Reproduction tests and analyses concerning bolt loosening and drop at brace member joints of the transmission tower

Abstract

After the 2011 off the Pacific coast of Tohoku Earthquake, bolt loosening at brace member joints was found out during the inspection of transmission towers. As the shear bolted joint is allowed the bolt slip, the bolt loosening doesn't influence load bearing performance of transmission tower structures immediately. However, if a lot of bolt drop occurs because of the loading history after the bolt loosening, the possibility of load bearing shortage may be caused. In this paper, we conducted bolt loosening and bolt drop reproduction tests, and examined a numerical model and the procedure to analyze the rotation of bolt while considering the experimental bolt loosening behavior. And we summarize some findings concerning the bolt loosenig and drop based on the investigation results.