Experimental study on the fire behaviour of reinforced concrete slabs under combined uni-axial in-plane and out-of-plane loads

In this paper four large scale fire tests on the reinforced concrete slabs, under combined uni-axial in-plane and out-of-plane loading conditions with vertical restraint at four corners of the slabs, are presented. The research focuses on the quantitative relationship between horizontal restrained force and deformations, cracking patterns and spalling of the slabs in fire. Also the vertical restraint forces at the four corners of the slabs were measured in the tests. Comparisons of the results indicate that the compressive uni-axial in-plane loads have a considerable effect on the number and directions of cracks on the top of the concrete slabs in fire. The uni-axial in-plane restrained slabs have larger mid-span deflections and lower deflection recovery ratios than the slabs without in-plane loading. In addition, the test results indicate that increasing reinforcement ratio can effectively prevent the integrity failure of the restrained slabs. The research generates valuable test data which can be used to validate the numerical models developed by fellow researchers in the field of structural fire engineering.