Bridge Damping Identification Based On A Two-axle Test Vehicle Scanning Method

As an important traffic artery,the bridge is also the node and throat of the transportation lifeline project.Its safety has been a concern.Damping,as an important dynamic parameter of the bridge structure,can measure the energy dissipation capacity of the structure against external loads and is also an important indicator for bridge safety performance evaluation.However,because the damping mechanism is more complicated and difficult to determine and quantify,there is no good theory and method.Therefore,it is necessary to study the theory and method of obtaining bridge damping,which is of great significance for the evaluation of bridge safety performance.In this paper,a theory and method for identifying the damping ratio of simply supported beams using a two-axle moving vehicle are presented.The main research contents are as follows:(1)The theoretical model of the two-axle moving vehicle acting on the simply supported beam is established,and the analytic solutions for dynamic response of simply supported beam and scanning points under two-axle moving vehicle are derived;(2)A method for identifying bridge damping based on dynamic response of scanning points is proposed.The bridge frequency correlation response is extracted from the scanning point response and its instantaneous amplitude is obtained by Hilbert transform,the theoretical solution of the bridge damping ratio can be obtained by dividing the instantaneous amplitude of the bridge frequency correlation response with fixed spacing;(3)In order to expand the applicability of the two-axle vehicle,the analytic solution of bridge damping ratio is established by asymmetric two-axle vehicle based on the symmetric two-axle vehicle.The coupled finite element model of vehicle and bridge is established.The numerical results and analytic results are compared.The effectiveness of symmetrical and asymmetric two-axle vehicles to identify bridge damping is verified.(4)The effect of the mass ratio of vehicle and bridge,vehicle damping,vehicle speed,environment noise and bridge surface roughness on the bridge damping identification is analyzed,which provides a theoretical basis for the development and optimization of the two-axle inspection vehicle system.The research results show that:(1)The scanning point response includes the bridge frequency partial response and the driving frequency related response,and the bridge frequency correlation response is obviously attenuated by the damping effect;(2)The bridge damping identification theory proposed in this study is based on the fact that the frequencies of the vehicle and bridge are made available.The vehicle and bridge frequencies should not be the same or similar to avoid resonance affecting the identification accuracy;(3)The change of vehicle damping hardly affects the identification of bridge damping.The smaller the vehicle speed and the mass ratio of vehicle and bridge,the better the identification effect;(4)For various bridges with damping,or the bridge surface roughness,environment noise and other interference factors exist,the method proposed in this study has better robustness;(5)Asymmetric two-axle vehicle has the same bridge damping identification effect as the symmetric two-axle vehicle,that is,they have the same analytic solution,and the influence laws of various parameters(the mass ratio of vehicle and bridge,vehicle speed,vehicle damping,bridge damping,bridge surface roughness,environmental noise,etc.)are consistent.