Analysis and evaluation on residual impact resistance of CFST composite frames under column removal scenario

To investigate and evaluate the dynamic response and residual impact resistance of CFST (concrete-filled steel tubular) composite frames after the failure of vertical load-resisting components, two 1/4-scaled two-storey and two-span CFST composite subframes under the penultimate column and corner column failure conditions were tested in three consecutive impacts. The tests results show that the substructures under the penultimate column and corner column failure conditions after being statically loaded to 360 mm can both resist the three consecutive impacts. The aggravation of the cracks of the steel beams and the crush of the concrete slabs at the connections area were observed after the impacts. As the impact energy of three impacts increases, the average impact force of both two specimens increases and the substructure with penultimate column failure shows better anti-impact capacity than the specimen with corner column failure. The finite element model analysis shows that the damage and energy consumption of the structures under impact loading primarily concentrate on the failed span and the impacted storey, where the ring plate connections are the most dominant energy-consuming components. Over 75 % of the impact resistance is provided by the flexural action of the composite beams. After being statically loaded to 360 mm, the structures can still resist the impacts which equal to 20.7 % and 18.5 % of the mass of the upper slab in the structures with the penultimate column and corner column failure, respectively. Additionally, a simplified prediction method is proposed for the residual anti-impact energy-consuming capacity of the substructures with column failure which is found to be negatively linearly related to the initial vertical displacement.