OPTIMUM CFRP LENGTH FOR THE HOGGING MOMENT ZONE (HMZ) OF CONTINUOUS RC T-BEAMS

Abstract

Carbonfiber reinforced polymer (CFRP) laminates were proved as very effective methodfor either repairing or strengthening of used structures. However, theliterature has no enough information about the behavior of RC continuous(two-span) T-section beams strengthened with CFRP laminates, especially inhogging moment zone (HMZ). This paper examines the effect of CFRP laminateslengths, used for strengthening of the hogging moment zone, upon the behaviorof such beams, to determine the optimum strengthening length. 3-D theoreticalmodels using the Finite Element (FE) Package ANSYS are used. The paper containsthe main details of the FE modeling process; used element types, materialproperties, meshing, yield criterion and boundary conditions. The results of theproposed FE model were compared with those of a previous experimental researchand very good agreement was found between both FE and experimental results.Three parameters were used in the parametric study; CFRP length, CFRPthickness, percentage ratio of the steel reinforcement (different diameters forreinforcement steel bars). To examine the effect of changing CFRP strengtheninglengths, different types of results for the proposed parametric study wereobtained for better understanding of behavior. Adding to this, these resultswere compared and analyzed at different stages of loading between firstcracking of the RC studied T-beams and their failure. These results includeload-deflection curves, bending moment diagrams, stresses and strains of the CFRPlaminates, stresses and strains of steel reinforcement bars, redistribution ofmoments, energy dissipation, ductility, shear (bond) stresses and failure modesof the studied beams. It can be concluded that changing CFRP length in the HMZis very effective upon the overall behavior of T-section continuous RC beams.This effect begins after first crack and considered as effective after theyielding of upper steel bars. Increasing the lengths of CFRP laminatesincreases capacity, ductility and energy dissipation of strengthened beams inthe hogging moment zone. Also, it improves utilizing of upper steel bars andredistribution of moments between sagging and hogging moments. Practically,Design-Codes of using CFRP in strengthening of structures concern only withboth CFRP strengthening length and its corresponding anchorage length. As aresult, definitions of both optimum CFRP strengthening length and CFRPanchorage length were expressed. Finally, criteria to calculate both of themwere concluded