Capacity assessment of uncorroded and corroded dapped-end beams by NLFE and strut-and-tie based methods

The verification of dapped-end beams degraded by corrosion is a problem, especially for existing bridges in service. This paper proposes a nonlinear finite element (NLFE) modeling procedure and a simple strut-and-tie based procedure for predicting the response of dapped-end beams subjected to chloride corrosion. Firstly, the finite element modeling strategy, based on the adoption of multilayer shell elements and the PARC_CL 2.1 crack model is described. Then, the degradation effects on concrete, rebars, and steel-to-concrete interaction are defined as a function of the propagation period of corrosion. In particular, the effects of corrosion on the reinforcement are modeled by applying a reduction of tensile strength that considers for both the reduction of cross-section and the ultimate strain caused by pitting. Concrete splitting cracking due to volume expansion during rust formation is modeled by reducing the mechanical properties of concrete. Corrosion effects in steel-to-concrete interaction are modeled by applying a bond strength decay to the spring elements connecting corroded rebars-modeled with truss elements-and concrete multilayer shell elements. The proposed finite element procedure is used to study two scenarios based on different spatial distributions of corrosion-prone areas. Subsequently, a simplified analytical approach based on the strut-and-corroded tie method-called S&CT method-is proposed and compared with the finite element outcomes. Finally, the validations of the two proposed methods are presented with respect to a corroded dapped-end beam, showing that corrosion of rebars affects the resistance mechanisms of the dapped-end beam, by reducing both resistance and ductility. The proposed simplified analytical S&CT method provides conservative and safe results compared to the numerical NLFE model and to experimental data.