Improved progressive collapse resistant behavior of steel beam - CFST column connections with energy-dissipating rebars

Progressive collapse is a critical failure mode in framed structures, particularly when a ground-level column fails. Concrete-filled steel tube (CFST) columns are widely used in multi-story and high-rise buildings due to their high axial load-bearing capacity and ease of construction. Fully bolted splice connections between CFST columns and steel beams eliminate the need for high-altitude welding, making them a preferred choice for high-rise structures. However, the presence of splice plates and bolt holes can weaken the connection and reduce its ductility to progressive collapse. This study investigated the progressive collapse resistance of CFST column–steel beam sub-assemblages with fully bolted splice connections through experimental testing and numerical simulations. On this basis, a ductility-enhanced connection was proposed by incorporating energy-dissipating rebars (EDBs) into the splice connection. The EDBs are installed using a series of screw nuts, eliminating the need for welding. The performance of the improved connection was compared with a conventional bolted connection through both physical testing and finite element analysis. Results indicate that the vertical load resistance of the beam-column sub-assemblage progresses through distinct stages, including the friction phase and tensile catenary action. The sub-assemblage reaches peak resistance upon the fracture of the bottom cover plate. Recommendation to enhance the connection performance is given with respect to the ratio of the net section plastic modulus of the cover plates to the I-beam section. Incorporating EDBs shifts plastic deformation away from the bolt hole region, delaying bottom cover plate fracture and enhancing connection ductility. The effectiveness of EDBs is influenced by their cross-sectional area and layout. Maximum ductility is achieved by symmetrically positioning two EDBs at the top and bottom of the beam on each side of the beam web. These findings provide valuable insights for improving the resilience of CFST structures against progressive collapse.