Effect of joint details on progressive collapse resistance of precast concrete structures

Recently, precast concrete (PC) structures are vulnerable to progressive collapse, because during construction, the structural integrity of the beam-column joint is poor. Even after construction, the interface between PC beam and column is a critical section, due to the discontinuity of concrete and reinforcement. In this study, to investigate the progressive collapse resistance of PC structures with various joint details, three moment sub-frames were tested under monotonic vertical loading. Addressing the actual joint details used in industrial PC buildings, such as warehouses and factories, prestressing was applied to the PC beam, and wet connection was used for beam-column joints. As a test parameter, the joint details were compared (i.e., monolithic reinforced concrete (RC) joint, PC with pinned joint, and PC with continuous joint). The test results showed that the PC specimen with continuous joint exhibited structural behavior equiv-alent to the RC specimen in terms of failure modes, peak strength, deformation, lateral support reaction, and strain. However, the PC specimen with pinned joint showed significantly less strength than that of the PC specimen with continuous joint, due to the discontinuous top and bottom rebars in the beam-column joint. Further, the deformation and failure modes of PC specimens with pinned joint differed from those of the other specimens (i.e., rigid rotation of PC beams without flexural yielding, and concrete breakout around dowel bar). Using a finite element (FE) model, a parametric study was conducted. According to the analysis results, the progressive collapse resistance was significantly affected by the continuous rebars of the PC beam in the beam-column joint. Based on the test and analysis results, the maximum allowable uniformly distributed floor loads sustained by PC system was estimated. Further, design recommendations to improve the progressive collapse resistance were discussed, such as use of continuous top bars, strength limitation of dower bars, and effect of prestressing force.