Damage detection for bridge structures under vehicle loads based on frequency decay induced by breathing cracks

Concrete cracking is one of the most common types of damage in bridges. It is essential to detect the damage early to avoid irreparable accident. In order to resolve the issue, a rapid damage detection method without base-line data is proposed for bridge structures. Vehicles passing across the damaged area of the bridge will lead to the opening of partial concrete cracks which closed without vehicle loads. The opening of cracks will cause a change of structural stiffness, which is reflected in decay of bridge frequency in a short time. Firstly, the influence factors of bridge frequency are introduced, and the influence of vehicle on the nth frequency of the bridge in vehicle-bridge interaction system (VBI) is deduced theoretically. Then, the damage index D based on the frequency decay induced by breathing cracks and the flowchart of damage detection are proposed, and the efficacy of the method is verified numerically. Finally, the proposed method is validated by experiments and a parametric analysis is carried out. Results show that breathing crack type damage in concrete bridges can be identified using this method, and the damage index is positively correlated with the extent of damage.