故宫中和殿某中金檩断裂分析

勘查发现,故宫中和殿明间某中金檩在与上部爬梁相交位置出现局部断裂,造成下部中金枋产生较大挠度.为探明该中金檩产生断裂的原因,采取理论计算与数值模拟相结合的方法,对中金檩、中金枋体系进行了分析.基于榫卯连接边界条件的特征,分别考虑中金檩与中金枋叠合、中金檩与中金枋分离、中金檩完全断裂等三种工况,建立了中金檩-枋体系的受力模型,进行了静力分析,获得了中金檩、中金枋的变形及内力分布特征,讨论了中金檩断裂破坏的影响因素.结果表明:由于中金檩在爬梁作用位置截面削弱,造成中金檩自身拉、压、弯承载力不足,从而导致中金檩产生断裂；中金檩与中金枋分离条件下,中金檩断裂造成的中金枋内力增加,且比檩枋叠合条件更明显；中金檩完全断裂后,将造成中金枋内力及变形剧增,威胁中金枋安全.因此,对中金檩采取及时有效的加固措施极其重要.研究结果将为中金枋采取加固措施提供理论参考.

Analysis of rupture of a mid inner purlin in Zhonghe Palace in the Forbidden City

It was found that during a survey that part of a mid inner purlin in Zhonghe Palace in the Forbidden City ruptured at the intersection between the purlin and the beam above it, which led to large deflection of the purlin and the tie beam under it. By theoretical calculation and finite element simulation methods, the cause of the purlin rupture was studied. Based on the boundary characteristics of the tenonmortise connection, analytical models of the purlin and tiebeam were built. Situations where the purlin superposes on the tie beam, detaches from the tie beam, and becomes completely ruptured were studied. By static analysis, deflection and inner force distributions of the purlin and the tie beam were obtained, and factors causing the rupture of the purlin were discussed. The results showed that weakening of the bearing section of the purlin at the intersection location caused insufficient bearing capacity of the purlin, which leads to its rupture. Compared to the case where the purlin superposes on the tie beam, the case where the purlin detaches from the tie beam makes the rupture more severe. When the purlin completely ruptures, the upper loads transferred to the tie beam increases sharply, which threatens the safety of the tie beam. Thus it is important to strengthen the purlin in time.