The Theory for Unstable Structures and It's Applications to the Shape-Finding Problems

膜结构、索结构和带机构的桁架结构因其自重小、施工方便等优点，越来越多地被应用于空间结构。另一方面，它们的不稳定性带来了一些新的问题。出现了大位移、预拉伸、找形等问题。在这项研究中，我们发展了基于“不稳定结构理论”的不稳定结构找形分析方法。然后进行了实验测试，验证了该方法的正确性。我们在这一年进行的研究如下：1.方法的应用：将本文提出的失稳连杆结构找形方法应用于实际建造的大型气动结构充气过程的分析。二维链模型的实验研究：为了验证分析方法的正确性，进行了二维链模型的实验研究。实验中，液体甘油被有效地用于实现“准静态”。计算结果与分析结果吻合较好。X-y-z测量系统：利用已研制的x-y-z测量系统对单层网架穹顶和三维连杆模型进行了测量。结果表明，该系统适用于不稳定结构稳定过程中的大位移测量。不稳定拱的实验制作：不稳定拱是受压结构，是一般认为是张拉结构的不稳定结构的特例。为了更好地把握失稳结构，我们在实验中制作了失稳拱架，并进行了搭建。

Membrane, cable structures and truss structures with mechanism have been coming more adoptable for spatial structures because of their small dead loads and convenience at the constructive stage. On the other hand, their property of unstability bring about several new types of problems. The problems concerning large displacements, pre-tension and shape-finding are coming about. In the study, we developed the analytical method for shape-finding of unstable structures based on "the theory of unstable structures". Then we made some experimental tests to certify the propriety of the method. The studies which we have carried out during this year are as follows.1. The application of the developed method : We applied our shape-finding method developed for unstable link structures to the analysis of the inflating process of a large pneumatic structure already constructed in practice.2. The experimental studies of two dimensional link models : For the purpose of the confirmation of propriety of the analytical method, the experimental studies of two dimensional link models were carried out. The liquid glycerin were effectively used to realize " the quasi-static states " in the experiments. The results agreed well with those of the analyses.3. The x-y-z measuring sustem : A single layer space frame dome and a three dimensional link model were measured with the x-y-z measuring system which have been already developed. The results proved the applicability of the system to the measurement of large displacements which occur during the stabilizing processes of unstable structures.4. Experimental production of an unstable arch : The unstable arch is a compressive structure and is the special case for the unstable structures which are generally considered to be the tensile structures. For the good grasp about the unstable strucbtures, we produced an unstable arch experimentally and set it up.