Seismic response of core walls – open questions after the earthquakes in Chile and New Zealand

Recent earthquakes in Chile (2010, M 8.8) and New Zealand (2011, M 6.3) have shown that, despite many years of extensive research and subsequent design code advancements, several modern reinforced concrete walls underperformed or even failed during these seismic events. Many of the walls that were damaged were non-rectangular walls or part of core walls, while past research had focused on walls with rectangular cross-sections. The observed wall failures included in particular compression failures and out-of-plane instabilities and triggered new research programs all around the world. This presentation presents two ongoing research projects at EPFL that address the seismic performance and design of reinforced concrete core walls. In the first project, the behavior of core walls when subjected to different loading directions is examined. Based on experimental and numerical studies, it is argued that the diagonal loading direction is the most critical one—although it is often neglected in design. In the second project, the out-of-plane failure mode is investigated. Recent EPFL wall tests were the first tests where the entire displacement fields of walls that developed large out-of-plane displacements were recorded by means of optical measurements. This novel data allowed new insights into this failure mechanism and the presentation highlights new findings and open research questions.