Parametric space for the optimal design of compression-yielding FRP-reinforced concrete beams

Ductility of flexural members reinforced with fiber reinforced polymer (FRP) has been a serious concern for the application of FRP in structural engineering. A new and effective structural design concept of achieving ductility for FRP-reinforced concrete beams through compression yielding (CY) instead of tensile yielding has recently been developed. The ductility of CY beams depends very much on the details of the CY zone. A previous theoretical investigation into beams with an elastic-perfectly plastic CY block has shown that an optimal level of ductility exists in certain regions of the parametric space. However, experimental investigations have found that elastic-perfectly plastic CY blocks are difficult to construct, and often the post-yield behavior features some strain hardening or softening. For this reason, the present study aims to clarify the ductility behavior of CY beams with a more general CY block model, focusing on the effects of the post-yield modulus of the CY block. The key variables of the CY beam system are first identified. Subsequently, the ductility performance of CY beams is investigated using a combination of analytical study and numerical simulation. Finally, the parametric space that produces an optimal level of ductility is further identified which could form the basis for the optimal design of CY beams. The results demonstrate that a small post-yield modulus of the CY block can be beneficial for ductility performance. However, a large post-yield modulus will significantly reduce the ductility.