Nonbuilding and Special Structures
Transmission tower systems are susceptible to failures due to extreme wind excitations. This paper focusses on characterizing the failure mechanisms occurring in transmission towers systems by developing the aerodynamic loads using an empirical approach and conducting finite element analysis of the towers considering the nonlinearity of elements. For this purpose a scaled model of the transmission tower is tested under a tornado simulator at the Iowa State University tornado simulator and the data obtained from the simulator is used to verify the loads occurring on the transmission tower during the wind event which were obtained by using the analytical approach. The aerodynamic loads on a sample 500-kv transmission tower is evaluated as the sum of the force on each individual member rather than using conventional methods accounting for the overall truss through solidity ratio and global shielding coefficients. The velocity profile of the horizontal velocity with height is calculated at the tower location as the tornado translates in different tracks. The results from the wind drag coefficients of a single cylinder are used to determine the aerodynamic force coefficients and the velocity profiles. An empirical method was developed in order to calculate the wind forces on lattice tower based on the forces acting on each individual members and considering the shielding effect. The results from the empirical approach show good agreement with those collected from the experiments. This provides an opportunity to more accurately account for the loads induced by tornados on the open structures such as transmission towers.