Thermodynamic model of life-cycle deterioration of seismic resistance for complex RC structures by coupling corrosion and cracking damage

The durability and service life of reinforced concrete (RC) structural components in bridges and frames are limited by the susceptibility of the reinforcement to corrosion. Corrosion leads to a reduction in the cross-section of the rebar and degrades its material properties. Severe corrosion and damage to stirrups can trigger buckling of the longitudinal bars. Additionally, it has been reported that concrete cracking, caused by mechanical forces, accelerates the corrosion process. The fundamental cause or driving force for all corrosion is the lowering of the system's Gibbs energy. Based on a lumped damage model and the theory of the thermodynamics of solids, coupling relations of three internal variables (concrete cracking damage, reinforcement plasticity, and corrosion level) are proposed. This macro -model also allows for considering buckling of longitudinal bars and loss of confinement due to corrosion of the transverse reinforcement. By combining available time -dependent corrosion laws with lumped damage constitutive equations, it is possible to predict the life -cycle resistance of RC bridge columns and frames and simulate their behavior when subjected to extreme loading in a corrosive environment. Earthquake forces are considered as an example of such kind of extreme loading. The thermodynamic formulation extends the range of applicability for the available corrosion laws in the literature by including the influence of concrete cracks. Two parametric examples demonstrate the potential applications of the model, including the estimation of critical mass loss for specific structures and the reduction of service life after medium -intensity earthquakes. The accuracy, effectiveness, and computational efficiency of the proposed model are fully verified in terms of the comparisons of experimental and numerical results.