Dynamic testing, structural identification and damage detection on Dogna’s bridge

The results of a series of harmonically forced tests carried out on a reinforced concrete single-span bridge subjected to increasing levels of an artificial damage are interpreted in this paper. The deck structure of the bridge consists of a slab and three simply supported beams. The damage is represented by a series of notches made on a lateral beam to simulate the effect of incremental concentrated damage. The variation of natural frequencies shows an anomalous increase in the transition {}from one intermediate configuration to the next damage configurations. Vibration modes shapes show an appreciable asymmetry, despite the nominal symmetry of the reference configuration of the bridge. A justification of this unexpected dynamic behavior is presented in this paper. The analysis is based on progressive identification of an accurate finite element model of the reference and damage configurations based on natural frequency and vibration modes measurement. Finally, changes in modal curvature of the first two modes evaluated along the main beams were successfully used to identify the location of the damage.