Failure analysis of transmission line steel lattice towers subjected to extreme loading

Abstract

Abstract: Lattice towers are extensively used in overhead transmission lines, owing primarily to their lightness and cost-effectiveness. The modeling of such structures is usually laborious due to various complex factors including connection eccentricities, rotational stiffness of connections, bolt slippage, among others. Therefore, full-scale tests are usually performed for the qualification of new overhead line supports, which is a time-consuming and expensive process. Numerical models used in practice rely on simplified hypotheses, using linear truss/beam elements assumed to be pin-connected at both ends. Such models are combined with standard design equations to only evaluate the members’ axial capacities. Finite element models involving solid/shell elements are generally more accurate, though, the computational cost of the resulting problems makes it very difficult to evaluate the response of a complete tower. This paper presents an advanced numerical approach using beam elements aimed at predicting the load-bearing resistance of steel lattice towers under static load cases. Such approach will serve not only to verify the design of new towers, but also to understand various phenomena leading to the collapse of towers in the case of premature failures. The proposed model is developed using the finite element package Code_Aster, wherein lattice towers are modeled using spatial beams. The highly nonlinear problem is solved in an incremental way using advanced features to deal with both geometric and material nonlinearities. An example of a lattice tower loaded until failure is presented and compared with analogous experimental test. The effect of different geometric imperfections on the failure is particularly highlighted.