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This paper deals with full scale forced modal testing performed on an 80 year old arch bridge over the Aare river in Switzerland. This bridge with a span of 72 m suffers from cracks of its main girders caused by vibration from heavy traffic. The dynamic behaviour of the bridge was determined experimentally with a servo-hydraulic exciter using a band-limited random burst force signal. The responses (accelerations in three orthogonal directions) were measured at 144 points distributed over the bridge. The result of modal testing in the form of a "reference modal/mathematical model" was applied to update an FE-model of the bridge. This updated FE-model of the bridge was used in various parameter studies in order to develop an optimum structural modification of the bridge and immunity to traffic excitation via relocation of structure resonances. In this paper it is shown that full-scaled force modal test is a successful way of obtaining the modal model of large civil engineering structures such as a bridge resulting in a description and understanding of the essential bridge dynamic behaviour. In addition, this technology is the only one which allows the non-linearity of the structure to be controlled at test conditions similar to operating ones. This model may be used to develop optimal control strategies and optimal sensor and actuator placement for active damping of the bridge. The reference mathematical model may be useful in simulating structural failure and different kinds of damage for training an automatic monitoring system based on an artificial neural network to detect, recognise and localise the damages at bridge operating conditions.
Keywords: full-scale modal testing, bridge vibrations testing, civil engineering structures, modal response, servo-hydraulic excitation, finite element model updating, structural modification, damage detection, neural networks, active vibration control
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