Can shear walled structures and softening behaviour live together? Francesco Marmo 1 , Nunziante Valoroso 2 1 Dipartimento di Ingegneria Strutturale, Universit` a di Napoli Federico II, Italy E-mail: f.marmo@unina.it 2 Dipartimento per le Tecnologie, Universit` a di Napoli Parthenope, Italy E-mail: nunziante.valoroso@uniparthenope.it Keywords: Reinforced concrete, softening, pushover analysis. SUMMARY. The analysis of reinforced concrete structures accounting for softening behaviour of concrete in compression is presented. The mesh-objectivity issue is addressed using a fracture energy-based regularization in order to keep the computational effort reduced. 1 INTRODUCTION Nonlinear analysis of framed and shear-walled buildings are becoming more and more popular in practical applications for assessing the performance of reinforced concrete (RC) structures under seismic load action. In this context the correct description of material behaviour is of paramount importance in order to capture the structural failure mechanisms. In a companion communication [1] we show how, if properly implemented, the stress-strain relationships for concrete and steel pre- scribed by building codes allow one to effectively carry out the limit analysis of RC structures. How- ever, failure predictions require more refined constitutive laws accounting for softening behaviour of concrete in compression. In this work we present the results of a preliminary study in which full-scale structures are ana- lyzed using the so-called fracture energy approach [2] in order to simulate energy dissipation due to concrete crushing. This technique, that has been successfully used in many practical applications, basically relies upon the modification of the softening modulus depending on a characteristic length related to element size and enforces objectivity of mechanical dissipation at varying mesh density within a localization band of given width. Although well established only for the tensile cracking case, here fracture energy and characteristic length concepts are applied for compressive fracture of concrete. This is motivated by the fact that our main purpose is to implement strain softening via a stable and sufficiently refined approach yet maintaining a degree of complexity that keeps the problem workable for a designer with limited knowledge of material parameters of the structure to be analyzed. For RC structures a similar approach has been presented by Coleman and Spacone in [3] in the context of a multi-fiber methodology to deal with softening behaviour in compression for force- based frame elements, in which case strain localization occurs in a single quadrature point. Our implementation takes this idea one step further since the fracture energy regularization is herein used for the calibration of the constitutive relationship adopted for both beam and shell elements in which use is made of the fiber-free integration method [4] within a displacement-based formulation. Representative numerical examples are shown that illustrate the capabilities of the proposed ap- proach and allow useful considerations pertaining to the analysis of full-scale structures. 1