High-Temperature Tensile Strength and Constitutive Models for PVC-Coated Fabrics with Welded Seams

Welded seams represent weak parts in air-supported membrane structures when subjected to fire. However, existing research primarily focused on the mechanical properties of welded seams at temperatures below 70°C, without investigations about constitutive models. In this paper, the high-temperature tensile strength and constitutive model of PVC-coated fabrics with three different types of welded seams were investigated, extending the temperature range to 120°C to addresses these gaps. Three failure modes were proposed based on the damage characterization: base membrane fracture, base membrane pull-out, and coating slippage and stripping. These failure modes were found to be significantly influenced by both temperature and welding type. The results demonstrated that welded seams exhibit greater sensitivity to high temperatures compared to base membranes without welded seams. The fracture strength exhibits a linear decline as the temperature rises. When the temperature increases from 25°C to 70°C, the strength approximately halves. As the temperature rises to 120°C, the welding seams nearly lose their load-bearing capacity. The elastic modulus decreases in a quadratic manner as the temperature rises. Further, piece-wise constitutive models of each welded seam were proposed by analyzing the stress–strain curves. Second, a critical safe working temperature range of 45–80°C was established as a structural fire failure criterion. Finally, a theoretical and an empirical model were proposed to predict tensile strength and elastic modulus at high temperatures, which can quickly and accurately estimate the high-temperature performance of other PVC-coated fabrics with welded seams without conducting expensive and complicated tests. The study provides an important basis for researching the air-supported membrane structure fire response.