Characterization and modelling of the nonlinear material behaviour of coated fabrics for architectural membrane structures II

由涂层织物制成的纺织膜结构目前在土木工程中是一种牢固建立的建筑形式，特别是用于大面积的无支撑屋顶。充分考虑材料刚度是有限元模型中膜预测建模的基础，从而可以计算膜和子结构中的机械载荷和位移，确保无损伤结构、安全和盈利。涂层织物薄膜在双轴拉伸试验中表现出各向异性和高度非线性的应力-应变行为。由于外部加载，材料的软化被观察到导致永久应变随着循环加载而增加，并在固定的最大载荷下表现出饱和行为。在确定膜结构的尺寸时，必须考虑由这种预处理产生的额外应变，然而，由于缺乏合适的模型，在当今的实践中并非如此。此外，非线性应力-应变行为目前由线性弹性公式近似，在预测应力和位移方面精度不足。这表明，在非线性材料响应的表征和建模方面存在一个基本的知识差距，计划在本研究项目中予以弥补。本项目的中心目标是发展概念，将纺织膜的载荷和结构相关非线性材料特性结合起来，用于膜结构的结构计算。本文的主要创新点和研究目标如下：开发了一种双轴拉伸试验程序，以确定纺织膜的结构和载荷相关的材料行为，该程序适应实际载荷情况，并考虑了外部载荷下的预应力和预处理过程。2. 发展了两种考虑纺织膜材料非线性特性的有限元计算方法：a.与载荷和结构相关的虚拟弹性常数和b.描述非线性非弹性材料特性的连续力学材料模型。3. 2.开发方法的验证。基于实验的大型施工试验，主要针对两种结构类型（平面结构和鞍形结构）进行了实际膜结构的位移和应力评估。4. 通过与非线性模型的对比分析，将采用虚拟弹性常数的方法推广到更多的结构形状（如高点膜和四点帆）。

Textile membrane structures made of coated fabrics are nowadays a firmly established constructive form in civil engineering, in particular for the unsupported roofing of large areas. The adequate incorporation of material stiffness forms the basis for a predictive modeling of the membrane in Finite Element models and thus for the calculation of mechanical load and displacement in the membrane and in the substructure, ensuring damage-free constructions, safety and profitability. Coated fabric membranes show an anisotropic and highly nonlinear stress-strain-behaviour in biaxial tension tests. As a result of external loading, softening of the material is observed leading to permanent strains which increase with cyclic loading and which show a saturating behaviour under fixed maximum load. The additional strains resulting from this preconditioning are essential to be considered when dimensioning a membrane structure, which, however, is not the case in nowadays practice due to a lack of suitable models. Moreover, the nonlinear stress-strain-behaviour is currently approximated by linear elastic formulations which yield an insufficient accuracy in the prediction of stresses and displacements. This shows that there is a fundamental knowledge gap with respect to the characterization and modeling of the nonlinear material response, which is planned to be closed in this research project. Central goal of this project is to develop concepts for the incorporation of load- and structure-dependent nonlinear material properties of textile membranes for the structural computation of membrane constructions. The main innovations and thus research goals are as follows: 1. Development of a procedure for biaxial tension tests to identify structure- and load-dependent material behaviour of textile membranes, which is adapted to the real load situation and which account for the prestress and preconditioning process under external loading. 2. Development of two methods for finite element calculations for the consideration of the nonlinear material properties of textile membranes base on: a. Load- and structure-dependent fictitious elastic constants and b. Continuum-mechanical material model for the description of the nonlinear inelastic material properties. 3. Validation of the methods developed in 2. based on experimental large-construction experiments mainly focusing on two structure types (plane and saddle-shaped form) for the assessment of displacements and stresses in real membrane structures. 4. Extension of the method using fictitious elastic constants to further structural shapes (e.g. high point membrane and 4-point sail) by comparative analysis with the nonlinear model.