The research presented here seeks to address the key parameters influential on out-of-plane (OOP) instability of rectangular walls, which was observed in the 2010 Chile and the 2011 New Zealand earthquakes in some well-confined modern walls. For this purpose, a finite element model, previously verified for its capability to reliably simulate different failure modes of this type of structural walls, was adopted. The parametric matrix included a series of specimens designed to be tested by the authors and other specimens already tested by other researchers. The effect of slenderness (unsupported height-to-thickness) ratio, reinforcement ratio, length and axial load on the OOP response of these specimens is scrutinized using the predicted response of the boundary region longitudinal reinforcement at the elevation corresponding to the maximum OOP displacement in each case. For a given slenderness and longitudinal reinforcement ratio, development of a critical average tensile strain over a certain height can lead to formation of OOP instability in walls. Therefore, the effect of these parameters on the strain history, strain gradient along the wall height, as well as the stress–strain response of the longitudinal bars throughout the cyclic loading are evaluated and the variation of the OOP response attributable to the effect of each parameter is discussed. This parametric study indicated that the initiation of OOP displacement in doubly reinforced walls after unloading from a peak displacement and during reloading in the opposite direction is in line with the significant reduction of compressive stiffness (yielding in compression) in the boundary region longitudinal bars along a specific height (at least 60% of the wall height). Based on the findings of this study, an experimental campaign was designed and four of the parametric models were experimentally tested under in-plane cyclic loading. In addition to the parameters noted above, the effects of shear strength, boundary conditions and eccentricity of material properties across the wall thickness on the OOP response of the benchmark parametric model are also briefly discussed. The experimental observations as well as the numerical versus experimental comparisons are presented in a companion paper.

中文翻译：

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双重加固结构墙面外失稳的参数研究。第一部分：有限元预测

此处提出的研究旨在解决影响矩形墙的平面外（OOP）不稳定性的关键参数，在一些封闭良好的现代墙体中，2010年智利和2011年新西兰地震中就观察到了这些参数。为此，采用了有限元模型，该模型先前已经过验证其能够可靠地模拟这种类型结构墙的不同破坏模式的能力。参数矩阵包括设计用于由作者测试的一系列标本和已由其他研究人员测试的其他标本。细长比（不受支持的高度与厚度）比，增强比，在每种情况下，使用对应于最大OOP位移的标高处边界区域纵向钢筋的预测响应，仔细检查这些样品的OOP响应的长度和轴向载荷。对于给定的细长度和纵向增强比，在一定高度上形成临界平均拉伸应变会导致壁中OOP不稳定的形成。因此，评估了这些参数对应变历史，沿壁高的应变梯度以及在整个循环荷载下纵向钢筋的应力-应变响应的影响，并且归因于每种影响，OOP响应的变化参数进行了讨论。该参数研究表明，在从峰值位移卸载后以及在相反方向的再加载过程中，双筋墙中OOP位移的开始与沿边界区域纵向钢筋的抗压刚度（压缩屈服）的显着降低相符。特定高度（至少为壁高的60％）。根据这项研究的结果，设计了一个实验方案，并在面内循环载荷下对四个参数模型进行了实验测试。除上述参数外，还简要讨论了抗剪强度，边界条件和材料特性在整个壁厚上的偏心度对基准参数模型的OOP响应的影响。