Experimental investigation on dynamic response behavior of PC beam-column sub-assemblages under middle-joint drop-weight loading

The dynamic response of frame structure in progressive collapse has been investigated by some scholars by removing the column suddenly. However, the research cannot exhibit the effect of blast load on the dynamic response of the structure. Especially in a close-field explosion, a large axial tension force may occur in the cross-section of the column suffered from the blast load directly. It is the main factor causing dynamic response and subsequently leading to progressive collapse. This paper experimentally studied the dynamic response behavior of prestressed precast concrete sub-assemblage (PCS) through middle-joint drop-weight loading, and the tension force caused by the failed column was applied downward on the top of the middle joint of subassemblage through drop hammer impact. The same loading condition was also applied to the reinforced concrete sub-assemblage (RCS) to compare the dynamic response behavior. The results showed that all the sub-assemblages exhibited flexural damage mode. Compared with RCS, more serious damage occurred concentratedly at the beam-column interface in PCS, but no prompt damage appeared in the beams. The sub-assemblage went through local dynamic response and global dynamic response stages in succession. Reverse arch action (RAA) emerged during the local response stage due to the pronounced inertial action at the middle joint, and it became more significant with increasing impact velocity. Compared with RCS, the pretension of steel strands may enhance the effect of RAA in PCS. Compressive arch action (CAA) emerged during the global response stage with the energy transferring from the kinetic energy to strain energy when middle joint displacement (MJD) increased continuously. With increase of impact velocity, the contribution of steel strands tension in resisting collapse increased significantly. The damage mode of the beam end in PCS at the peak MJD was almost the same as that under quasi-static loading at the same MJD, and the strain energy was also approximately identical to that under quasi-static loading. Based on the premise of flexural damage mode of PCS, the peak MJD can be determined according to the vertical resistance of PCS under pushdown loading using the work-energy principle.