Study On The Effect Of Mortar Cover On Mechanical Behaviour Of RC Structures After Fire

In order to investigate the effect of mortar cover on the mechanical behavior of reinforced concrete(RC) structures, the following studies are carried out: (1) Infrared thermal image testing technology(IRT) is used to detect the average temperature rising of the infrared thermal images from twelve fire-damaged concrete cubes without mortar cover and fifteen fire-damaged concrete cubes with mortar cover, and the compressive strength testing is also conducted to all these concrete cubes; (2) The thermal property of mortar cover is assumed based on the property of existing materials. Using the thermal-structure coupling function of ANSYS, the compressive strength of both concrete cubes with and without mortar cover after subjected to fire are simulated; (3) Using the thermal-structure coupling function of ANSYS, the temperature field of RC columns with and without mortar cover under four surfaces heated and the seismic behavior after heated are analyzed, and the effect of mortar cover on the temperature field and seismic behavior is discussed. Based on test and simulation results, the conclusions are as follows:(1) The failure patterns derived from the compressive strength test change from pyramid failure at ambient temperature to integral failure after subjected to high temperature. Compared with the failure patterns of concrete cubes with mortar cover, the failure patterns of concrete cubes without mortar cover are more close to integral failure.(2) The average temperature rising of infrared thermal images of specimens with mortar cover is less than that of specimens without mortar cover. Besides, specimens with mortar cover have a higher residual compressive strength than that of specimens without mortar cover. The mortar cover could effectively mitigate the fire damage of concrete structures.(3) Based on the test results, four regressive equations for evaluating the highest subjected temperature of concrete and its compressive strength reduction index are proposed.(4) Based on the simulation results, the thermal properties of mortar cover taking into account the influence of the gap between concrete and mortar cover can be used to calculate the temperature field of RC structures with mortar cover, and the temperature field of a concrete cube under four surfaces heated is annularly distributed and the temperatures decline from surface to the center.(5) The mortar cover could effectively mitigate the fire damage of concrete columns on the temperature, improve the strength and reduce the stiffness degradation.