Uncertainty in the inelastic behavior of reinforced concrete walls due to material properties

Abstract

Reinforced concrete (RC) walls are structural elements widely used to resist lateral forces in highly seismic countries. Design codes provide minimum requirements to ensure an adequate performance of shear walls during ground motions; however, during recent earthquakes such as the 2010 Maule earthquake in Chile, or the Canterbury, Christchurch 2010 and 2011 earthquakes in New Zealand, some shear walls underwent an unprecedented and somewhat unexpected brittle failure. This fact evidenced that current analysis and design procedures for shear wall buildings do not provide a close representation of the true seismic response of these walls under severe cyclic earthquake loading, which is an imperative in performance-based design. Keeping that in mind, the present research implemented a Nonlinear Finite Element Wall (NLFEW) model, which was validated using parametric analyses. A micro-model using layered-shell elements was selected that uses an effective material model for concrete based on theory of plasticity and continuum damage mechanics. The wall model was validated simulating the behavior of four experimental RC benchmark wall test specimens subjected to quasi-static cyclic loads. Five response parameters were considered to evaluate the accuracy of the model: the initial stiffness, peak base-shear force, peak displacement at the top, ultimate base-shear force, and energy dissipated throughout the cyclic loading. The same parameters were used to quantify the uncertainty generated by the material properties in the global response of each wall. Results show that the model fits very well the experimental tests, and localization of damage is correctly predicted. Moreover, results from sensitivity analyses suggest that the initial stiffness is mainly influenced by variables of concrete in tension; the maximum top displacement (ductility of the element) depends largely on the parameters of concrete in compression; and base-shear forces and dissipated energy are sensitive to the post-yield stiffness of steel reinforcement.