CrackingofR/CtensilemembersreinforcedbyFRP-plates

The role of FRP-composite plates for strengthening of reinforced concrete structural elements subjected to axial loads is analyzed, with particular emphasis to the evolution of crack pattern and its conse- quences on tensile deformability. A non-linear model is developed, where cohesive stresses in concrete across cracks, non-linear bond-slip between steel bars and concrete, and linear constitutive laws at the concrete-FRP interface are considered. The non-linear governing equations are solved via finite difference method. A nu- merical example is presented, simulating a test with displacement control on a plated and an unplated rein- forced concrete member, where the evolution of the crack pattern along the tensile member is followed. The example confirms that external FRP-plating can be effective in reducing crack width and, consequently, in in- creasing stiffness of tensile members. This is mainly due to the fact that the transfer length of bond-slip phe- nomenon at the concrete-plate interface is significantly smaller than the concrete-steel bar counterpart. I INTRODUCTION serviceability limit states. As far as theoretical studies are concerned, solu- External plating by means of Carbon or Glass Fiber tions based on simple shear-lag models (as initially Reinforced Plastics (FRP) plates or sheets is one of proposed by Volkersen 1938), are not in general suf- the most promising and efficient reinforcement ficiently accurate. Neglecting bending of bonded techniques for axial, bending or shear strengthening plates, shear-lag models do not allow to compute the of reinforced concrete (RIC) elements. FRP rein- so-called secondary stresses, such as the peeling forcement is considered effective both in increasing stress, which are often very important since they can ultimate loading and in reducing deformability due represent the onset of plate debonding. to crack opening.