In today's structural design practice for textile structures, still one of the most challenging aspects is the determination of material stiffness parameters. The only constitutive law used in practice describes orthotropic linear-elastic stress-strain relations in the two principal directions. The elastic constants are "tensile modulus" and "Poisson's ratio". In contrast, the actual stiffness behaviour of architectural textiles is nonlinear and nonelastic. Moreover, the potential high

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... y of textiles is often not sufficiently covered by the test and evaluation methods available. This paper presents principles for refined biaxial test procedures that fit to the requirements of structural fabrics. As a result, sets of elastic constants for design purposes can be determined which ensure a very good correlation between measured and calculated strain on a specific stress level for all common PVC-coated polyester fabrics and PTFE-coated glass fibre fabrics. Furthermore, the refined method enables to model the very high transverse strains which are observed especially for glass-PTFE fabrics.