Lateral buckling in reinforced concrete walls

Structural walls are used worldwide to resist gravity and earthquake loads. In many countries, structural walls commonly are constructed with a rectangular cross section, or a cross section made up of interconnected rectangles, without an enlarged boundary element. In some countries, design practice has resulted in walls that are more slender than those used in the past. For example, in Chile and elsewhere it is not unusual to find rectangular wall edges having thickness of 6 to 8 in. (150 to 200 mm), resulting in floor-to-floor slenderness ratios reaching h_u/b = 16 or greater. Such walls can be susceptible to overall wall buckling in which a portion of the walls buckles out of the plane of the wall. Examples of this behavior were observed following the 2010 Chile earthquake. Tendency to buckle is believed to depend primarily on the wall clear height to thickness ratio h_u/b and loading history. Two failure modes are hypothesized. One hypothesis is that tensile yielding for loading in one direction softens the boundary for subsequent loading in the opposite direction, leading to lateral instability of an otherwise intact wall. A second hypothesis is that the wall crushes first, leaving an even smaller and irregular cross section. This crushed section may become immediately unstable or, alternatively, subsequent tension and compression cycles may lead to instability of the reduced cross section according to the first hypothesis, leading to a secondary buckling failure. A theory is presented for buckling of sections subjected to inelastic tension and compression strain cycles. The theory is applied to tests of reinforced concrete prisms and one Chilean building (Alto Huerto), which had a buckled wall following the 2010 Chile earthquake. Based on this study, it is concluded that buckling most likely was a secondary failure that occurred after initial crushing of the wall boundaries.