Instabilities in membrane structures under extreme conditions

The complex instabilities of innovative structural membranes are investigated for disclosing their vulnerability and design strategies to mitigate the critical conditions. The research focuses on two different loading conditions, each one leading to a specific mechanical instability of the membranes: wrinkling under quasi-static conditions and flutter instability due to dynamic conditions of wind flow. In the first part of the thesis, the wrinkling analysis is addressed by removing the hypothesis of prevented lateral contraction, usually considered in literature. A novel approach is introduced with reference to a quasi-rectangular parallelogram and trapezoid, obtained as perturbations of the rectangular shape by a small angle. It is shown that wrinkling for both quasi-rectangular geometries can occur even without preventing lateral contraction when the perturbation angle is greater than a minimum threshold depending on the aspect ratio and found to be smaller for the trapezoid than for the parallelogram. Furthermore, by assuming a neo-Hookean hyperelastic response, the self-restabilization of the planar state is disclosed at increasing deformation, in analogy to previous observations under the classical setting (namely, a rectangular membrane with lateral contraction prevented). A robust understanding of this phenomenon is provided by deriving approximate in-plane solutions and validating them against finite element method (FEM) simulations. As a final result of the analysis, the critical (wrinkling and restabilization) surface is disclosed within the deformation -- perturbation angle -- aspect ratio space. The flutter dynamics of tensile panels induced by wind loading conditions is investigated in the second part of the thesis by means of Fluid-Structure Interaction (FSI) analyses, enhanced by vortex-induced vibration (VIV) simulations. The study elucidates the relationship between tension thresholds and dynamic instability, highlighting the significance of lock-in effects and vortex-induced phenomena. The behavior under various geometries and constitutive models can be accurately predicted through the proposed approach, which can be used as an effective simulation tool for facilitating the design of safer and more resilient tensile structures. The implications of this research extend to practical applications within the industry. The writer's secondment at Tensys Ltd. ensured that the findings are directly applicable to real-world scenarios, enhancing the safety, aesthetics, and efficiency of structural membrane designs. Future work will focus on implementing new constitutive models for ETFE materials under high-speed wind and exploring large deformation solutions to further understand membrane restabilization. By employing meticulous research methodologies and interdisciplinary synthesis, this investigation contributes to the advancement of structural engineering knowledge, offering valuable insights into mitigating instabilities in innovative structural membranes.