摘要
单层球面网壳,由于其壳面整体较薄,受载时其构件以受压为主,非线性(几何非线性、材料非线性)的影响十分明显,并且,网壳结构为缺陷敏感结构,对其进行详细的缺陷稳定性研究具有重要的理论与工程意义。
在总结改进随机缺陷法的优、缺点基础上,在改进随机缺陷法的程序中嵌入智能程序,自动控制随机缺陷法的计算样本数,结束了靠经验选取样本数的历史,为大规模参数化分析奠定基础,也使随机缺陷法能更好地应用于工程实际。
在上述基础上对凯威特型单层球面网壳进行大规模参数化分析(共进行了不少于82000次的网壳结构非线全过程分析),系统研究了具有随机缺陷的凯威特型单层球面网壳的稳定性能,归纳了网壳跨度、矢跨比、截面尺寸、缺陷最大值、弹性与弹塑性对凯威特型单层球面网壳设计临界荷载的影响。此外,还对随机缺陷法计算样本数进行了研究,随机缺陷法的计算样本数比较恒定,一般在55-60之间。
基于大规模参数化计算,详细研究了缺陷影响系数与塑性影响系数,当缺陷最大值为L/1000时,缺陷影响系数LP可取0.45,当缺陷最大值为L/500时,L P可取0.35,当缺陷最大值为L/300时, LP可取0.25。结构无论有无缺陷,塑性影响系数K P约为65%-70%,即考虑材料非线性约使网壳极限承载力下降30%-35%。
本文还对一致缺陷模态法的可靠性进行研究。一致缺陷模态法计算结构的临界荷载的概率可靠度在90%以上的弹性分析时占80%~90%的比例,而弹塑性分析时约占75%的比例,因此,对于许多结构,特别是比较重要、复杂或是缺陷敏感结构,采用一致缺陷模态法作为其整体稳定性验算的唯一方法时需谨慎。
The effect of nonlinear (geometric nonlinearity,material nonlinearity) of Kiewitt single layer latticed spherical shell is very obvious as a result of the global thin-shell surface and compression-mainly. The single layer latticed spherical shell belongs to the imperfection sensitive structure. The study of stability analysis of Kiewitt single layer latticed spherical shell with stochastic imperfections has many important theoretical and practical values.
A intelligent program was imbedded into the improved calculation procedure of the advanced stochastic imperfections method on the conclusion of the advantages and disadvantages of the advanced stochastic imperfections method. The intelligent program can automatically control the calculation numbers of advanced stochastic imperfections method and end the history of the calculation number of samples selected by experience. The intelligent controlling procedure establishes the foundation of large-scale parametrization analysis.It also makes the advanced stochastic imperfections method better to be applied.
A systematical stability analysis of Kiewitt single layer latticed spherical shell with stochastic imperfections was carried out to study the stability behavior on the base of large-scale parametrization analysis (the times of non-linear analysis was no less than 82000). The influence of the span, the rise-to-span ratios, the sectional dimensions, the maximum of initial imperfections, the elasticity and plasticity to critical design load of Kiewitt single layer latticed spherical shell were also studied. The calculation numbers of the stochastic imperfections method were detailly studied. The results show that the calculation number of the stochastic imperfections method is stability, generally from 55 to 60.
The imperfect influence coefficient and the plastic influence coefficient were detail studied which based on large-scale parametrization analysis. The imperfect influence coefficient can be taken 0.45 desirable when the maximum initial imperfections is L/1000 and 0.35 desirable when the maximum initial imperfections is L/500 and 0.25 desirable when the maximum initial imperfections is L/300. No matter the structure have initial imperfection, the plastic influence coefficient can be taken 65%-70% which means the critical load of Kiewitt single layer latticed spherical shell may nearly drop by 30%-35% if material non-linear was considerd.
The probabilistic reliability of the consistent imperfection mode method was also studied. The result showed that the proportion of the reliability over 90% is 80%~90% when elastic analysis was carried out with consistent imperfection mode method and about 75% when elastic-plastic analysis. Therefore, the consistent imperfection mode method should be adopted cautiously.
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