Study On Deformation And Cracking Performance Of RC Beams Strengthened By Bonded Frp

Bonding FRP technique consists of EBR and NSM reinforcement. Ithas many advantages than existing techniques. So it is also verynecessary to check the serviceability limit states of the strengthenedmembers. Experimental investigation and theoretical analysis are done inthis paper for deformation and crack of RC beams strengthened bybonding FRP. The main research contents and results are as follows.1. Experimental investigation. Thirteen full-size simply supportedrectangular section reinforced concrete beams were made in thisexperiment (one was a reinforced concrete beam, another six werestrengthened with NSM CFRP, and the rest eight were reinforced by theexternally bonded carbon fiber sheet or plate). Deflection and crack ofthe strengthened beams were observed and measured in the wholeexperimental course. Both the experimental results were analysed.2. Analysis of flexural characteristic number and reinforcementdesign. For RC beams strengthened with bonded FRP, compressedconcrete on cross section has not crushed in the states of both yieldingand FRP rupturing. The resultant force of compressed concrete and itslocation are simplified in this paper. Then approximate expressions areproposed to calculate the bending moments in both states above. Thepredictions of the simplified procedures agree well with the experimentalvalues. In addition, a simplified design method is presented for theFRP-strengthened RC beams to resist rupture of FRP.3. Analysis of deflection. The relationship of load- deflection isseparated into three stages: before cracking, from cracking to yielding,from yielding to breaking. For strengthened beams unloadingincompletely, the stage from cracking to yielding should be divided intotwo parts corresponding with states before and after strengthening. Thecurvature in every stage above is defined firstly, then the effectivestiffness and deflection in the midspan of the strengthened RC beamscould be calculated. The effect of preload is considered in the analysis above. And the theoretical predictions agree well with the experimentalvalues.4. Analysis of crack. According to theory of crack design in GB50010-2002, the crack of RC beams strengthened with FRP is analysed inthis paper. Influence coefficient of fracture interval and reinforcementstress and uniformity coefficient of reinforcement stress are defined inthis paper, then the expression of crack calculation similar as that inGB50010-2002 is brought forward. Preloading influence coefficient ofmaximum crack width is obtained through fitting with experimental datas.Then the design formula of mixmum crack width is brought forward forpreloaded RC beams strengthened with externally bonded FRP. And thetheoretical predictions agree well with the experimental values.