Member capacity-based progressive collapse analysis of transmission towers under wind load

The wind-induced collapse of transmission towers has raised many concerns. Progressive collapse analysis is recognized as a promising method for the assessment of the collapse-resistant capacity of the transmission tower. The finite element model of an actual transmission tower is firstly built for the analysis, in which the dynamic behavior of the member in failure is taken into account to be in accord with the actual tower collapse. The analysis considering the main design load cases is conducted in advance to determine the case under which the tower has the potential to collapse. The incremental dynamic analysis in association with the explicit time integration algorithm is employed to perform a progressive collapse analysis, where the wind loads are simulated by using the linear filtering method, and the developed failure criterion with axial force and bending moment involved is based on the stability bearing capacity of the members. It is found the tower collapse begins with the horizontal bracing member near the waist. Then, the adjacent members, including the leg members, fail sequentially, and the tower collapses eventually with a shear-type failure. The demand to capacity ratio (DCR) in terms of bearing capacity of the member is defined to quantify the structural behavior, the location of the member that has the potential to fail, and when the initial failure occurs are thereby identified. It is concluded that compared to the member capacity-based analysis, the ultimate strain-based analysis, which is most likely to be an inelastic dynamic analysis permitting a large deformation, may overestimate the bearing capacity of the structure in wind-induced collapse.