Behavior of reinforced concrete shear wall buildings subjected to large earthquakes

Abstract

Frame systems are the preferred structural systems in most seismic regions, where they are sometimes also combined with braces or walls. On the other hand Chile, one of the most seismically active countries in the world, is an exception to this practice. Any Chilean residential building higher than 5 stories is almost completely made up of reinforced concrete shear walls. Surprisingly, only 2% of the residential building inventory subjected to the 2010 Chile earthquake (Mw 8.8) suffered severe damage, even though many structures were affected by ground accelerations larger than those prescribed in the Chilean seismic design code. This observation suggests that there is a large (and unintended) overstrength in this type of buildings. In a previous study, the authors showed that some of the traditional sources of overstrength mentioned in the literature could explain the lack of damage in low rise buildings but not in taller structures. Motivated by this observation, representative tall buildings were reanalyzed using more realistic models (e.g., flexural capacity of the walls assessed by fiber models) in order to get more insight into their actual seismic capacity. Two actual buildings of 17 and 26 stories that survived with no damage the 2010 Chile earthquake were analyzed by response history analysis. Results show that consideration of wall flanges (usually omitted in practice) cannot explain the lack of damage. On the other hand, it is observed that good performance might be a consequence of possible foundation uplift. Finally, the analyses also suggest that, even when there is no damage, elastic analysis has limitations to reproduce the actual observed behavior.