Research
Out-of-plane instability is identified as one of the failure modes of rectangular RC walls. This mode of failure was previously observed in experimental studies of rectangular walls, and has attracted more attention following the observed damage of several walls in the recent earthquakes in Chile and Christchurch.
In this study, out-of-plane instability of slender rectangular walls subject to in-plane loading is investigated. For this purpose, the ability and robustness of a finite element model in predicting nonlinear behavior and failure patterns, particularly out-of-plane instability of rectangular walls has been investigated. Experimental results of walls with different failure modes are used for model verification. The model is found to be able to reasonably capture the lateral load versus top displacement response of the specimens and predict most of the experimentally observed failure mechanisms of rectangular walls except bar buckling. The simulated failure patterns include shear, flexure, flexure-shear and flexure-out-of-plane modes, and the failure to predict bar buckling was expected due to inherent deficiencies of embedded bar elements and limitations of material models available in the program.
Using the validated model, some of the parameters known to be influential on out-of-plane instability of walls have been scrutinized, and the effects of these parameters on this mode of failure have been evaluated by testing three rectangular wall specimens subject to cyclic quasi-static loading. The specimens were half-scale, representing first story of four story prototype walls. The test setup was thus designed to apply the lateral load as well as the bending moment coming from the upper stories. The specimens were designed according to NZS3101:2006 and were different in thickness and length to investigate the effects of these parameters on the onset and extent of out-of-plane displacement of rectangular walls. The experimental results have been scrutinized in terms of significant stages of wall response observed during the test and the effects of the above-mentioned parameters on the sequence of these stages. Based on numerical investigations as well as experimental findings carried out in this research, design recommendations will proposed to reduce/prevent out-of-plane displacements of rectangular walls.
