Fire Resistance Of EBR-DFRP Strengthened RC Beams And Flexural Behaviors In Fire

Carbon Fiber Reinforced Polymer(CFRP)is a new kind of reinforcement material with superior properties,which is widely used in the reinforcement of reinforced concrete structures.The most widely used form is Externally Bonded Reinforced(EBR).However,the weak fire resistance of CFRP seriously impedes the popularization and application of this technology in civil engineering.Therefore,it is very important to study the fire resistance of EBR-CFRP strengthened structure and propose sound fire-resistant design theories.In this paper,the thermo-mechanical coupling finite element model was established by using ABAQUS,and the bond-slip relationship of CFRP-concrete at high temperature was employed to simulate the whole process of debonding failure of EBR-CFRP strengthened reinforced concrete beam under high temperature.The average bond shear stress and slip of CFRP-concrete interface varied with the duration,among which the bond shear stress was less affected by temperature and was greatly affected by the external load and bond length.The slip time was related to the distribution of temperature and was less affected by external loads.At the same time,a lot of parametric analyzes were carried out through the finite element program.It was found that the load ratio,insulation thickness,bond length,fire condition and anchorage had a great influence on the fire resistance of specimens.It could increase the bonding strength of CFRP-concrete interface and improve the fire resistance effectively to set anchoring layers at both ends of the CFRP sheet.Finally,based on the result of the finite element analysis,a regression formula for predicting fire resistance of EBR-CFRP strengthened reinforced concrete beam was put forward,which could be used in structural design.In addition,the finite element analysis of cross-section heat transfer was conducted at the same time.The main parameters influencing the temperature of the cross sections of beams were analyzed.A new method,"equivalent-concrete-method",was proposed to predict the temperature of the cross sections of beams with insulations.On this basis,a mechanical model of EBR-CFRP strengthened reinforced concrete beam under fire was established.The time dependent flexural capacity of EBR-CFRP strengthened reinforced concrete beam was calculated.The fire resistance of the specimens could be estimated by comparing the time dependent flexural capacity with the external load.Therefore,this method could provide a new way for the fire design of EBR-CFRP strengthened reinforced concrete beams.