Failure Analysis of a Cruciform-Leg Transmission Line Tower

Design of latticed steel power transmission towers is a challenging task, which involves lengthy modeling and detailing of significant amount of steel members and connections. The tower is analyzed and designed as a space truss and various members of tower are checked for Tension, Compression and Slenderness Ratio. Sometimes, due to unavailability of required sections or economical point of view, single angle sections are replaced by Cruciform Sections (made of two angles connected toe to toe). The cruciform section, when connected with single angle sections, generate bending moments due to eccentric loading at connection on application of loads on tower, which subsequently results failure of the tower. In the present work, a full-scale testing of a 400 kV tower with built-up leg (Cruciform Leg connected with Single-Angle Leg) has been conducted and the behavior of joint on application of loads has been studied. While testing, one of the legs buckled at the connection. The failure pattern of the leg has been validated using FEM analysis, and the reason of failure has been discussed. In order to confirm the quality of steel, mechanical testing of steel used in leg has been carried out using UTM and results have been explained in the papers. The paper also gives some suggestions for the connection of this type of built-up sections used in tower in order to avoid such failures.