Small-Scale Tests on Tensile Membrane Action of Reinforced Mortar Slabs at Elevated Temperature

Abstract

In case of fire, reinforced concrete floor slabs are heated on the lower surface and are deflected due to the temperature gradient along the thickness direction and the reduction in strength at elevated temperature. In accordance with the deflection of the floor slab, the membrane stress developed and caused the enhancement of load-bearing capacity. This paper discussed, in the basis of the results of high-temperature loading tests of small-scale reinforced mortal slabs, the amount of deflection due to the temperature gradient and the influence of the bottom reinforcement temperature on the maximum strength, and the enhancement factor. The parameters include the support conditions and the steel temperature at the bottom reinforcement. The thermal deflection of the two-way slab due to the temperature gradient approximately agreed with the theoretical value of the one-way slab. The maximum load-bearing capacity in case of the bottom reinforcement temperature of 400 °C was equal to or larger than that at room temperature. The decrease in the maximum strength above 500 °C was lower for the two-way slabs than for the one-way slabs. The enhancement of the maximum strength due to tensile membrane action was confirmed from the test result without punching shear failure.