Experimental study on concrete spalling in prestressed slabs subjected to fire

Experiments on the fire resistance of 15 prestressed concrete (PC) simply-supported slabs and 9 two-span unbonded PC continuous slabs were conducted. Preliminary conclusions drawn are that concrete spalls more easily or more seriously when the compressive stress is higher or the tensile stress is lower on the surface exposed to fire, and when the strength and water content of concrete at ambient temperature are higher. Based on the test results, an expression for the top envelope surface of the concrete spalling is presented by taking the average standard concrete cube strength at ambient temperature as the x-axis, the concrete water content at ambient temperature as the y-axis, and the normal stress level of concrete extreme fiber in the pre-compression zone of a slab at elevated temperature as the z-axis. To facilitate design and application, an expression for the top envelope surface of the concrete spalling is presented by keeping the x-axis and the y-axis the same, and the normal stress level of concrete extreme fiber in the pre-compression zone of a slab at ambient temperature as the z-axis.