Behaviors of one-side bolted T-stub through thread holes under tension strengthened with backing plate

Tests were carried out to investigate the one-side bolted T-stub through thread holes under tension strengthen with backing plate. For the thread length is limited by the flange thickness of T-stub, which might lead to the premature failure of the connection due to the failure of thread. The thread length could be increased by adding a backing plate. Two new failure models of the bolted T-stub were proposed to consider the potential failure of hole thread. And the design methods for tension strength of corresponding failure modes were presented. Studied parameters included the bolt pre-tension force and the T-stub flange thickness. The bolt pre-tension force almost did not affect the tension strength of a bolted T-stub, while the initial stiffness could be improved. Effects of the backing plate on the tension strength and load-displacement curve of T-stub under tension were presented through comparing those without backing plate. Test results showed that the backing plates could be efficiently improve the tension strength of the T-stubs. However, for T-stubs with same screw depth, it was more efficient to increase the flange thickness directly. The comparison between test results and calculated results from design methods indicated that the proposed design methods could be used to predict the tension strength and failure modes of the one-side bolted T-stub through thread holes and strengthened with screwed backing plates. Under the design load, the bolted T-stub was still in elastic state, which could meet the design requirement.