Experimental Research On Fire Resistance Of A-type Joints In The Reinforced Concrete Structure With Bearing Column Girder Transfer Floor

Bearing column girder transfer floor is a common structure in construction,so the research of the bearing behavior and deterioration law under fire has great theoretic and realistic significance.Aiming at A-type joints in the reinforced concrete structure with bearing column girder transfer floor,we carry out fire resistance experiment which the joins are exposed to fire and coupling with vertical loads.In the experiment,we make the joists expose three or fore sides in fire.Based on the experimental phenomenon,temperature field distribution,deformation feature and failure mode of the specimens are analyzed and summarized.And finite element simulation with ABAQUS is used to compare with the test results.The main test and analysis results are as follows:(1)The results show that the measured temperature of the core section of the bearing column girder transfer floor joint is lower than that of the other section under the fire condition,and the temperature inside the core area is influenced by the "encirclement" of the surrounding joists and the brackets.(2)It is found that the cracking of the specimen joists is mainly the curved vertical cracks in the bottom tension zone,and the vertical cracks begin to reach the column direction extends obliquely when the cracks went to the center of the section of the joists when the temperature is reached.The failure of the specimen is caused by the development of several bending main cracks.First,it is carried out at the relatively large part of the bending moment of the joist,and then at a certain distance from the brace,some cracks are developed.In the shear force under the action of the cracks in the direction of the column to extend to main cracks.(3)The test results show that the vertical deflection of the A joist of thebearing column girder transfer floor(TZHA)is relatively symmetrical about the brackets,and the cracks are also in the two side evenly distributed.The cracks in the girder are basically distributed in the range of 400mm-1000 mm from the midpoint of the span of the joist,and the main cracking cracks,the serious parts of the concrete falling off and the fracture parts of the steel are concentrated at about 600 mm from the midpoint of the span.(4)The test results show that the main cracks in the bottom of the specimen girder are wide and the bending deformation is concentrated,and the shape of the section of the joist is broken and no obvious shear damage is observed.(5)The test results show that the greater the load ratio applied to the specimen under the thermo-mechanical coupling,the shorter the refractory time,that is,the refractory limit is smaller.Under the same conditions of other parameters,the load ratio of 0.4 of the specimen,the fire resistance and more concentrated in about 140 min.Load ratio of 0.6 of the specimen,the fire resistance is significantly shorter.(6)Test phenomenon shows that the specimen reaches the fire limit and the deformation and cracking of the joists are obvious,the continuous heating and load coupling will exacerbate the deformation of the specimen,the concrete fall off lead to the steel gradually exposed and may lead to the phenomenon of longitudinal reinforcement,tirrup got high temperature rupture.Therefore,in the actual fire,the beam longitudinal reinforcement of the beam structure will cause the tray to lose support,result in the collapse of the upper structure,result in serious consequences.The conversion structure of the fire resistance must be highly valued.