Interface Performance Of Concrete And Seismic Performance Of Short Columns After Fire And Strengthened With CFRP

Fiber reinforced polymer/plastic (FRP) reinforcement method hasobvious technological advantages in light weight, high strength, convenientconstruction, liable quality etc. In recent years, FRP reinforcement methodhas been used in the renewal project of concrete structures after fire. Therehave been many studies on the interface properties between FRP and concretemember at room temperature and elevated temperature. However, the researchon the interface properties between carbon fiber reinforced polymer (CFRP)and concrete after fire has rarely been reported. At the same time, research onthe use of FRP to strengthen reinforced concrete structure after fire has madesome achievements, however, the shear performance of concrete column afterfire and strengthened with FRP has not been reported. So in the paper, thebonding behavior between CFRP and fire-damaged concrete and the seismicperformance of concrete short column (CSC) after fire and strengthened withCFRP are carried out. The main work and conclusions include as follows:1. The experimental studies of35test specimens were carried out toinvestigate the normal bonding property between CFRP and fire-damagedconcrete. The influence of high temperature, constant temperature time andtypes of cooling on the normal bonding strength were researched. The formulafor the normal bonding strength of concrete after fire with differenttemperature is given. The test results show that:(1) the normal bondingstrength is decreased with an increase of fire temperature. Comparing tonatural cooling, the normal bonding strength of water cooling specimens ismuch lower. Comparing to the specimens without fire, the normal bondingstrength of natural cooling specimens and water cooling specimens exposed to300℃and500℃high temperature declines4.1%、30.8%and11.0%、40.4%respectively.(2) The failure surface depth of specimens after fire is muchdeeper than the ones without fire. The reason maybe that the integrity ofconcrete at a certain depth under the interface strengthened by the permeation of carbon fiber adhesive.2. The shear tests of45specimens were carried out to investigate theadhesive interface performance between CFRP and fire-damaged concrete.The influence of bond length and width, layers, high temperature and types ofcooling on the shear bonding strength were researched. The bond-slipconstitutive relationship of CFRP-concrete after fire based on hyperbolicmodel and Popovics are introduced, and the formulas for characteristicparameters of curves are given. The test results show that:(1) While the firetemperature is less than500℃, with the bond length increasing, the ultimatebond load of specimen after fire go up first and drop after, both reach the peakwhen the bond length is130mm. While the fire temperature is500℃, theultimate bond load increases with increase of bond length.(2) The standardbond-slip constitutive relationship of CFRP-concrete after fire has the samecurve characters.3. The pseudo-static tests of concrete short columns after fire andstrengthened with CFRP were carried out to investigate the influence of CFRPusage and wrapping manner on strengthened seismic performance of CSCsafter fire. A practical calculation method for shear strength of concretecolumn after fire and strengthened with CFRP was suggested. The resultsshow that:(1) the shear strength of CSC wrapped with CFRP is increased by21.8%of that without wrapping. The shear strength of CSC firstly exposed tofire and latterly wrapped with CFRP is about111.2%~117.1%of that withoutfire action and without wrapping.(2) CFRP wrapping can enhance both thehysteretic energy dissipation and ultimate deformation of CSC without fireaction and after fire.(3) For the same CFRP usage, the shear strength ofcolumn wrapped entirely is slightly better than that wrapped with strips.(4)The hysteretic rules of CSC for the cases of without fire action, after fire,without strengthening and with strengthening are similar.