Progressive Collapse Resistance of Posttensioned Concrete Beam-Column Subassemblages with Unbonded Posttensioning Strands

Abstract

In this study, the behavior of posttensioned reinforced concrete (PC) beam-column subassemblages subjected to the loss of a middle column is investigated experimentally. The influence of unbonded posttensioning strands (UPS) with a parabolic curve on the behavior of reinforced concrete (RC) frames to resist progressive collapse is also quantified. Test results indicated that UPS have little effect on the yield load and first peak load of frames to resist progressive collapse. However, UPS could significantly increase the ultimate load capacity of the frames because stretching of strands could provide considerable additional vertical load resistance. UPS will aggregate the damage in the beam ends near to the middle column, although they may relieve the damage in the beam ends near to the side column. Moreover, UPS may change the load-resisting mechanism of the RC frame. No reliable compressive arch action developed in PC beams to resist progressive collapse because the UPS changed the distribution of the compressive stress along the beams. In addition, the effects of span/depth ratio and effective prestress in UPS on the progressive collapse resistance of PC frames are investigated. It is found that the span-depth ratio has a significant effect on the performance of RC frames to resist progressive collapse, but not the PC frames. The effective prestress in UPS has little effects on the yield load and initial stiffness of the PC frame, but it may significantly affect the ultimate deformation capacity and ultimate load capacity of the PC frame.