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We present the results of the forced-vibration experiments performed at the large-scale prototype structure of EuroProteas founded on gravel-rubber mixture (GRM) layers acting as a means of Geotechnical Seismic Isolation (GSI). Three GRM with different rubber content per mixture weight (0%, 10%, and 30%) but the same mean grain size ratio were used as foundation soil. Each GRM-structure system was subjected to harmonic forces in a wide range of excitation frequencies and force amplitude. It was found that a 0.5 m thick GRM foundation soil layer with 30% rubber content can effectively isolate the structure. The strong effect of the rubber fraction was expressed in the detected period elongation and the dominating rocking component which leads to a more “rigid-body” response of the structure. Moreover, the developed base shear and base moment are significantly reduced regardless of the excitation frequency, while the increased damping of the system and the important energy dissipation demonstrate the effectiveness of the GRM foundation soil layer. Overall, the experimental results demonstrated that the use of GRM as a GSI system can be considered as a low-cost alternative seismic isolation technique.

Two structural configurations of the EuroProteas prototype structure, defining two test structures with different structural stiffness, were subjected to dynamic excitation to study the influence of soil-foundation-structure interaction effects on the recorded response. The first test structure was braced in all directions making a stiff structure frame based on soft ground. In contrast, we removed the bracing in the direction of loading in the second structure to significantly reduce its structural stiffness and the relative structure-to-soil stiffness ratio. Ambient noise measurements, free-vibration tests over a wide range of pull-out forces and forced-vibration experiments over a wide range of frequencies were included in the experimental series performed on both structures. The strong effects of the soil-foundation-structure interaction in the response of the stiff structure were expressed in the detected period elongation and the dominating rocking component which increased the radiation damping. The identified rocking stiffness was found to be frequency-dependent, in contrast to the lateral stiffness. On the contrary, the most significant proportion of the introduced energy was dissipated in the structural members of the second test structure, and the measured translation and rotation of the foundation were almost negligible.

Scour is the prevailing cause of bridge failure worldwide, leading not only to traffic disruption, but also to social and economic losses and even to casualties. Many vibration-based monitoring techniques have been proposed for identifying the scour location and extent, based on the evaluation of the changes of the bridge modal properties due to scour. This study describes the experimental and numerical research carried out to investigate the effects of scour on the dynamic properties of structures with shallow foundations. Although these are the most vulnerable ones, they have received less attention compared to structures founded on pile foundations. To fill some existing knowledge gaps, field experiments were carried out on EuroProteas, a structural prototype with shallow foundation that was subjected to increasing levels of scour. The changes of the dynamic properties of the system are evaluated by postprocessing the ambient vibration recordings and by developing various models of the soil–foundation–structural system with different descriptions of the soil–structure interaction problem. The study results shed light on the effects of scour on systems with shallow foundations and on the accuracy of alternative modelling approaches. They are presented here to inform the development and validation of vibration-based techniques and modelling strategies for bridge scour identification.