A coupled environmental-mechanical damage model for structural analysis of RC constructions

The aim of this work is to assess the collapse safety of both new and existing reinforced concrete structures. The latter can also be subjected to environmental degradation process. To this aim the behavior of concrete and reinforced concrete structures eventually degraded by physical-chemical attacks need to be accurately described with theoretical and numerical models that can take into account the main characteristics of this kind of structures. In this work a coupled environmental-mechanical scalar plastic-damage model originally developed by other authors was modified, enhancing both the mechanical and the environmental aspects. In particular an innovative formulation able to account for the physical deterioration mechanism due to freeze-thaw cycles was developed within the framework of the environmental damage approach, while a more comprehensive representation of the mixed tension-compression domain and an enhancement of the plastic evolution law were proposed within the framework of the mechanical damage approach. To validate and calibrate the mechanical damage model, it was applied to reproduce different tests taken from literature. Particular attention was dedicated in reproducing the Kupfer tests and the response of a Single-Edge-Notched beam, typical example of mixed-mode failure. In both cases experimental and numerical results compare well, demonstrating the ability of the model to predict structural response and crack patterns of such examples. To simulate the inelastic behavior of reinforced concrete panels, an efficient membrane model was proposed assuming superposition of different membranes (i.e. concrete and an appropriate number of steel bars). On the other hand, to assess the nonlinear behavior of reinforced concrete plates, an efficient plate model was proposed following a layered approach. Concerning the environmental aspect, the coupled environmental-mechanical damage model was calibrated by using a limited number of tests carried out on concrete specimens under mono-axial and bi-axial compressive stresses, subjected to freeze-thaw cycles with different levels of deterioration. Finally the proposed coupled model was used as a predictive tool both for simulating a different series of biaxial concrete specimens subjected to freeze-thaw cycles and to evaluate the load carrying capacity of a frost damaged beam.