Research On Mechanical Performance Of CFRP Strengthened Concrete-filled Steel Tube Columns After Exposure To High Temperature

At present,Concrete-filled steel tube columns are widely used in high-rise buildings due to their superior mechanical performance.High-rise buildings are densely populated with people and goods,and fires are frequent,and the mechanical performance of concrete-filled concrete-filled steel tube columns will be reduced to different degrees under high temperature environment,which affects the function of concrete-filled steel tube columns after fires.Reinforcement treatment of concrete-filled steel tube columns after fire can restore its mechanical performance.Carbon fiber reinforced plastics(CFRP)has the advantages of simple construction and good reinforcement effect,so it is widely used in concrete structures,but there are few studies on reinforcing concrete-filled steel tube columns after exposure to high temperature.Therefore,this paper carries out axial pressure test research,theoretical analysis and numerical simulation on CFRP strengthened concrete-filled steel tube stub columns after exposure to high temperature,and study of seismic performance of CFRP strengthened concrete-filled steel tube columns after exposure to high temperature based on OPENSEES software.is to provide test data and theoretical basis for the application of CFRP strengthened concrete-filled steel tube columns after exposure to high temperature.The main contents of this paper include the following aspects:(1)Material performance tests were conducted on steel and concrete after exposure to different temperatures to study the effects of temperature on the damage morphology and mechanical performance of steel and concrete,and electron microscope tests were conducted on concrete materials after high temperatures to study the laws of temperature effects on the internal structure of concrete.The test results showed that the yield strength of steel and compressive strength of concrete decreased with the increase of temperature.The observation of the concrete electron microscopy test shows that the cement matrix is severely damaged under the influence of temperature,the internal structure is loose,and the internal deterioration of concrete is serious.(2)With the number of CFRP strengthened concrete-filled steel tube columns after exposure to high temperature as variables,axial compression tests were carried out on 18 CFRP strengthened concrete-filled steel tube stub columns after high temperature,2 concrete-filled steel tube stub columns at room temperature and 6 concrete-filled steel tube stub columns after high temperature,and the test results showed that the bearing capacity and stiffness of concretefilled steel tube stub columns decreased with the increase of temperature,and the concretefilled steel tube stub columns at different temperatures were shear damage and waist drum damage when they were damaged.Compared with the unreinforced high temperature concretefilled steel tube stub columns,the CFRP strengthened concrete-filled steel tube stub columns after exposure to high temperature has a greater increase in bearing capacity and stiffness.The width of CFRP fracture decreases with the increase of the number of CFRP layers.Based on the experimental results and the limit equilibrium theory,considering the influence of temperature and CFRP restraint,the load bearing capacity calculation model of CFRP strengthened concrete-filled steel tube stub columns after exposure to high temperature is established.(3)Based on the ABAQUS platform,a finite element analysis model of CFRP strengthened concrete-filled steel tube stub columns after exposure to high temperature is established,and the reliability of the model is verified by combining with the test results,and the stress development law of CFRP strengthened concrete-filled steel tube stub columns after exposure to high temperature at each stage is studied by combining with the change law of loaddisplacement curve to further verify the synergistic working law among the components in CFRP strengthened concrete-filled steel tube stub columns after exposure to high temperature.(4)Based on OPENSEES platform,a model of CFRP strengthened concrete-filled steel tube stub columns after exposure to high temperature was established to study the influence of each variable on the seismic performance of CFRP strengthened concrete-filled steel tube stub columns after exposure to high temperature with temperature,number of CFRP layers,axial compression ratio,length-diameter ratio,concrete strength,steel tube thickness and steel tube yield strength as variables.