Multi-Level Dynamic Testing Method with Adaptive Excitation Amplitude for Bridge Bearing Capacity Assessment

The deformation of existing bridges under external loads is a critical parameter reflecting the structural load-bearing capacity. Bridge load tests typically require the load to reach a specified load efficiency ratio to obtain the structural linear state and potential nonlinear state. Dynamic load testing serves as an efficient and economical method for obtaining load–deformation relationships of structures. However, conventional bridge dynamic tests are usually based on linear assumptions and are unable to assess structural nonlinear state under the goal load. This paper proposes a multi-level dynamic loading test theoretical framework for evaluating bridge bearing capacity. The proposed method utilizes structural quasi-linear responses under low load efficiency ratio to identify dynamic characteristic parameters and assess stiffness degradation states, while the potentially nonlinear response of the structure under a high load efficiency ratio is utilized to evaluate resistance degradation state. The study reveals the impacts of structural parameter change and strain rate effect on multi-level dynamic testing. Accordingly, an excitation amplitude adjustment method considering these two factors is derived. Compared with traditional dynamic testing, the proposed approach enables more comprehensive bridge service state evaluation without compromising testing efficiency. The effectiveness of the method is validated through a numerical example of a simply supported beam and an experimental example of a T-shaped continuous girder bridge.