An improved damage plastic model for RC structure FE modelling under cyclic loading conditions

The damage evolution law is crucial for the concrete damaged plasticity (CDP) model, especially when modelling reinforced concrete (RC) structures under cyclic loading. However, the unloading-reloading behaviour of the concrete could not be adequately tracked with the prevalent method for determining damage variables within the CDP framework using constant strain ratio factors. To address this issue, this paper proposes a new function based on the existing database to replace universally used constant strain ratio factors, aiming to improve the capability of the damage evolution law in accurately describing the cyclic behaviour of concrete. The proposed functions are implemented into the CDP model, developing an improved CDP model. Also, for capturing the failure zone of RC structure finite element (FE) models, a damage-based element failure criterion is proposed. Different RC structure behaviours under cyclic loads are modelled and compared against test data. The results indicate that the improved CDP model could offer better predictions rather than the original CDP model. Furthermore, quantitative indexes for assessing the ultimate state of RC structures are also suggested by numerical investigation of the failure mechanism of the RC frame structure.