Failure analysis of cast aluminum A356-T6 light pole bases following Catastrophic Hurricane Exposure: Microstructural, Mechanical, and Fractographic investigations

Multiple aluminum light poles in Florida failed during recent hurricanes at wind speeds below design specifications, raising concerns about structural integrity and manufacturing quality. This study investigates the failure of cast A356-T6 aluminum alloy bases through combined metallurgical analysis and finite element modeling. Computed Tomography (CT) and metallography revealed critical porosity levels (up to ~8.2%) exceeding ASTM acceptance thresholds, along with microstructural variability near bolt holes. Local hardness and tensile testing indicated reduced yield strength, consistent with casting defects and installation-induced pre-strain, while fracture morphology confirmed monotonic overload rather than fatigue. A full-scale finite element model of the Lake Jessup Bridge base assembly was developed to evaluate stress distribution under design-level and hurricane-level wind loading while incorporating measured material properties and installation irregularities. Simulations showed that when porosity-reduced strength was combined with geometric stress risers and uneven leveling-nut preload, localized stresses exceeded the experimentally measured yield strength (~116 MPa) even under wind speeds below design thresholds. This study is the first to integrate CT-quantified porosity, field installation audits, tensile testing, and wind-driven structural modeling to explain premature hurricane-induced failures of cast aluminum pole bases. The findings demonstrate that premature failures resulted from the synergistic interaction of casting defects, geometric vulnerability, and installation-induced overloads rather than a single governing mechanism. Recommendations include stricter casting quality control, torque-limiting installation protocols, and minor design modifications aimed at reducing stress concentrations and improving reliability of aluminum infrastructure in hurricane-prone regions.