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Seismic Safety of Existing Bridges (AGB2003/014)

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Vehicle design and manufacturing (VDM)
Infrastructure (INF)
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Background & Policy context

The new Swiss standard SIA 261 prescribes seismic design actions significantly larger than in the past. Therefore, 90% of the Swiss bridges isn’t properly designed or isn’t designed at all to withstand an earthquake. Such bridges are characterized by an unknown seismic performance and their vulnerability is also mostly unknown.

To overcome this problem ASTRA developed a two stages assessment procedure for existing girder bridges. In the first stage the all bridges are assessed and the ones showing excessive vulnerability identified. Such bridges are analysed in depth during the second stage. To accomplish this task it is recommended to make use of displacement-based procedures.


Goal of the research project is the numerical and experimental analysis of existing girder bridges. The analysis aims in the development of displacement based assessment procedures for this kind of bridges. Such assessment procedures are particularly suited for regions of moderate seismicity. In many cases they allow a more favourable assessment of the available seismic safety. Hence, it is expected that the seismic safety of the majority of Swiss girder bridges is suitable even without retrofitting.


The research project starts with a literature review. Subsequently, the seismic behaviour of girder bridges is investigated based on numerical simulations and experiments. Practical design rules are derived ultimately based on theoretical studies.


The research project resulted in the development of the bases needed for the displacement-based assessment of existing girder bridges. The project results are made up of four parts: 

1) Numerical investigation of the seismic behaviour of typical girder bridges. 

2) Experimental investigation of the displacement capacity of conventional concrete bridge piers. 

3) Development of guidelines, based on experimental and numerical evidence, to perform 
displacement-based assessment of existing girder bridges. 

4) Development of guidelines to perform a realistic numerical simulation of girder bridges 
under seismic action.

Innovation aspects

It is intended to formulate the fundamentals of deformation based review of existing girder bridges so that they can be used directly in practice.


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