Finite Element Analysis of the Flexural Performance of ECC-Concrete Composite Beams Reinforced with GFRP-Steel Composite Bars.

GFRP-reinforced concrete structures often suffer from insufficient ductility and limited crack control capability. This study investigates the flexural behavior of ECC-concrete composite beams reinforced with steel-FRP composite bars (SFCBs) using finite element analysis. A three-dimensional nonlinear finite element model was developed in ABAQUS and validated against four-point bending tests of eight composite beam specimens. The model incorporated a bilinear constitutive relationship for SFCBs and a cohesive interface model to simulate the interaction between ECC and concrete. Based on the validated model, the effects of reinforcement type and ECC replacement height on the flexural performance of composite beams were evaluated. The results showed that the proposed model accurately reproduced the load-deflection responses, strain development, and failure processes of the tested beams. The reinforcement type significantly affected the overall structural behavior, resulting in different load-carrying characteristics and deformation responses. Increasing the ECC replacement height mainly improved the cracking resistance by increasing the cracking load and promoting a more uniform crack distribution, while its effects on the yield and ultimate loads were limited. ECC primarily contributed to crack control and damage mitigation, whereas SFCBs influenced the overall load-carrying behavior of the composite beams. These findings provide insights into the design and performance evaluation of ECC-concrete composite beams reinforced with SFCBs.