At the first part of this paper, topics concerning current state-of-the-art techniques for the seismic analysis of major river-crossing highway bridges are introduced in conjunction with soil-foundation-bridge interactions. These include earthquake accelerograms, multiple-support excitations and analyses of soil-pile-bridge interactions by Winkler-type spring model, boundary element model and finite element model. From the discussion, it is concluded that a full-scale three dimensional finite element model should be examined in order to develop a more effective simplified method which can be used in engineering practice. An existing truss-arch highway bridge in Southern Illinois is selected for the case study. The structure is located on deep alluvial soil deposits and the piers for the main span are on floating caissons and the piers of the approaches are on friction pile foundations. A three dimensional model of the bridge, along with its approaches, is developed. The preliminary results on the dynamic characteristics of the bridge are reported here.
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