Influence of Various Initial Side-Column Damages on the Horizontal and Vertical Mixed Progressive Collapse Behavior of RC Planar Frames

Blast loads not only cause the single key column failure of reinforced concrete planar frames, but also simultaneously introduce damage to other adjacent members. By conducting quasi-static test on a 1:3 scaled-down specimen of a RC planar frame under the middle column removal scenario, this paper investigated the influence of side-column initial damages on the horizontal and vertical mixed progressive collapse behaviors of RC planar frames. Before pouring concrete, polyurethane foam was filled into the form of the specimen, and rebars were uniformly polished to equivalently prefabricate the blast-induced initial damage of side columns. In order to overcome the adverse effects of asymmetric deformation and failure of side columns on the loading of specimens, a lying loading platform was built using multilayer steel supports. The validated finite-element models were used to perform supplemental calculations for more damage conditions of the side columns on the basis of experimental results. The results showed that when the initial damage degree of the side column does not exceed 58%, the collapse resistance curves of RC planar frames include three complete action stages, and the failure position of RC planar frame transfers from the beam adjacent to the middle joint to the side columns. When the initial damage degree of the side column reaches 78%, the RC planar frame completely fails before the collapse resistance in the compressive arch action stage reaches its peak. The final failure of RC planar frames is controlled by side columns, which means that RC planar frames are subjected to a horizontal and vertical mixed progressive collapse.