Joint Effects on Behavior of Transmission Towers

Abstract

One assumption usually made in transmission‐tower analysis is that the joints are pinned. However this assumption is rarely realized, due to fabrication difficulties. Thus in practice, the tower members may experience secondary stresses that are not included in the analysis. A full‐scale quadrant of the lowermost panel of a transmission tower designed as a pin‐jointed truss is tested according to the Indian Standard Code of Practice, under normal load conditions and the behavior observed. The test result established that the secondary stresses could be significant enough to cause failure of the leg members even under normal working‐load conditions. This paper also deals with the question of whether a transmission tower with secondary braces would be lighter than one designed without these braces. It has been conclusively shown that though the secondary braces increase the number of members, the reduction in stresses in various members leads to a design considerably lighter than the design without these braces. The analysis assumes point joints, whereas the actual tower has bolted connection. This paper brings out the discrepancies between the analysis and actual behavior witnessed during testing.