Performance of Unbonded Local Prestressed Concrete Beam–Column Substructures against Progressive Collapse

In large public buildings, a combination of long-span prestressed concrete beams and short-span reinforced concrete beams is often employed due to functional requirements. These structures are designated as local prestressed concrete (LPC) structures. However, there is still a lack of research into the progressive collapse of LPC structures. Consequently, in this paper, the progressive collapse performances of unbonded local prestressed concrete (UBLPC), bonded local prestressed concrete (BLPC), and unequal-span reinforced concrete (USRC) substructures were tested under middle column failure. The results suggest that the progressive collapse of LPC substructures could be divided into two stages: the beam–beam stage and beam–link stage. The main crack in the long-span beam appeared at the junction of the reinforced and nonreinforced regions of the longitudinal reinforcement. The fracture of the top rebar of the short-span beam resulted in a complete loss of flexural capacity, which signaled the structure’s transition into the beam–link stage. Theoretical analyses were conducted to reveal the effects of bond on crack development and progressive collapse resistance. The findings indicated that the collapse resistance of UBLPC substructures was inferior to that of BLPC substructures. However, the allowable deformation of unbonded prestressed tendons was more substantial. Moreover, this paper presented an efficient numerical modeling method to simulate the progressive collapse behavior of UBLPC substructures with reasonable accuracy.