Accurate modeling of joint effects in lattice transmission towers

Abstract

Lattice Transmission towers are vital components of overhead transmission lines which play an important role in the operation of electrical power systems. Accurate prediction of the structural capacity of lattice towers under different failure modes is very important for accurate assessment of the reliability of transmission lines and power grids, and for design of efficient failure containment measures. Traditionally, lattice towers are analyzed as ideal trusses or frame-truss systems without explicitly considering loading eccentricities and slippage effects in bolted joints. Such effects are always observed in full-scale tower tests and introduce great differences in the ultimate bearing capacity and failure modes obtained from classical linear analysis models. In this paper experimental results available from full-scale prototype tests of a single-circuit 110 kV and a single-circuit 220 kV lattice transmission towers subjected to different load cases are presented and compared with those obtained from four series of numerical models that include joint eccentricity effects and different joint slippage models. The numerical simulation results confirm that joint slippage dramatically increases the deformation of the lattice towers, while its influence on load-bearing capacity will vary in different load cases according to the magnitude of vertical loading and the tower failure mode. Results from the pushover nonlinear static analysis of the towers considering both joint slippage and eccentricity are found in agreement with the experimental results. This type of analysis can be used to model joint effects in lattice towers.