Experimental and numerical investigation on progressive collapse resistance of reinforced concrete beam column sub-assemblages

Based on alternate load path approach, an experimental program was conducted for investigating progressive collapse resistance of reinforced concrete (RC) beam-column sub-assemblages under a middle column removal scenario. Two one-half scaled sub-assemblages were designed with seismic and non-seismic detailing to check the effect of detailing on structural behavior. During the tests, with increasing deformation of the specimens, different structural mechanisms developed subsequently, i.e. flexural action, compressive arch action (CAA) and catenary action. Compared with conventional yielding strength (i.e. capacity of flexural action without considering the existence of beam axial forces), both CAA and catenary action can significantly enhance the structural resistance. The understandings towards these two mechanisms were illustrated at structural, sectional and fiber levels. To simulate the structural responses of the specimens with severe geometric and material nonlinearity, a component-based joint model was proposed and incorporated into macromodel-based finite element analysis in which beams were modeled with fiber elements. The joint model consisted of a series of springs to characterize bond-slip behavior under large tension. Numerical results agreed well with test results. Then the numerical model was used to conduct some parametric studies on the boundary conditions of test specimens, including the axial and the rotational restraints.