Residual load-bearing capacity of large-scale prestressed concrete roof slabs after fire exposure

Abstract

Large-scale prestressed concrete (PC) roof-slabs are fundamental structural components extensively used in industrial construction. These slabs have large spans and thin profiles, rendering them susceptible to substantial degradation in load-bearing capacity when exposed to high-temperature fires. Currently, there is a lack of experimental research data on the performance deterioration of such large-scale slabs under high-temperature fire conditions. This highlights the significance of conducting experimental investigations into the fire resistance properties of large-scale PC slabs from theoretical and practical perspectives. In this study, 11 large-scale PC slab specimens were manufactured, with three slabs designated as reference specimens for comparison at ambient temperature. Leveraging a large-scale fire simulation test system, the remaining eight PC slabs were subjected to post-fire residual load-bearing performance tests, considering variations in fire exposure duration and cooling methods. The temperature field distribution during the heating and cooling processes, the deflection deformation characteristics, and the crack distribution patterns after cooling of the PC slabs were observed and analyzed. Furthermore, a comparative analysis was conducted to assess the impact of different fire exposure durations and cooling methods on the degradation of the overall load-bearing performance of slabs. Post-fire static loading tests showed that the slabs retained good overall load-bearing performance after fire exposure. The slabs exhibited the structural characteristics of integrated slab and rib behavior, with the primary rib remaining the key load-bearing component. The overall load-bearing capacity of the slabs after a fire primarily depends on the residual load-bearing capacity of the primary and secondary ribs. Compared to slabs under ambient conditions, the overall flexural stiffness and ultimate load-bearing capacity of the fire-exposed slabs showed varying degrees of reduction. The slabs subjected to natural cooling after different fire exposure durations (30, 45, 60 and 75 min) experienced reductions in ultimate load-bearing capacity by 1.5, 2.3, 4.4, and 15 %, respectively, compared to ambient-condition slabs. For slabs cooled with water, the reductions were 2.8, 6.0, 7.4, and 12.4 %, respectively. The flexural stiffness of slabs cooled naturally after fire exposure was lower than that of slabs cooled with water. The experimental results indicated that large-scale PC slabs exposed to fire for equivalent standard heating times of 24, 39, and 50 min experienced less than 8 % reduction in overall post-fire load-bearing capacity. Therefore, from a load-bearing capacity perspective, large-scale slabs of this type exposed to standard heating for up to 50 min still maintain good load-bearing performance. The findings of this study provide valuable reference data for fire-resistant design, post-fire assessment, and reinforcement of large-scale PC slabs.