Stiffness degradation model of thin and lightly reinforced concrete walls for housing

The stiffness of structural walls is a key parameter for seismic design because the distribution of shear forces depends on the relative stiffness of each wall of the structural system. The study of stiffness degradation of low-rise reinforced concrete walls has been focused on the description of the deterioration of such structural property. This study aims at proposing a semi-empirical model for assessing the lateral stiffness degradation in terms of drift ratio of thin and lightly reinforced concrete walls for low-rise and low-cost housing subjected to seismic demands. The variables of the study are the height-to-length ratio of walls (0.5, 1 and 2), type of concrete (normal-weight, light-weight and self-compacting), steel ratio of web shear reinforcement (0.125% and 0.25%), and the type of web shear reinforcement (deformed bars and welded-wire meshes). The experimental program comprises 23 walls tested under quasi-static reversed-cyclic loading. Lateral stiffness computed using measured response of walls are compared with stiffness computed using recommendations prescribed by codes or reported in a literature review. The effect of geometrical and mechanical properties of walls on stiffness is also assessed in the paper. In addition, the study proposes limit values of stiffness degradation for different limit states and performance levels.