Modal Analyses of Two Concrete Bridges in Sweden

Measurements and analyses of dynamic response in concrete bridges have been performed. The purpose was to develop a reliable, nondestructive test-method for detection of serious damages in concrete structures. The project has given valuable experience, exposed several of the problems and also indicated requirements of equipment for future applications. Two concrete bridges were measured and analysed. Impact loads were used for excitations. In the first bridge, internal damage was introduced by overloading the mid-section in four different load-steps. After each step, a complete modal analysis was performed. In the second bridge, additional reinforcement in the form of steel plates were glued to the lower surface of the plate. Measurements of modal parameters were made before and after application of this reinforcement. Finally, the bridge was loaded to shear-failure, and another measurement of modal parameters was made. Small differences in resonant frequencies and relative damping coefficients were observed for both bridges. Differences in modal shapes were also observed.