Dynamic responses of CFST column to steel beam joints subjected to impact loading

To investigate the dynamic responses of CFST column-to-steel beam joints under impact loading, drop-hammer impact tests were conducted on five semi-scaled beam-column joint specimens simulating the joint region of a frame structure after intermediate column removal. The test parameters included connection configuration, slab effect, impact velocity, and impact sequence. The damage mode, impact force, displacement response, acceleration, strain development, and energy absorption were obtained and compared. Results demonstrated that the fully welded joint exhibited superior impact resistance, with the welded-bolted configuration suffering a severe tensile fracture. The presence of an RC slab increased the plateau impact force by approximately 15% and reduced the maximum displacement by about 13%, indicating a significant enhancement in joint stiffness and deformation resistance. A higher impact velocity led to larger impact force and displacement response due to stronger inertia and strain-rate effects. Under the same total impact energy, three consecutive low-velocity impacts resulted in substantially lower displacement and lower sustained impact force than a single high-velocity impact. In addition, a simplified analytical method of predicting displacement response was proposed by employing an equivalent SDOF model, and it gave an accurate prediction within 15% error as compared to testing results.