Behaviour of novel blind-bolted joints with different strengthening components

Steel-concrete composite structures with concrete-filled steel tubular (CFST) columns have been widely used for multi-storey and high-rise buildings owing to their high structural efficiency and significant economy. Because of the difficulty of accessing the inside of the hollow section, emerging technology using blind bolts has been recently developed for fabricating connections to CFST columns. However, two issues limit the structural benefits of this joint system including the limited transfer of hogging moment and high susceptibility of the steel tube to local failure. Therefore, the authors proposed four different strengthening methods for the CFST column, namely, using inner binding bars, welding two internal rings, externally welding two C-shaped channels, and internally embedding a short segment of I-section in the steel tube. A total of 6 blind-bolted joints were tested under cyclic loading accordingly. The experimental results are analysed in this paper to evaluate the efficiency of different strengthening methods. It indicates that the C-shaped channels and embedded I-section are very effective in enhancing the performance of the joint, and its strength and deformation capacity can be significantly improved with large bending deformation developed in the end plate.