Progressive Collapse Response of Reinforced Concrete Assembly with Realistic Boundary Conditions

Previous studies on reinforced concrete (RC) beam-column subas-semblies under a column removal scenario are helpful to under -stand the load-resisting mechanisms of RC structures against progressive collapse, but most of these studies failed to simulate actual boundary conditions, which were simplified as fixed bound-aries to allow sufficient development of the load-resisting mecha-nisms. These studies were unable to reflect the response of joints and side columns under progressive collapse. To fill this gap, an experimental program on six half-scale beam-column subassem-blies with joints and side columns was designed and tested to fully understand the effects of boundary conditions on the structural behavior of RC planar frames against progressive collapse. Three subassemblies were specially designed, while the other three were ordinarily designed to quantify the benefits of special detailing. The test results show that the effects of boundary conditions on the development of load-resisting mechanisms are marginal, whereas the effects of special detailing are significant. Specifically, speci-mens under a middle-column removal scenario and a penultimate-column removal scenario develop similar compressive arch action (CAA) capacities and catenary action (CA) capacities. The CAA capacity dominates the load resistance of specimens with ordinary detailing. In contrast, the CA capacity governs the load resistance of specimens with special detailing mainly due to the larger areas of longitudinal reinforcing bars and the greater rotation capaci-ties of beam ends. However, boundary conditions can greatly affect the failure mode of specimens with ordinary detailing. Finally, an analytical study was performed to demonstrate the contributions of axial force and shear force to load resistance. According to test results and analytical analyses, RC frames with special detailing have sufficient rotational capacity to develop adequate tie forces to resist progressive collapse.