A proposed approach for failure analysis of lattice transmission towers considering geometric imperfection effects

Different types of geometric imperfections can be observed in power transmission lattice towers. These imperfections include eccentricity resulting from the utilization of steel angles, joint slippage, initial crookedness, and dimensional tolerances in the cross-section of lattice tower members. These imperfections contribute to intricate structural behavior, particularly in members experiencing compressive forces. A comprehensive examination of geometric imperfections in lattice tower is crucial, yet research in this vital area is limited. Therefore, for proper modeling of these imperfections and better prediction of lattice tower failure capacity, it is necessary to provide a suitable approach in the modeling of the tower. In the present paper, a modeling method has been developed to analyze the failure of lattice towers, considering geometric imperfections effects (such as eccentricity, joint slippage, initial crookedness, and cross-section dimensional tolerances in the members). The results of the proposed modeling method have been compared with the results of a full-scale failure test conducted on a 400 kV tower. The results of the study show that the proposed modeling method, considering the effect of geometric imperfections, provides a suitable prediction of the tower's load-carrying capacity. Also, to investigate the effects of each geometric imperfection, various finite element numerical models were established, and their force-displacement responses were evaluated. The results show that to make an acceptable estimation of the tower failure behavior, it is not enough to introduce geometric imperfections individually into the analysis. Rather, considering the collective effect of imperfections altogether can give an acceptable estimate of the tower's load-bearing capacity.