmission towers are a vital component and management needs to assess the reliability and safety of these towers to minimise the risk of disruption to power supply that may result from in-service tower failure. One of the problems facing tower designers is the difficulty in estimating wind loads as they are based on a probabilistic approach. Another is tower strength, which in contrast, could be deterministic provided a proven-reliable analytical tool is available for the specified design load conditions. In practice, factors such as fabrication errors, inadequate joint details and variation of material properties are difficult to quantify and they are often used to justify the use of full-scale tower testing. Strictly speaking, however, test results are only valid for the particular tower under the particular test loading conditions, and they may not predict exactly how a tower may behave in practice under different loading conditions.

This paper describes a computer simulation technique for predicting the ultimate structural behaviour of self-supporting and guyed latticed transmission towers under static loading. The technique can predict accurately the failure load and the failure mode of towers, and may thus be used to replace or reduce the need to carry out full-scale tower testing. The method has been employed by electricity utilities in Australia and other countries to: (a) verify new tower design; (b) strengthen existing towers, and (c) upgrade old and aging towers.

Three case studies are presented: (i) a calibration case study, (ii) a case study involving the strengthening of existing towers, and (iii) a case study involving upgrading old towers. For commercial reasons, ownership of the towers will not be revealed.

Section snippets

Current analytical techniques

Latticed transmission towers are constructed using angle section members which are eccentrically connected. Towers are widely regarded as one of the most difficult form of lattice structure to analyse. Consequently, proof-loading or full-scale testing of towers has traditionally formed an integral part of the tower design. Stress calculations in the tower are normally obtained from a linear elastic analysis where members are assumed to be axially loaded and, in the majority of cases to have

Nonlinear analytical techniques

In the proposed nonlinear analytical technique, the tower is modelled as an assembly of beam-column elements. Linear, geometric and deformation stiffness matrices are used to describe the behaviour of a general thin-walled beam-column element in an updated Lagrangian framework. This approach greatly reduces the number of elements required (Albermani and Kitipornchai [3], [4]) for accurate modelling of the nonlinear structural response. A lumped plasticity approach coupled with the concept of a

Case study 1: verifying new tower design

A new 330 kV double circuit suspension tower was designed and tested to failure in Australia. The nonlinear analysis was used to verify the design and plan the test sequence prior to the full-scale testing. The tower is shown in Fig. 1. It has a square base of 12.68 m×12.68 m and a height of 53.4 m. The self-weight of the tower was 132 kN. Eight loading conditions were specified for the tower. The tower response was described in terms of a load factor, λ, which is the ratio of the applied load

Conclusion

The paper describes a nonlinear analytical technique for simulating the ultimate structural response of latticed transmission towers. Accurate structural analysis of towers is complicated because the structure is three-dimensional and comprised of angle section members eccentrically connected. The influence of geometric and material nonlinearities plays a very important role in determining the ultimate behaviour of the structure. The proposed technique may be used for verifying new tower design

Acknowledgements

The work described in this paper has been partially supported by a grant from City University of Hong Kong (Project No. 9030875).

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