Bridge Modal Identification And Damage Detection Under Vehicle Scanning Method

The extremely large number of small and medium-sized span bridges bear increasing traffic loads and material degradation,posing significant safety risks.Promoting bridge modal information and damage identification is of great significance for achieving rapid detection of road network bridges.Based on the vehicle scanning method(VSM)as the research background,this paper proposes a method for synchronous identification of bridge frequencies and modal shapes using two axle on-board sensors,carries out equivalent damage relationships for different damage numerical simulation methods,and further studies on damage identification using bridge modal information.Model tests are conducted using a laboratory scaled vehicle bridge system to verify.The main research contents and achievements include:(1)A practical method of multi degree of freedom dual axis vehicle scanning bridge modal shapes is proposed.Firstly,a closed form solution of the interaction between a symmetric biaxial vehicle and a simply supported beam is derived,and a novel bimodal spectral idealized filtering method is used to synchronously identify the bridge frequency and modal shape from the vehicle acceleration response;Then,the proposed method for synchronous identification of bridge frequencies and vibration modes is validated by numerical simulation,and the effects of vehicle speed,vehicle parameters,damping,road roughness,and environmental noise on the method are analyzed parametrically.The results show that the proposed method can synchronously identify bridge frequencies and modal shapes in the presence of high-speed vehicles(such as 20 m/s),various vehicle parameters,vehicle and bridge damping,road roughness,and environmental noise.Road roughness and environmental noise pollute the bimodal spectrum of bridge frequencies,but as long as the bridge frequencies are visible in the spectrum,the proposed method is feasible.(2)Comparative studies were conducted on different damage modeling techniques for beam structures,and the impact of vehicle bridge coupling(VBI)responses on structural health monitoring(SHM)was evaluated.Firstly,the theoretical basis of four damage modeling techniques,namely,element stiffness loss,element mass increase,cracked beam element,and cracked spring element,is analyzed,and a criterion of the same frequency is proposed to simplify the equivalent relationship;Then,the VBI system consisting of a biaxial vehicle and a damaged beam structure was simulated using VBI elements,and the correctness of the four VBI damage simulation programs was verified by modal curvature difference indicators.Finally,the impact of different damage modeling techniques on the dynamic response of VBI systems under a unified damage level is compared,and the possibility of using vehicle and bridge responses for damage identification under different damage modeling techniques is compared.The results show that under the same damage level of 5% to 30%,the dynamic responses of VBI systems generated by different damage modeling techniques differ significantly.Vehicle response is more sensitive to damage than bridge response.The crack spring beam element method has the greatest impact on VBI response.The crack beam element method has a similar impact to the element stiffness loss method,while the impact of the element mass increase method can be ignored.When dealing with vehicle acceleration responses during the damage identification exploration,it was found that three methods other than the element mass increase technique could be used to identify the location and extent of damage,but the amplitude change of the crack spring element method was not so significant.(3)Model tests were conducted to verify the above two parts.First,a vehicle bridge interaction(VBI)test was conducted to extract modal vibration patterns from the vertical acceleration of a two axle model vehicle as it passes through the bridge.The results verified that the acceleration of a two axle vehicle can successfully identify the bridge frequency and high-precision modal vibration patterns.Secondly,a bridge damage test was conducted,and the damage was simulated in the form of additional mass blocks and cut sections.The study used IAS indicators to locate the damage location from vehicle acceleration.The results verified that both methods can successfully locate the damage location at a certain level.On the one hand,this study verifies the feasibility of using two axle vehicles for modal vibration mode identification of bridges,providing convenience for the extensive engineering application of vehicle scanning method in indirect bridge monitoring.On the other hand,the possibility of obtaining direct bridge responses and indirect vehicle responses through these different damage modeling techniques to detect bridge damage has been studied,which is of great significance for analyzing the impact of vibration responses of VBI systems under damage.It can provide a reference for using different damage models for numerical simulation,selecting appropriate and even developing more practical damage detection techniques.