Experimental Study On Shear Bearing Capacity Of Reinforced Concrete Simple Supported Beams Without Web Bar Under Fire

Fire is one of the most frequently occurring disasters.The high temperature of the fire will seriously reduce the performance of reinforced concrete structure material and threaten the bearing safety of reinforced concrete structure.It is of great theoretical and practical significance to study the bearing performance of reinforced concrete structures subjected to fire and high temperature.In this paper,the bearing capacity of diagonal section with simple supported beams is studied.With the aid of large scale fire simulation test system,the test of fire heating and constant load coupling of full scale reinforced concrete simple supported beams is carried out.The design of the test beam takes into account the shear span ratio,the load ratio of the thermal mechanical coupling,and the reinforcement ratio of longitudinal reinforcement.Based on the test,the distribution law of temperature field,deflection,fire resistance rating and failure characteristics of the test beam during heating and cooling are observed and analyzed.ABAQUS large scale finite element analysis software is used to simulate and analyze the test beam.The main research results are as follows:(1)The test results show that the internal temperature of the specimen is related to the distance from the fire surface,and the closer the distance to the fire is,the higher the temperature is.During the initial stage of heating,the temperature gradient inside the test points showed obvious temperature gradient,indicating that the concrete had certain thermal inertia.(2)The test results show that the load ratio of simple beam without web bar has little influence on the temperature change law of the test beam,and the shear span ratio has noeffect on the temperature change law of the simple supported beam without web bar.(3)The test results show that the greater the load ratio of the specimen is,the faster the deformation will be under fire.When the load ratio is more than 0.5,the load has greater influence on the deflection deformation of the simply supported beam without the web bar under the thermal coupling effect,and the fire resistance of the specimen obviously declines.(4)It can be seen from the measured deflection curve that the deformation of the reinforced concrete simple beam without web bar will increase suddenly when the thermal coupling effect is close to the fire resistance rating,and the phenomenon of obvious diagonal section shear failure is more abrupt.(5)The test results show that the shear failure of the reinforced concrete simple supported beam without web bar is less than the normal temperature limit load,that is,the effect of high temperature will obviously affect the shear capacity of the reinforced concrete simple beam.(6)The test results show that the shear span ratio has great influence on the fire resistance of beams without web bar.The larger the shear span ratio,the shorter the fire resistance.When the shear span ratio exceeds 3,the degree of fire resistance rating decreases more obviously.(7)The test results show that the reinforcement ratio of the longitudinal reinforcement is an important factor affecting the fire resistance rating of the simple supported beam,the smaller the reinforcement ratio of the longitudinal reinforcement,the shorter the fire resistance rating of the simple supported beam,the lower the shear ability of the specimen under the action of the thermo mechanical coupling.(8)The ABAQUS finite element simulation software is used to analyze the displacement of the specimen under the effect of temperature field and thermal coupling,and the results are compared with the experimental results,and the agreement is good.