Research On The Shearing Resistance Performance Of Reinforced Concrete Simply Supported Beam After Fire

Fire is one of the more frequent disasters today.Studies have shown that the high temperature of fire will severely reduce the performance of reinforced concrete structural materials.Therefore,the high temperature of building fires will seriously threaten the bearing performance of reinforced concrete structures.It is an important practice to study how to further improve the bearing performance of reinforced concrete structures after fire.Value and theoretical significance.In this paper,the load-bearing performance of reinforced concrete simply-supported beams is taken as the object of study.With the aid of a large-scale fire simulation test system,the high-temperature effects of fire on reinforced concrete simply supported beams are first simulated,and then the sample of reinforced concrete simply supported beams subjected to fire is then tested.The remaining oblique load bearing capacity loading test was performed to observe and analyze the appearance of the test beam after fire exposure,the cracking process of the post-fire loading test,deflection deformation process,failure characteristics,and residual bearing capacity.A large finite element analysis software was used to simulate the test beam.The main results of this study are as follows:(1)From the loading of the test piece after the action of the fire to the development of the crack in the test of failure,the corresponding load value of the diagonal crack of the test piece after the fire is lower than the corresponding load value of the oblique crack of the normal temperature comparative test piece.Under the same temperature rising condition,the larger the shear span ratio,the smaller the ratio of longitudinal reinforcement ratio and the ratio of stirrups,the lower the corresponding load value when oblique cracks occur.The failure pattern of the 12 specimens was the same.With the development of the main oblique cracks,the concrete in the shear zone eventually broke down and the specimen lost its bearing capacity.(2)From the point of view of the ultimate bearing capacity of the test piece,when the other conditions are the same,the ultimate bearing capacity of the specimen subjected to high temperature fire is lower than the ultimate bearing capacity of the normal temperature comparative specimen,and at the same temperature increasing condition,the shear ratio is greater.Large,the lower the ultimate bearing capacity,the greater the reinforcement ratio of stirrups,the greater the ultimate bearing capacity,the greater the reinforcement ratio of longitudinal reinforcement,the greater the ultimate bearing capacity.(3)From the load-displacement curve of the actual test piece,under the same shear-span ratio,the vertical load of the same size is loaded,and the vertical displacement of the test piece after the high temperature effect of the fire is greater than the vertical displacement of the normal temperature contrast sample,indicating that the fire has experienced The stiffness of the specimen decreases after high temperature,and the deflection maximum value of the test specimen is higher than that of the normal temperature contrast specimen.The test results show that under the same temperature conditions,the larger the shear ratio,the greater the midspan deflection,the greater the stirrup ratio,and the greater the midspan deflection.(4)The test results show that,during the fire loading process,the test specimens subjected to the load increase in the static load test after the fire,and the ultimate bearing capacity is smaller than that of the specimens that were not loaded during the heating process.(5)From the load-concrete strain curve of the actual test piece,the larger the shear span ratio of the test piece after the high temperature effect of the fire,the greater the concrete strain in the mid-span tensile zone.From the load-reinforced strain curve of the test piece,the larger the shear span ratio of the test piece subjected to the same temperature condition,the greater the bottom longitudinal bar strain at the mid-span position.For the measured hoop strain,before the main oblique cracks are generated,the strain of the stirrups is changed little before the normal temperature contrast specimens are formed.After the high temperature effect of the fire,the specimens undergo fine cracks due to the high temperature effect.Before the main oblique cracks are generated,the stirrups are generated.The strain is much larger than the normal temperature contrast specimen.(6)With the use of finite element analysis software,the distribution of the temperature field of the test piece and the static load bearing performance after the fire were simulated.The analysis results are in good agreement with the test results.