Özet:

Strengthening, repairing and rehabilitation of existing structures are very important functions of the construction industry nowadays. Laminates made of Carbon Fiber Reinforced Polymers (CFRP) have proved an excellent behavior when used for the strengthening, repairing and rehabilitation of existing structures. When CFRP laminates 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 moment zone (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 occur in such structures; crushing of concrete, debonding between CFRP laminates and concrete surfaces, and rupture of CFRP laminates. Each failure mode is conducted according to a certain criterion which is a function of both mechanical properties of materials (concrete, reinforcement, CFRP, and adhesive) and dimensions of both RC beam and CFRP strengthening laminates. This paper explains the sequence of occurring of the different failure modes of RC continuous T-beams of two spans strengthened using CFRP laminates either in SMZ or 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 and the explanation of the different mechanisms of the failure modes of the strengthened beams. Studied parameters include CFRP length, thickness, width and locations of CFRP laminate across the flange of the studied T-beams. Also, unstrengthened (control) beams were studied to compare the results with the strengthened ones for better understanding of the effect of CFRP strengthening upon the behavior of the studied T-beams. ANSYS which is a very powerful FE tool is used to create 3-D models of this study. It was found that CFRP dimensions are the principle factors that affect the type of the failure mode occurred in the strengthened beam. Rupture occurs, only when strengthening of the HMZ, if the CFRP stress reaches its maximum value (strength) by using very small CFRP thickness comparing with the corresponding length. Debonding of CFRP laminates occurs if shear stress, in the adhesive (contact) (bond layer) between the laminate and the concrete, reaches its maximum value. Crushing of concrete occurs as a final stage after yielding of steel reinforcement, formation of a plastic hinge, moment redistribution till the capacity of the beam is reached which means failure. 

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