Mechanical Properties Of Fire Burnt Concrete Beam

The safety of a fire burned building is weakened because its material and structural performance are seriously deteriorated.The physical and mechanical properties of the reinforced concrete beams in the building also decrease.In this thesis,the overfire effects to the performance of reinforced concrete beams are studied.The relevant results can be used as reference for the conduction of concrete strength test,the structural member strength analysis,and the structural safety evaluation of a fire burned building.A series of experiments on the performance of fire burned reinforced concrete cubes and reinforced concrete beams are carried out,taking into consideration such factors as concrete strength grade,steel bar diameter,burning temperature,and burning time.Numerical simulations are then conducted for further analyses.The main contents and conclusions are as follows.(1)In the high temperature furnace,the reinforced concrete cubes were subjected to different burning temperatures and burning times,and then their compressive strength were tested.The cubes are divided into three groups according to their concrete strength grade.According to the test results,the relation curve between the concrete strength and the burning temperature and burning time were drawn respectively.The experimental results show that the compressive strength of concrete decreases with the increase of burning temperature.When the burning time is rather long,and the burning temperature is between 500? and 700?,the compressive strength decreases the maximum.In addition,the apparent color of the concrete,the degree of spalling and the bond with the steel bar after different burning temperature and burning time were recorded.(2)The tensile test of steel bars in the burned reinforced concrete cubes were carried out.The curves of the yield strength,tensile strength and elongation rate versus the burning temperature and time were drawn for steel bars with diameters of 18,20,and 25 mm respectively.According to the test results,When the burning temperature does not exceed 500? and the burning time does not exceed 60 minutes,neither the yield nor the tensile strength changed obviously.When the burning temperature is between 500? and 700?,with increasing burning time,both the yield and the tensile strengths of the steel bar decreased slightly with the increase of burning time.When the temperature is between 700? and 900?,with the increase of the burning time,the yield strength decreased linearly with the temperature,while the tensile strength did notsignificantly change.(3)Four reinforced concrete beam were made.The fire burning test were carried out for three beams subjected to lateral loads.The results were compared with those of the beam not going through a fire burning.The load-displacement curves were obtained for comparison analysis.The results show that the fire burned beam has no inflection point when the tension zone concrete is cracked.(4)The finite element model of reinforced concrete beam was established,and the numerical analyses were conducted with the test data.The numerical simulation results are in good agreement with the test results,which verifies the correctness of the model.The finite element models of 3-,4-,and 5-metre span concrete beams were created and analyzed.According to the results of the simulation analyses,the load-displacement curves of different span beams with different fire conditions were plotted.Simulation analyses show that with the same burning time and burning temperature,the beam with greater span suffered more serious bending performance deterioration.