High-Order Approach for the Control of Edge Stresses in RC Beams Strengthened with FRP Strips

Abstract

A closed-form high-order analytical model for the investigation of various methods that control and reduce the stress concentrations at the edges of reinforced concrete (RC) beams strengthened with externally bonded fiber-reinforced plastic (FRP) strips is presented. The model provides the means for the analysis of RC beams retrofitted with composite strips with a general variable width or thickness. Furthermore, it includes the effect of a “spew-fillet” and the influence of external anchoring devices such as vertical prestressed straps or clamps. The analysis includes the local and the overall response of the structure and focuses on the stress concentrations that arise at the edges of the bonded strip and in many cases lead to a brittle and premature failure of the strengthened member. The governing equations along with the boundary and continuity conditions are derived using the variational principle of virtual work and follow the high-order theory. Numerical solution via the multiple points shooting method is adopted when variable coefficients are involved and the concept of substructuring is introduced for reducing the required computational resources. Numerical investigation of various width and thickness profiles for the FRP strip and their influence on the stresses at the edge region is presented. In addition, the effects of the spew-fillet and the various anchoring devices are studied. The results reveal that proper use of such means can significantly reduce the edge stresses and thus prevent the brittle mode of failure. The paper is concluded with a summary and recommendations for the analysis and design of strengthened members.