An analytical model for the evaluation of the local ductility of R/C members

The evaluation of the local and global ductility of reinforced concrete (R/C) structures constitutes a basic theme in the structural engineering, analyzed and discussed for a long time. Nowadays this issue can be still considered of topical interest, mainly in the framework of non-linear or performance-based methodologies, very common in the current design approaches. In this paper a simplified analytical procedure is proposed for the evaluation of the plastic capacity of a reference element subjected to axial force and bending moment. The procedure is based on the model of a R/C element included between two subsequent cracks and describes the relationship between the generalized force (axial force or bending moment) and the mean deformation of the block. The evaluation of the strength and mainly of the ductility characteristics of R/C elements take into account all the relevant non-linear phenomena, namely the concrete cracking, the non-linear behavior of the materials, the tension stiffening effects, the slip presence at the steel-concrete interface and the steel strain localization near the cracks after yielding. The validation of the proposed model is carried out through comparisons with experimental and numerical results available in the literature. The relationship defined between the force and the mean deformation is applied for the non-linear analysis of simple structures up to the collapse, and to estimate their plastic capacity.