An 80 years old arch bridge on the Aare River connecting the Swiss cantons Solothurn and Aargau suffers from some cracking of its main girders presumably caused by vibrations due to relatively dense heavy traffic. It is planned to rehabilitate the bridge in 1994 by means of structural reinforcement measures. As a first step of a synergetic approach an experimental modal analysis was performed in June 1992. A randomly driven servohydraulic actuator producing a maximum vertical force of 5 kN and three-dimensional acceleration measurements in 144 selected points were used to obtain the frequency response functions and subsequently the dynamic characteristics of the bridge i.e. its dominant eigenfrequencies, corresponding mode shapes and damping ratios. These results were used as a reference base for a finite element analysis of the bridge using MSC/NASTRAN. An FE model consisting of 304 plate and solid elements was able to reliably reproduce the linear elastic behavior of the structure in its first seven natural modes. The agreement between the FE model and experimental modal data could even be improved by means of the sensitivity, correlation and optimization algorithms contained in the LMS Link Software. The updated and validated FE model was then used for various parameter studies in order to evaluate the optimum structural modification solution and also for the evaluation of specific design load cases.
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