Elastic constants of architectural fabrics for design purposes

One important and challenging aspect of structural fabric analysis is the determination of stiffness parameters that sufficiently model the stress-strain behaviour for biaxial stress states. The particular difficulty is that coated woven fabrics exhibit very complex stiffness behaviour. Current membrane structure design practice is nevertheless based on a simplified orthotropic linear-elastic plane stress relationship, where the elastic constants are „tensile modulus“ and "Poisson's ratio". The elastic constants must be determined for each material using biaxial tensile tests. In this work, principles are developed for the determination of elastic constants as input parameters for the design of fabric structures. The objective is for the elastic constants to closely approximate the relevant fabric stress-strain response for any fabric structure and the most common types of coated woven fabric: PVC coated polyester fabrics and PTFE coated glass fibre fabrics. Principles for refined biaxial test procedures are therefore derived together with a refined evaluation procedure. The principles are closely linked to the requirements of the structural design process. The aim is to determine elastic constants that ensure consistent analysis results and safe and simultaneously economical verification. Example applications of the refined procedures illustrate that deviations between the measured and calculated strain on a specific evaluation stress level are low throughout. This is striking evidence that linear elastic constitutive law can be very useful in approximating the stress-strain behaviour of all common types of coated woven fabric.