FAILURE MODES OF CONTINUOUS REINFORCED CONCRETE T-BEAMS STRENGTHENED USING CFRP LAMINATES

Abstract

Strengthening,repairing and rehabilitation of existing structures are very importantfunctions of the construction industry nowadays. Laminates made of Carbon FiberReinforced Polymers (CFRP) have proved an excellent behavior when used for thestrengthening, repairing and rehabilitation of existing structures. When CFRPlaminates are used to strengthen continuous reinforced concrete (RC) T-beams,they may be fixed either in the lower soffit of the beam in the hogging momentzone (HMZ); or in the upper surface of the beam, in the sagging moment zone(SMZ) in the vicinity of mid-supports. Three types of failure modes may occurin such structures; crushing of concrete, debonding between CFRP laminates andconcrete surfaces, and rupture of CFRP laminates. Each failure mode isconducted according to a certain criterion which is a function of bothmechanical properties of materials (concrete, reinforcement, CFRP, andadhesive) and dimensions of both RC beam and CFRP strengthening laminates. Thispaper explains the sequence of occurring of the different failure modes of RCcontinuous T-beams of two spans strengthened using CFRP laminates either in SMZor in HMZ. The paper contains the main details of the finite element (FE)modeling process, behavior of the strengthened beams either in SMZ and HMZ andthe explanation of the different mechanisms of the failure modes of thestrengthened beams. Studied parameters include CFRP length, thickness, widthand locations of CFRP laminate across the flange of the studied T-beams. Also,unstrengthened (control) beams were studied to compare the results with thestrengthened ones for better understanding of the effect of CFRP strengtheningupon the behavior of the studied T-beams. ANSYS which is a very powerful FEtool is used to create 3-D models of this study. It was found that CFRPdimensions are the principle factors that affect the type of the failure modeoccurred in the strengthened beam. Rupture occurs, only when strengthening ofthe HMZ, if the CFRP stress reaches its maximum value (strength) by using verysmall CFRP thickness comparing with the corresponding length. Debonding of CFRPlaminates occurs if shear stress, in the adhesive (contact) (bond layer)between the laminate and the concrete, reaches its maximum value. Crushing ofconcrete occurs as a final stage after yielding of steel reinforcement,formation of a plastic hinge, moment redistribution till the capacity of thebeam is reached which means failure.