Geometric imperfections and ultimate capacity analysis of a steel lattice transmission tower

Abstract

The effect of geometric imperfections on the decrease of the ultimate capacity of transmission towers has not been sufficiently studied. Despite bucking mode-shaped imperfections are commonly used in deterministic imperfection simulation methods, the current efforts still exist many limitations such as unknown worst buckling mode shape or indeterminate modal combination rules, participation coefficients and truncation order of buckling modes. Herein, a new method named eigenmode assembly method (EAM) is proposed based on linear buckling analysis (LBA). In this method, the first three order local buckling modes of each weak position predicted by LBA are assembled in their sequential order. Two full-scale test towers are employed to implement and validate the proposed approach in this study. The effect of discretized element numbers on the buckling mode shape is firstly discussed, then material and geometric nonlinear analysis is conducted for each case of the EAM-based imperfection assembly process. The results indicate that the EAM can obtain a stable reduction factor for the ultimate capacity of the ideal tower structure which benefited from the advantage of horizontal segment of the capacity curve and can accurately predict the failure positions of transmission towers. Finally, the minimum discretized element number, the minimum introduced buckling mode number and the simplified imperfection assembly formula are recommended by parametric analysis.