Frequency-avoiding in arch bridges: a possible structural health monitoring approach

The frequency avoiding of natural frequency loci and the modal shapes hybridization are typical phenomena which take place, among other cases, in initially curved structures with a simmetry-defect, when a control parameter is varied. The phenomenon plays a key role in the explanation of a modal hybridization evidenced during the experimental tests on the “Valle Castellana” concrete, twin-arches, bridge (Provincia di Teramo, Italy). In the same way, due to high sensitivity of the hybrid modal shapes to the imperfections, the occurrence of those phenomena could be conveniently used in structural health monitoring programs. In this paper, a linear model of plane arch with an imperfection in a specific cross-section, is used as a tool in the interpretation of the behavior observed in the mentioned bridge.