Influence of initial Deflections on Coupled Buckling Strength of Unstiffened Square Box Section Columns

Although it is well known that initial deflections have a significant influence on coupled buckling strength, their quantitative influence is not clear. In this paper, a series of nonlinear finite element analyses to reveal the quantitative influence of initial deflections on coupled buckling strength are conducted with MSC.Marc. There are nine kinds of combinations about the size of local and overall initial deflections including 1/75, 1/150, 1/450 of the plate width and 1/500, 1/1000, 1/3000 of the column length. In addition, the width-thickness ratio and slenderness ratio parameters are also varied in the parametrical study. Both ranges of slenderness and the widththickness ratio parameters are from 0.1 to 2.1. As a result, the initial deflection influence coefficient is proposed to describe the quantitative influence of local and overall initial deflections on coupled buckling strength. The numerical results reveal that the coefficient decreases with the increase of initial deflections. The sensitivity of the strength to initial deflections depends on both width-thickness and slenderness ratio parameters. The maximum decrease of 21.4% on load-bearing capacity caused by local initial deflection appears when width-thickness and slenderness ratio parameters equal to 1.2 and 2.1, respectively. Column strength is quite sensitive to overall initial deflection at the slenderness ratio parameter equal to 1.4. The maximum decrease in load-bearing capacity reaches 18.2%.

尽管学界已公认初始挠度(initial deflections)对耦合屈曲强度(coupled buckling strength)具有显著影响，但其量化影响机制仍未明确。本文采用MSC.Marc软件开展了一系列非线性有限元分析，以揭示初始挠度对耦合屈曲强度的量化影响。针对局部与整体初始挠度的幅值，本文设置了9种组合工况：局部初始挠度分别取板宽的1/75、1/150、1/450，整体初始挠度分别取柱长的1/500、1/1000、1/3000，共形成9种组合形式。此外，本次参数化研究还对宽厚比(width-thickness ratio)与长细比(slenderness ratio)参数进行了变量设置，两类参数的取值范围均为0.1至2.1。基于上述数值分析结果，本文提出了初始挠度影响系数，用于量化表征局部与整体初始挠度对耦合屈曲强度的影响。数值分析结果表明，该系数随初始挠度幅值的增大呈下降趋势。结构强度对初始挠度的敏感程度同时受宽厚比与长细比参数的共同影响。当宽厚比参数取1.2、长细比参数取2.1时，局部初始挠度可导致结构承载力最大降低21.4%。当长细比参数取1.4时，柱体强度对整体初始挠度较为敏感，此时承载力最大降幅可达18.2%。