Stability of Slender Wall Boundaries Under Non-Uniform Strain Profiles

Abstract eng:
Prior 2010, out-of-plane instability in slender boundary elements subjected to cyclic loading had been observed in some experimental tests conducted on columns and walls but not in an actual earthquake. Later, buckling in slender walls was reported following the 2010 Chile and the 2011 New Zealand earthquakes. Structural walls have proved to be an effective system for the protection of buildings from strong earthquakes, and their design and use over the past decades has evolved in thinner and heavily stressed cross sections, which has pushed the boundaries for design to a critical point. Researchers have proposed in the past theoretical models for buckling of prismatic columns under uniform tension/compression cycles, where the key parameter is the maximum tensile strain prior buckling during load reversal. These models have shown good accuracy in comparison with experimental and analytical studies conducted on cyclically loaded columns under constant axial force. However, analysis of slender walls requires considering other aspects that influence the response. Walls have strain gradients along their length and height, and both effects must be considered for a more accurate estimation of the onset of out-of-plane instability. In some cases, the assumption of uniform axial strain along the wall height is reasonable. However, in the more general case, this assumption leads to an underestimation of the maximum tensile strain required to buckle the wall during load reversal and therefore to an overestimation of the minimum wall thickness required for design to prevent buckling from occurring. Moreover, the strain gradient along the wall length must also be considered for analysis. This paper presents the main findings of analytical studies conducted on isolated boundary elements and walls using two-dimensional nonlinear finite element models and nonlinear beam-column elements with force-based formulation, for the determination of the influence of the strain gradient along the wall length and height in the onset of out-of-plane instability. A simplified approach that can be used for pre-design purposes is proposed to evaluate the onset of out-of-plane instability in a variety of cases.

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