Bending Behavior of Reinforced Concrete Beams Strengthened with Composite Materials Using Inelastic and Nonlinear Adhesives

The bending behavior of reinforced concrete beams strengthened with composite materials externally bonded using nonlinear and inelastic adhesives is analytically investigated. A mathematical nonlinear model that uses the concepts of the high order theory and incorporates nonlinear and inelastic shear stress-shear angle behavior of the adhesive material is derived. The model is derived via the principle of virtual work along with the compatibility conditions, the constitutive laws, and the closed form solutions of the stress and displacement fields of the adhesive. The nonlinear governing differential equations are solved numerically for the case of elastic nonlinear adhesives and via an iterative procedure for cases that involve elastic-perfectly plastic adhesives. The unloading/reloading aspects of the inelastic structure are also considered. A numerical study of two beams strengthened with composite strips bonded using linear-elastic, nonlinear-elastic, and elasto-plastic adhesives is presented, discussed, and compared to finite element analysis. The results imply that the use of such adhesive materials improves the overall load carrying behavior of the strengthened beam, increases its ductility, provides the mechanism for the formation of plastic hinges, and reduces the shear stresses near the ends of the bonded strip.