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Boundary conditions of a structure affect its response to dynamic excitations. In most highway bridge designs, the dynamic soil-structure interaction is not considered, with an underlying assumption that bridge piers have fixed-ends. Foundation flexibility, and more importantly radiation damping from the foundation, whether it is a shallow or deep foundation, can significantly influence the response of substructure/superstructure system. This may lead to deviations of the actual response compared to the design assumptions, depending on soil properties and geometrical and structural characteristics of the bridge. Low-magnitude shaking can be used as the means of evaluation of actual dynamic characteristics of a bridge. Moreover, numerical simulations of the same bridge with the same low-magnitude shaking load on the bridge can be used to model the dynamic response of the bridge, with the consideration of the dynamic soils structure interaction. In this paper, a comparison between the actual response of a bridge in Hamilton Township, New Jersey, and results from numerical simulations is presented. The shaking of the bridge was done using T-Rex, a large mobile shaker from NHERI Experimental Facility at University of Texas at Austin. The test setup, and results from both numerical simulations and field-testing are presented and discussed. Experimental results confirm that the FEM model developed is adequate to infer dynamic characteristics through the eigenmode analysis.
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Assessing the Significance of Dynamic Soil-Structure Interaction Using Large-Amplitude Mobile Shakers
To accurately describe the dynamic characteristics of bridges, it is important in some instances to take into consideration the flexibility and damping of the soil-foundation system. The ability to evaluate those properties in the field can serve as both a check for the design assumptions, and as assistance in the design of bridges with similar superstructure/substructure loading and soil conditions in the future. The goal of the presented study is to demonstrate the use of large-amplitude shaking as an effective tool in measuring actual response/behavior of bridges, and developing better understanding of the dynamic response of bridge systems. For that purpose, a large-amplitude shaking of a bridge in Hamilton Township, New Jersey, was carried out. The T-Rex, a mobile shaker from the Natural Hazards Engineering Research Infrastructure (NHERI) experimental facility at the University of Texas, Austin was employed to shake the bridge. A large number of sensors, geophones and accelerometers, were installed at various locations on the bridge deck, pier cap, and on the adjacent ground to capture the dynamic response of the bridge system. Furthermore, the results from field testing were used to calibrate a 3D finite element model of the bridge. The model was used to conduct a comparative analysis of the bridge response for the assumption of the bridge with fixed foundation conditions, and the bridge with the consideration of dynamic soil-structure interaction (DSSI) effects. The comparison with the field testing results demonstrate that the fixed foundation assumption model does not fully capture the behavior of the bridge, as opposed to the model with DSSI considerations.
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- Award ID(s):
- 1650170
- PAR ID:
- 10080014
- Date Published:
- Journal Name:
- 2019 Geo Congress, ASCE
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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