Load-dependent composite action for beam nonlinear and ductile behavior

Ductile performance of beam structures often is achieved by material yielding or progressive failure of components. A new structural concept was developed and validated in this study to provide ductile responses of beam structures through load-dependent composite action resulting from the change in the modulus of shear connection. Layered beam specimens made from linear elastic fiber-reinforced polymer (FRP) members shear-connected by a nonlinear elastoplastic adhesive were tested to demonstrate this concept. Evidenced by the shear slip between the beam layers and the section strain distribution, the decrease in beam stiffness and thus the ductile load-displacement response originates from the reduced composite action between the beam layers. Recovery of the beam residual deformation after unloading occurred because of the nonlinear elastoplastic behavior of the adhesive. Finite-element (FE) modeling was conducted and well described the ductile load-displacement response and the change in composite action. Parametric studies were carried out to clarify the effects of adhesive modulus and strength on the load-dependent composite action and overall ductile performance. FE modeling was conducted to demonstrate the applicability of the concept for further engineering practice.