AbstractA fixed base is generally assumed in various dynamic response analyses and the design of bridges. However, soil–foundation flexibility and energy absorption and radiation by the soil system can alter the response of bridges to dynamic loads. This interaction between the structure, foundation, and soil, which in some cases may even change the dynamic load transmitted through the ground, is, in general, referred to as dynamic soil–structure interaction (DSSI). DSSI can either have detrimental or beneficial effects on a bridge response, particularly forces and displacements. These effects depend on several factors such as the rigidity ratio (ratio of the stiffness of the structure to the same of the soil–foundation system), slenderness ratio (height of the structure to the base width ratio), the foundation type, and the mass of the structure relative to the mass of the engaged soil–foundation system. In this paper, the dynamic characteristics of an actual bridge are inferred via an experimental study and numerical simulations. The research concentrated on the evaluation of the significance of DSSI effects under operational live load levels. The bridge was shaken using T-Rex, a large-amplitude mobile shaker from the National Hazards Engineering Research Infrastructure (NHERI) facilities. Two finite-element models were created to assess the DSSI effects on the dynamic response of the bridge. One model included elements that incorporate the DSSI effects, while the other had fixed-base boundary conditions. The response from the DSSI FEM model matched the field results better than that from the fixed-base model, in terms of the peak response amplitudes and identified natural frequencies and modes. In addition, the model incorporating the DSSI effects led to a reduction in stress levels in various bridge components, compared with that of the fixed-base model. The results of this study are applicable to bridges with similar features and site conditions.

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