To accurately predict the dynamic response of a structure subjected to fluid induced loading, a thorough understanding of the dynamic properties (mass, stiffness, and damping) and associated interactions is required. Limited data are available to characterize dynamic fluid–structure interactions. Data are particularly limited for large-scale and flexible structural models. This article reports the results of the first free vibration tests of a dynamic large-scale laboratory highway bridge superstructure model. The dynamic response characteristics of the model were extracted and analyzed from free vibration tests under varying levels of water submersion and for different horizontal substructure flexibilities. The nature of the damping response was identified based on the empirically measured logarithmic decrements of the model’s free vibration displacement amplitudes, and a suitable equation of motion (EOM) was subsequently developed. Using the classical fourth-order Runge–Kutta method, the EOM was solved for the different test trials and the dynamic properties of the model were obtained through an optimization approach. The concept of added mass was introduced to explain the observed decrease in natural frequency with increasing levels of water submersion. Finally, added mass factor was computed for the case where the water level was even with the top of the bridge superstructure model. This study provides a suitable EOM needed for numerical simulations of this and similar models that study fluid–structure interaction and also provides a methodology for establishing the structural dynamic properties of generalized hydrodynamic analytical models.

为了准确预测承受流体诱导载荷的结构的动态响应，需要彻底了解动态特性（质量、刚度和阻尼）和相关的相互作用。可用于表征动态流固耦合的数据有限。大规模和灵活的结构模型的数据特别有限。本文报告了动态大型实验室公路桥梁上部结构模型的首次自由振动试验结果。模型的动力响应特性是从不同浸水水平和不同水平子结构柔性下的自由振动试验中提取和分析的。阻尼响应的性质是根据​​模型自由振动位移幅度的经验测量对数递减量确定的，随后开发了合适​​的运动方程 (EOM)。使用经典的四阶 Runge-Kutta 方法，求解不同测试试验的 EOM，并通过优化方法获得模型的动态特性。引入附加质量的概念是为了解释所观察到的固有频率随着水淹没水平的增加而降低。最后，在水位与桥梁上部结构模型顶部持平的情况下，计算了附加质量因子。