One important and challenging aspect of the design process for tensile membrane structures is the determination of biaxial material stiffness parameters. Coated textiles that are used as architectural fabrics display highly nonlinear and anisotropic stress-strain behaviour under biaxial tensile stresses. Nevertheless, in state-of-the-art structural analyses, the behaviour of these coated textiles is often simplified to a linear-elastic plane stress relationship, where the elastic constants are "tensile stiffness" and "Poisson's ratio." The elastic constants must be determined for each material using biaxial tensile tests. Several different biaxial test procedures to determine the elastic constants exist worldwide, and these procedures yield various sets of elastic constants with a wide spectrum of stiffness parameters. At the same time, design engineers have no guidelines to assess which set of parameters is appropriate for a specific design situation. This paper compares two different methods of determining stiffness parameters using theoretical and experimental analyses. The variation in structural analysis results due to stiffness parameters that were determined using different techniques is demonstrated using three types of PES/PVC materials from two material producers. Furthermore, this paper provides guidance regarding the manner of evaluation of sets of elastic constants and the modification of the evaluation of experimental biaxial tests, if required. Information is also provided concerning the applicability of the investigated procedures.Tensile or membrane structures are often incorporated into modern infrastructure applications as a means to achieve elegant structural forms with low self-weight. Examples can be found in bridges, long-span roofs and temporary or special structures. Due to their low self-weight and limited redundancy, these structural forms can present numerous unique design or construction challenges. Their structural response must be fully understood under the temporary configurations occurring during construction. The unique mechanical properties of non-traditional materials frequently used in tensile or membrane structures can also present specific challenges or constraints.This issue of Structural Engineering International contains a special series of six scientific papers to highlight some of the recent developments in the field of Tensile and Membrane Structures.The first two papers in this series examine different aspects of the design and performance of structures constructed from light, fabric membranes. Uhleman et al. present a study that contrasts different standardized protocols used to arrive at design parameters for the modeling of material properties of textile fabrics. A paper by Milosevic examines the influence of concentrated loading on the deformation characteristics of a membrane structure.Beam string structures, which have seen increased adoption for use as long-span roof systems, are notable because their active change in geometry during construction needs to be co...

Woven coated fabrics commonly used for tensile membrane structures are PVC‐coated polyester fabrics and PTFE‐coated glass‐fibre fabrics. Regarding the stiffness of these materials, membrane structure experts frequently point out that glass/PTFE fabrics are “stiffer” than PES/PVC fabrics. However, this statement cannot be verified by existing literature, although numerous publications deal with the stress‐strain behaviour of coated woven fabrics. Available stress‐strain test data are almost impossible to compare, mainly because published stress‐strain data for glass/PTFE refer to materials with higher strengths than the published test data for PES/PVC materials. The aim of the present paper is to compare the stiffness properties of PES/PVC and glass/PTFE fabrics with identical tensile strength properties by means of theoretical investigations and uniaxial tensile tests. The results demonstrate that glass‐fibre fabric indeed exhibits a higher tensile stiffness than comparable polyester fabric for typical working stress ranges between the prestress level and the maximum design strength. However, for lower stress ranges up to approximately three‐quarters of the design strength, the tensile stiffness of glass‐fibre fabrics is identical with or even lower than that of comparable polyester fabric. The transverse strain is considerably higher for the glass‐fibre fabric throughout.