PROGRESSIVE COLLAPSE PERFORMANCE OF PRESTRESSED CONCRETE FRAMES UNDER PENULTIMATE COLUMN REMOVAL SCENARIO

Considering that the direction of bending moment at the beam end nearby the removed column will reverse, which may disagree with the profile of prestressing strands. Thus, the prestressed concrete frame may have high vulnerability for progressive collapse. In this study, experimental and numerical studies were performed to study the performance of unbonded prestressed concrete (PC) beam-column sub-assemblies subjected to a penultimate column removal scenario to resist progressive collapse. Two half-scale PC beam-column sub-assemblies with different strand profiles were tested by Pushdown loading procedure. Failure modes, the involution of load resisting mechanisms, and ultimate load resistance were analyzed. To quantify the effect of the strand, a non-prestressed reinforced concrete beam-column sub-assembly was designed, the geometrical dimension and reinforcement ratio of which were consistent with the PC beam-column sub-assemblies. It is found that the presence of the strand leads to a greater load resistance, lower deformation capacity and different failure modes. The considerable tension in the strand cause significant second-order effects in the side column, leading to large eccentric compression failure. To further study the performance of PC frames against their progressive collapse, high-fidelity numerical models built by LS-DYNA were used to conduct a series of parameter studies. It is found that prestress forces can increase compressive an arch action. The strand can significantly enhance the ultimate load resistance at a large deformation stage.