Seismic assessment of reinforced concrete buildings with coupled walls

Abstract

In Chile, most reinforced concrete (RC) buildings have a shear wall configuration, which in a large majority have performed well during recent earthquakes. However, a brittle failure was observed in RC walls in few buildings after 2010, Mw=8.8, Chile earthquake. This flexural-compressive failure was observed in RC walls located at lower stories. Inelastic dynamic analysis conducted recently demonstrated that these buildings remained essentially elastic until an abrupt failure occurred in RC walls. Therefore, investigating the elastic dynamic behavior of such buildings is critical to further understand the seismic behavior and the observed damage. Additionally, recent studies on resisting planes of RC buildings damaged during the Chile earthquake suggest that the behavior of the walls was highly influenced by the interaction of the resisting plane with the rest of the structure. Motivated by these hypotheses, the main objective of this research is to assess the coupling effect in walls considering the three-dimensional layout of RC buildings. The second objective is to analyze the effects of four modeling assumptions in the seismic demand of coupled RC walls. To achieve these objectives, detailed linear finite element models of three RC wall buildings damaged during 2010 earthquake are developed in ETABS and response history analyses are conducted applying ground motions in both horizontal directions simultaneously. From these analyses, the seismic demand of axial loads, shear forces, and bending moments along the height of several RC walls is investigated. Results show that the common design assumption of a cantilever wall implicit in design codes is inappropriate for this type of buildings. From this study it is concluded that the axial load of walls increases considerably due to coupling effect, with values that exceed an axial load ratio of 0.35, which corresponds to the limit imposed after 2010 Chile earthquake.