Aerodynamic Characterization of Porous Bluff Bodies: A Wind Tunnel Investigation of Truss Bridges

Abstract

Bridges are highly susceptible to aerodynamic and hydraulic loading due to their proximity to water bodies and exposure to extreme weather events. With climate change driving an increase in the frequency and intensity of such events, understanding the influence of structural porosity on the aerodynamic behavior of truss bridges has become increasingly important. This study experimentally investigates the aerodynamic drag characteristics of truss bridges in a wind tunnel, with the aim of characterizing the relationship between drag coefficient Cd, Reynolds number Re, and structural porosity 𝛽 in the subcritical flow regime (Re = 10^4 - 10^5). Four bridge configurations were developed based on the Picassent truss bridge, which was damaged during the 2024 Valencia flood in Spain. These configurations represent common truss topologies: Pratt (𝛽 = 75.85%), Warren without Verticals (𝛽 = 75.75%), Warren with Verticals (𝛽 = 69.99%), and a partially covered Warren simulating debris accumulation (𝛽 = 34.98%). An inverse relationship between drag coefficient and porosity was observed, with drag decreasing as porosity increases, consistent with existing literature. Additionally, the effective Reynolds number, which incorporates structural porosity, was found to provide a more physically meaningful scaling parameter for comparing porous structures of varying porosity. These results highlight the importance of incorporating structural porosity into the aerodynamic design of large truss bridge structures. As this study was conducted at low wind speeds (6-14 m/s), it serves as a preliminary investigation, with the bridge models acting as prototypes for future testing in the High Reynolds Number Test Facility (HRTF) to explore behavior in the supercritical flow regime.