Direct Displacement-Based Seismic Assessment of Multi-Span Simply Supported Deck Bridges

Abstract eng:
Traditional seismic assessment is based on a simple comparison of estimated base shear capacity and base shear demand specified by a seismic code. The required code base shear is found by reducing the elastic base shear force corresponding to the elastic stiffness of the structure, by a code-specified force-reduction or behaviour factor. The problems with this approach are that no assessment is made of the actual collapse mechanism, inelastic deformed shape and ductility demand of the structure. In recognition of the limitations of forcebased design and assessment methods, several researchers have started proposing displacement-based approaches for earthquake engineering evaluation and design, with the aim of providing improved reliability in the engineering process by more directly relating computed response and expected structural performance. The need for accurate seismic assessment methods is particularly important for bridges, due to the crucial role that some bridges (especially highway bridges) have after an earthquake, for allowing the civil protection interventions and first aid organizations. In Italy, many of these “strategic” bridges have been built without antiseismic criteria and, therefore, they need to be assessed against seismic risk. In this extent, the development of an assessment procedure which gives reliable results and, at the same time, is sufficiently simple to be applied on a large population of bridges in a short time is very useful. In this paper a Direct Displacement-Based Seismic Assessment (DDBA) procedure satisfying the aforesaid requirements is proposed. In the paper, the proposed DDBA procedure is applied to a number of bridge configurations derived from a 4-span reinforced concrete simply-supported deck bridge of the A16 Italian highway. Some analyses are also repeated following the traditional force-based seismic assessment approach. Finally, the predictions of the proposed DDBA procedure are compared to the results of nonlinear time history analyses.

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