The primary structure developed from the original structure and bearing extra mechanical loading was introduced; and basing on it, the primary and secondary stress can be distinguished.%介绍了一次结构是在其原始结构解除不利约束的基础上得到的、能承受外加机械载荷的简化结构,并利用一次结构法识别了一次应力和二次应力.
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