Assessment of Hydrodynamic Properties from Free-Vibration Response of a Prestressed Girder Bridge Model

Researchers at Oregon State University's Hinsdale Wave Research Laboratory tested a scaled prestressed girder bridge model to quantify the hydrodynamic forces, including added mass and drag, that act on bridge superstructures during storm surge and tsunami inundation. Using snap-release free-vibration tests under dry and submerged conditions, the study found that added mass stays roughly constant across excitation levels and depends mainly on submerged geometry, while drag coefficients vary with oscillation amplitude due to nonlinear flow effects. The results show that inertial forces dominate during rapid loading events and that partial submergence can dampen the response through water sloshing between girders, providing calibration data for numerical models used to assess coastal bridge vulnerability.