Nonlinear cyclic response of U-shaped flexural plates under quasi-static wind loading protocols: An experimental investigation

Abstract

U-shaped flexural plates (UFPs) made from rolled mild steel are widely used in seismic force-resisting systems (SFRSs) as replaceable energy-dissipating components. While their seismic performance is well documented, recent advancements in performance-based wind design (PBWD) require a deeper understanding of their nonlinear behavior under wind loads. Unlike earthquakes, wind loads contain a mean component and act over longer durations with numerous loading cycles, which can lead to low-cycle fatigue, degradation, and fracture. Despite their potential use as deformation-controlled elements in main wind force-resisting systems (MWFRSs), the nonlinear response of UFPs under wind loading has not been experimentally investigated. Accordingly, an experimental investigation of UFPs subjected to new quasi-static along-wind and across-wind loading protocols is presented here. These protocols were derived using rainflow counting applied to the response histories of UFPs in a prototype building subjected to loads obtained from wind tunnel tests. Thirty UFP specimens, with a constant bending diameter but varying thicknesses and widths, were tested under these protocols. A numerical model was developed in OpenSeesPy, and material model parameters were calibrated using the test results to support the PBWD of MWFRSs incorporating UFPs. The results demonstrate that UFPs maintain stable hysteretic behavior under 700-year MRI along-wind and across-wind loading protocols, sustaining more than 100 nonlinear excursions beyond a ductility level of 1.5. Under wind loading protocols corresponding to 3000-year MRI, stiffness degradation was observed. These findings support the use of UFPs as deformation-controlled elements in MWFRSs and provide a basis for their implementation within performance-based wind design frameworks.