Experimental Study On Shear Behavior Of Reinforced Concrete Continuous Beams Subjected To Fire

According to the relevant investigation and research found that the current construction projects,most of the application of reinforced concrete structure.Under the influence of high temperature,the mechanical properties of steel and concrete materials will be greatly weakened,leading to serious internal force problems,the structure bearing capacity will be seriously reduced,more and more will affect the safety of the structure,so now more and more attention is paid to the fire resistance of reinforced concrete in structural engineering and disaster prevention and control.Article use big fire simulation test system,of reinforced concrete continuous beam cross section bearing quality carried out the study,first the fire simulation on the high temperature impact of reinforced concrete,the second after affected by the fire of the reinforced concrete continuous beam specimens for inclined section bearing load performance test,then after affected by the fire of the test beam outside like split,the process,the condition of remaining bearing capacity and deformation of immunity,etc.In the experiment,a total of 5 full-length reinforced concrete continuous beam specimens were designed,one of which was taken as a comparison specimen at room temperature to carry out a static load test on its bearing capacity at room temperature.A large scale fire simulation test system was used to test the shear behavior of the remaining 4 reinforced concrete continuous beams after fire.In general,continuous beam specimen is usually applied in the form of three face,all around the fire,by raising the temperature of the ISO834 standard heating up curve in order to develop the control work,focus on thinking about the influence of parameters such as fire condition,the cooling way,stay after the warming effect using natural cooling,water cooling after cooled to room temperature,the static load bearing capacity after fire effect test.To observe and analyze the law of crack development,failure mode of oblique section,bearing mechanism and residual bearing capacity of reinforced concrete continuous beam in shear and bending section after high temperature fire.Through the experiment,the following basic conclusions are drawn:(1)the measured results in the process of fire action on the specimen show that the highest temperature experienced by each measuring point in the section of the specimen occurs in the cooling process of about 1-15 min after ceasefire,showing a certain hysteresis phenomenon.Moreover,the closer to the measuring point in the beam section,the longer the hysteresis time to reach the peak temperature.(2)CWLLH1,LLH1-LLH4 are specimens designed according to the principle of "strong bending and weak shearing".The results of static load test show that all specimens are subject to shear failure of inclined section,that is,after 1.5 hours of fire action,the specimens are taken to be naturally cooled or watered.Compared with the specimens at room temperature,the failure forms of static load test are not significantly changed.(3)the results of static load test show that the fire condition affects the residual ultimate shear capacity to some extent.Compared with the specimens subjected to fire on three sides,the residual bearing capacity of the specimens subjected to fire on four sides is lower.For watering and cooling methods,LLH1 specimens subjected to fire on three sides have a residual shear capacity of 8.3% lower than that under normal temperature.LLH3 specimens subjected to fire in all directions have a residual shear capacity 18.8% lower than that of normal temperature specimens.For the natural cooling method,the remaining shear capacity of LLH2 specimens subjected to fire on three sides is 21.2% lower than that under normal temperature.However,LLH4 specimens subjected to fire in all directions have a residual shear capacity 26.6% lower than that of normal temperature specimens.(4)the test results show that the cooling mode also has a significant impact on the residual shear capacity of the specimen.Compared with watering cooling method,the measured ultimate static load of the naturally cooled specimen decreased more.For LLH1 test pieces that are subjected to fire on three sides and cooled by watering after being subjected to fire,their residual shear capacity is 8.3% lower than that of normal temperature comparison test pieces.The LLH2 specimen with natural cooling after fire has a residual shear bearing capacity of 21.2% lower than the normal temperature comparison specimen,and the residual bearing capacity of the natural cooling specimen is 12.9% lower than that of the watering cooling specimen.For LLH3 test pieces that are subjected to fire in four directions and cooled by watering after being subjected to fire,their remaining shear bearing capacity is 18.8% lower than that of normal temperature comparison test pieces.The LLH4 specimen with natural cooling under the action of fire has a residual shear bearing capacity of 26.6% lower than that of the normal temperature comparison specimen,and the residual bearing capacity of the natural cooling specimen is 7.8% lower than that of the watering cooling specimen.(5)the static load test results show that the measured vertical deformation of the continuous beam specimens with natural cooling after fire action is greater than that of the continuous beam specimens with watering and cooling under the same load level;The measured concrete strain of continuous beam specimens with watering cooling is greater than that of continuous beam specimens with natural cooling.(6)according to the fracture development of static load test,namely,the failure pattern shows that the obvious oblique crack subjected to shear failure at room temperature is less than that subjected to fire action,the main oblique crack is relatively concentrated,and the horizontal projection length of oblique crack is smaller than that of the specimen subjected to fire action.(7)The results of static load test show that the main oblique cracks caused by shear failure mainly occur in the shear and bending section between the middle support and the mid-span loading point in the continuous beam specimens subjected to fire.The development of the main oblique crack is accompanied by the splitting crack along the longitudinal bar at the root of the oblique crack.Under the action of fire on three sides,the splitting crack along the longitudinal bar appears at the bottom of the beam under the action of fire,while under the action of fire on four sides,the splitting crack along the longitudinal bar appears at the top and bottom of the beam under the action of fire.