Experimental Study on the Mechanical Behavior and Failure Mechanism of a Latticed Steel Transmission Tower

Transmission tower collapses caused by strong winds or severe freezing rains frequently occur in many parts around the world. To study the mechanical behavior and failure mechanism of tower structures under such environmental loads, three pairs of tower subassemblages, including one single-panel pair and two double-panel pairs, were designed and statically tested at Tongji University. The difference between the two specimens in each pair was that one had an additional diaphragm as a method of retrofitting while the other did not. One pair of double-panel specimens was tested to simulate and capture the failure pattern of transmission towers subjected to wind load. Correspondingly, two pairs were used to investigate the relevant response of structures under the combination of vertical ice and wind loads. A comparative study on strains at critical sections and local and global deformations as well as failure modes of the tower subassemblages was carried out. The favorable effects of adding the diaphragm, in terms of improving the structural performance of the tower subassemblages, were emphasized in the study. The test results showed that the complex interaction between the main legs and the diagonal bracing members significantly affect the overall stability performance of the towers and their behavior at the ultimate limit state. The study demonstrated that the diaphragms comprehensively improved the mechanical behavior and increased the load-carrying capacity of the transmission tower structures. For specimens subjected to simulated wind load only, the bearing capacity increased by 22.1% after adding horizontal diaphragms. On the other hand, for double- and single-panel specimens subjected to simulated ice and wind loads, the corresponding increases were 17.6 and 18.3%, respectively. The implications of the test results and their relevant practical applications in the wind- and ice-resistant design of transmission towers are summarized and discussed in this paper. (C) 2013 American Society of Civil Engineers.