Experimental tests on the out-of-plane response of RC columns subjected to cyclic tensile-compressive loading

Over the last few years the increasing demand of housing for low income population in Colombia and several neighboring countries, associated to the significant increase of cost of land, has prompted construction companies to build medium to high rise reinforced concrete (RC) wall buildings. Most of these new residential buildings are constructed with walls that have thicknesses as low as 80 mm and are only lightly reinforced. The recent earthquakes in Chile (2010) and New Zealand (2011) have caused significant damage to some of the RC walls, some of which tended to buckle out-of-plane. In Colombia the wall thicknesses are significantly thinner than in Chile or New Zealand and is therefore is to be feared that these buildings may present the same out-of-plane failure mode during a future earthquake. Furthermore, many of the walls have only a single vertical reinforcement layer, which could increase the out-of-plane instability, as it will be shown in this paper. Although recent experimental tests have shown that wall out-of-plane deformations can extend throughout a relatively large part of the wall length, the boundary regions are the critical zones that control the development of associated failure modes. For thin walls behaving predominantly in flexure those boundary regions are subjected to mainly axial strains, and hence testing equivalent RC columns under cyclic axial tension and compression provides direct insights into the influence of the parameters triggering wall instability and possible out-of-plane failure. Within a collaborative project between the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland and the Universidad del Valle, the EIA University, and the University of Medellin in Colombia, equivalent RC columns with a single vertical reinforcement layer are tested at EPFL in order to investigate the effect of loading history, reinforcement ratio and eccentricity of the longitudinal rebars with regard to the element axis ration the out-of-plane response. The paper presents the details of this recent experimental campaign, describing the geometry and the reinforcement layout of the specimens, the test setup, the extensive instrumentation used, and the results obtained from the first tests. The experimental findings allowed to draw initial conclusions on the development of the out-of-plane instability, on the particularities of single layer reinforcement members and on the development of out-of-plane failures.