Frequency Identification And Damage Detection Of Bridges Based On Indirect Method

The modal parameter of a bridge,including natural frequency,mode shape and damping,is of great significance.For whatever engineering applications of a bridge,i.e.model updating,structural health monitoring or damage detection,the core premise is that the modal parameter of the bridge be accurately obtained.For the past decades,the direct method that requires a multitude of sensors installed directly on the bridge to record the bridge response,has been frequently used for bridge monitoring.In 2004,Yang et al.proposed a novel idea of collecting the vibration data of a bridge through the few sensors installed on a moving vehicle,which is referred as the indirect method.Since the indirect method outperforms the direct method in terms of convenience,costs and mobility,a growing number of scholars are devoted to the research of the indirect method.First,based on the vehicle-bridge interaction system,the analytical solution of the contact-point and the vehicle response are derived.Second,the instantaneous amplitude squared(IAS)of the driving component is extracted by band-pass filter and Hilbert transform,demonstrating that the IAS contains dense information of the bridge for damage detection.And the IAS of the driving component of the vehicle response and that of the contact-point response are compared theoretically and numerically,which reveals the existing influence of spectral leakage.In numerical simulation,the damage is deemed as a crack simulated by an internal hinge with a spring.In order to verify the feasibility of the damage detection method based on the IAS,the effects of damage parameter,vehicle speed,vehicle damping,measurement noise and road roughness are studied.As for the bridge frequency identification from the vehicle acceleration response,two algorithm named empirical mode decomposition(EMD)and complete ensemble empirical mode decomposition(CEEMD)are studied.Besides,the influence of the standard deviation of the noise introduced by CEEMD are also investigated.Conclusions are drawn at the end of each chapter.