The application of operational modal analysis using frequency domain decomposition revealed the operational behavior of a cantilever sign support structure in response to truck-induced wind gusts. The study identified the modes of vibration that contribute to the total deformation of the structure during service. The research involved experimentation of an on-site cantilever sign support structure under a controlled test regime of truck gusts. The study measured normal- and shear-strain deformations around the circumference of the post in proximity to the base-plate weld. The results indicated a multiple-degrees-of-freedom dynamic system with two equally contributing modes of vibration. The modes resembled torsional and flexural vibrations about the post. The resulting operational deflected shape had a distinctive beating vibration response due to the modal contributions. The truck fatigue loading provisions of the AASHTO supports specifications were overly conservative for the tested structure and truck type.
