Experimental Study On Shear Behavior Of Reinforced Concrete Beams

In this paper,the bearing capacity of reinforced concrete simply supported beam under indirect loading mode under thermal coupling and fire action is studied.Through experiment study,observation and analysis of the indirect load under the action of a coupled thermo-mechanical model of reinforced concrete beam inclined section destructive state and strength degradation law,as well as the high temperature effect of reinforced concrete beam after fire in the inclined section of the indirect load mode crack law of development,destructive state and the residual bearing capacity for inclined section.The finite element software is used to model the test beam,and the numerical simulation analysis is carried out.The main research results are as follows:(1)the test results show that the failure of the test beam is caused by the shear failure of the main oblique crack near the junction of the main and secondary beams under the thermal coupling effect.Therefore,the additional reinforcement at the junction of secondary beam and main beam is of great significance for improving the fire-resistant bearing capacity of reinforced concrete beams under indirect loading mode.(2)the test results showed that the specimens with additional reinforcement,namely the specimens designed according to the "strong shear and weak bending",were subjected to obvious bending failure under the action of thermal coupling.There is no obvious failure at the junction of the secondary beam and the main beam.Therefore,the failure forms of specimens designed according to the current code of "strong shear weak bending" under thermal coupling are in line with the design expectation of "strong shear weak bending".(3)the effect on the fire after the specimen under static loading,the results showed that the specimens without additional reinforcement,namely the specimen is designed according to the "strong bending the weak cut",as the second beam and girder junction inclined section cracks caused by shear failure,therefore,subjected to fire after the destruction of the specimen and normal temperature contrast specimen form are basically the same,no obvious changes,but after thermal coupling shear bearing capacity of the specimens under no load when subjected to fire the shear bearing capacity of the specimen.(4)static loading was carried out on the specimens subjected to fire.The test results showed that the specimens with additional reinforcement,namely the specimens designed according to "strong shear and weak bending",were all subjected to bending failure.Therefore,the failure forms of the specimens subjected to fire and the normal temperature comparison specimens were basically the same.However,the ultimate bearing capacity of the specimens subjected to fire was significantly lower than that of the specimens subjected to room temperature contrast.The ultimate bearing capacity of the specimens subjected to non-thermal coupling effect was approximately 14.2% lower than that of the specimens subjected to room temperature contrast,and the ultimate bearing capacity of the specimens subjected to thermal coupling effect was approximately 19.1% lower than that of the specimens subjected to room temperature contrast.(5)it can be seen from the load-deflection curve of the measured specimen that: in the static load test process of the specimen under the action of fire,the deflection change of the specimen under shear failure is not obvious,and the beam under shear failure is sudden and has obvious brittle failure characteristics;Flexural failure specimen deflection deformation is large,showing the characteristics of ductile failure.Due to the deterioration of reinforced steel and concrete materials,the stiffness ratio of the test beam decreases to some extent.(6)it can be seen from the load-strain curve of the measured specimens that the specimens subjected to the action of fire are subjected to the same load,and the strain of the measured concrete,longitudinal reinforcement and stirrup is generally greater than that of the tested specimens at room temperature.