Fire and post-fire performance of unbonded semi-precast prestressed reinforced concrete beams

The integration of semi-precast concrete beam preparation methods with prestressing structural measures aims to achieve superior mechanical properties while complying with green construction principles. However, the damage mechanism of semi-precast prestressed concrete beams (SP-PCBs) under fire conditions is not clear. In this study, the cross-section temperature distribution, prestressing loss pattern, and residual load-carrying capacity of the SP-PCBs were investigated by conducting standard fire tests. The results show that increasing the thickness of the protective layer of prestressing bars can delay the time of damage by high temperature and thus increase the fire resistance limit of the SP-PCBs. Higher prestressing levels and rebar ratios contribute to the cracking resistance of the SP-PCBs, although the stress loss is obvious. After the fire, the distinct SP-PCBs showed different degrees of reduction in load-carrying capacity and stiffness, but still exhibited excellent fire resistance and avoided brittle damage. Increasing the reinforcing ratio increases the residual load-carrying capacity of the SP-PCBs, while increasing the prestressing level has a relatively small effect. Increasing the height of the post-cast layer slightly reduces the stiffness and ductility of the SP-PCBs, but does not significantly affect the load-bearing capacity. In addition, this paper establishes a theoretical calculation model for the residual load-bearing capacity of the SP-PCBs after the fire, and verifies the accuracy of the model by experimental results, which provides a practical theoretical basis and reference for the design and evaluation of the fire resistance performance of the SP-PCBs.