Nonlinear Dynamic Response of Pretensioned Saddle-Shaped Membrane Structure Under Rainstorm Load: Numerical Simulation and Experimental Verification

Membrane roofs with saddle geometry are widely used in stadiums and public facilities that are highly exposed to rainfall. However, current design practice typically considers rainfall only in terms of seepage effects, drainage requirements, or static stability checks, while the influence of extreme rainfall on dynamic behavior and prestress loss has not been comprehensively quantified. In this study, the behavior of a restored engineering-scale saddle-shaped membrane roof under three representative rainfall intensities (50, 300, and 550 mm/h) is investigated through combined laboratory experiments (span L = 2.52 m) and numerical simulations, with particular emphasis on how supporting conditions and pretension levels affect vertical displacement, vibration propagation, and rainfall-induced edge-cable pretension loss. The findings are intended to reveal response mechanisms and trends, while quantitative extrapolation to full-size roofs should be conducted with scaling considerations. The numerical model is validated against the experimental results through comparisons of cable forces and vertical displacements. The results indicate that while the maximum vertical displacement induced by heavy rainfall is small (millimeter-level) and does not cause immediate failure, the rainfall event induces a significant permanent loss of pretension (a maximum observed relaxation of 10.4% in the edge cables for the tested specimen) in the edge cables. This relaxation degrades the structural stiffness, potentially compromising aerodynamic stability under subsequent wind events. Consequently, for the tested configuration, post-rainfall pretension inspection is recommended for events exceeding 300 mm/h, with retensioning suggested if significant tension loss is detected. This recommendation should be interpreted as an indicative engineering reference for the present specimen rather than a universal criterion for all saddle membrane roofs.