Keywords: earthquake engineering, vulnerability assessment, bridges, dynamic analysis, fragility curves, Rhine bridge Emmerich.

One of the main causes for a high number of deaths during earthquakes is that rescue measures can often only be accomplished insufficiently and with a delay. Strategic important roads are impassable due to collapsed bridges, debris or fires so that rescue agencies cannot attain incident places. Hence there is a need to assess the seismic vulnerability of existing bridges in order to guarantee their functionality in case of an earthquake. The assessment procedures should consider the demands of the current standards and must be applicable in the engineering practise. Furthermore the forthcoming introduction of the Eurocode 8, Part 2 increased the need for reliable assessment procedures considerably.

In the present paper a general seismic vulnerability assessment system for bridges, developed within the framework of the ongoing research project "Seismic vulnerability assessment of bridges in Germany" funded by the German Federal Highway Research Institute, is introduced. The basis of the system is a hierarchical classification of bridges into different types. For each bridge type a vulnerability assessment procedure consisting of three different levels with an increasing expenditure of time is provided for the user of the system. The system developed is linked to a national database, which provides information for all strategic important bridges in Germany. The level of assessment can be selected depending on the scope and the accuracy required.

At investigation level I, a fast and relatively inexpensive assessment based on information taken from construction plans, site characteristics and bridge inspection results is performed. Furthermore the bridge importance for traffic and rescue measures is taken into account. The evaluation results of the recorded information are used to detect the structural deficiencies and to determine the fragility curves, which quantify the likelihood of the occurrence of certain damage states. At investigation level II, a linear response spectrum analysis based on a two dimensional finite element model is carried out to determine the damage indicators. The generation of the numerical model is executed by the system on the basis of the geometry and material input parameters. The vulnerability function of the bridge is obtained by running the investigation level II calculation for different return periods. At investigation level III a significantly more precise time history analysis with a detailed three dimensional finite element model is carried out to determine the damage indicators. The model includes geometric and physical nonlinearities as well as the soil-structure interaction effects. The vulnerability function is calculated by using artificially generated time-history accelerograms for different return periods. Measurement of the eigenfrequencies is carried out to calibrate the numerical model. A level III investigation is only required when the results at the first two investigation levels identify a critical bridge behaviour under seismic loading.

The practical use of the developed system is illustrated for the famous suspension bridge Emmerich located in North Rhine-Westfalia in Germany. The bridge Emmerich is the longest suspension bridge in Germany and connects the town Emmerich on the eastern side of the Rhine to Kleve on the western side. The seismic hazard curve for the bridge location was obtained from a probabilistic earthquake hazard assessment (PSHA) based on the earthquake catalogue for Germany taking into account the local underground conditions. The results of the investigation level I assessment with respect to the specific characteristics of suspension bridges is discussed. Furthermore the generation of the two and three dimensional finite element models for the investigations in investigation levels II and III are presented. A special focus is set on the form finding process for the main cables of the suspension construction. Both models were calibrated by the results of in-situ measurements of the bridge. Because of the span width of the bridge the non-linear analysis in investigation level III was carried out with uncorrelated base excitations at the pylon foundations.

Finally the vulnerability of the suspension bridge Emmerich is discussed on the basis of the results in the different investigation levels. The deficiencies of the bridge are shown and general conclusions for the seismic vulnerability of suspension bridges are derived for engineering practise.

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