Experimental Research On Mechanical Behaviors Of Reinforced Concrete Columns With Sustained Axial Load After Exposure To Fire Or High Temperatures

There are relatively little researches on mechanical behaviors of fire-damaged reinforced concrete (RC) found by far. Moreover, the tested specimens were not loaded during the fire or high temperature exposure because of facility constraint. Therefore, the effect of the double action of loading and high temperature exposure on the mechanical behaviors of RC structure was not considered. In the paper the mechanical behaviors of square RC stub columns with sustained axial load afer the entire period of high temperature exposure and the hysteretic behavior of full-scale circular RC columns with sustained axial load after the entire period of fire exposure were experimentally investigated. It can be expected to make a rational fire-damage assessment of RC structures after exposure to fire by considering the effect of sustained axial load and the entire period of fire or high temperature exposure. The experimental researches also be used as a basis for make a rational repair policy. The main works are summarized as follows:(1) Tests on temperature distributions of four RC specimens, including two square RC stub columns heated by an electric furnace and two full-scale circular RC columns heated by a hybrid heating method, were carried out to experimentally study the characteristics of temperature field of RC members during the fire exposure and cooling phase. The test results were also used to verify the finite element model of thermal analysis.(2) Based on the art of literature of the researches on thermal properties of steel bar and concrete at elevated temperature conducted by the researchers at home and overseas, a finite element model and mechanical behavior model of fire or high temperature were developed to simulate the temperature fields of RC columns which were carried out by the author and other researchers. The FE modeling were verified by the numerical results which are in good agreement with the tested results.(3) Experimental study on the axial mechanical behaviors of 13 square RC stub columns, including two specimens at room temperature and eleven specimens after the entire period of high temperature exposure and cooling phase, was carried out. The effect of high temperature and the axial load ratio on residual strength, axial stiffness and residual deformation of RC stub columns after exposure to high temperatures were experimentally studied.(4) Experimental study on the hysteretic behavior of 5 full-scale RC columns, including one specimen at room temperature and four specimens after exposure to the entire period of fire exposure and cooling phase, were carried out. The effect of fire duration time and the axial load ratio on the residual load-bearing capacity, flexural rigidity, ductility and dissipated energy of the fire-damaged RC columns were experimentally studied.