Özet:

Carbon fiber reinforced polymer (CFRP) laminates were proved as very effective method for either repairing or strengthening of used structures. However, the literature has no enough information about the behavior of RC continuous (two-span) T-section beams strengthened with CFRP laminates, especially in hogging moment zone (HMZ). This paper examines the effect of CFRP laminates lengths, used for strengthening of the hogging moment zone, upon the behavior of such beams, to determine the optimum strengthening length. 3-D theoretical models using the Finite Element (FE) Package ANSYS are used. The paper contains the main details of the FE modeling process; used element types, material properties, meshing, yield criterion and boundary conditions. The results of the proposed FE model were compared with those of a previous experimental research and very good agreement was found between both FE and experimental results. Three parameters were used in the parametric study; CFRP length, CFRP thickness, percentage ratio of the steel reinforcement (different diameters for reinforcement steel bars). To examine the effect of changing CFRP strengthening lengths, different types of results for the proposed parametric study were obtained for better understanding of behavior. Adding to this, these results were compared and analyzed at different stages of loading between first cracking of the RC studied T-beams and their failure. These results include load-deflection curves, bending moment diagrams, stresses and strains of the CFRP laminates, stresses and strains of steel reinforcement bars, redistribution of moments, energy dissipation, ductility, shear (bond) stresses and failure modes of the studied beams. It can be concluded that changing CFRP length in the HMZ is very effective upon the overall behavior of T-section continuous RC beams. This effect begins after first crack and considered as effective after the yielding of upper steel bars. Increasing the lengths of CFRP laminates increases capacity, ductility and energy dissipation of strengthened beams in the hogging moment zone. Also, it improves utilizing of upper steel bars and redistribution of moments between sagging and hogging moments. Practically, Design-Codes of using CFRP in strengthening of structures concern only with both CFRP strengthening length and its corresponding anchorage length. As a result, definitions of both optimum CFRP strengthening length and CFRP anchorage length were expressed. Finally, criteria to calculate both of them were concluded

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