Macro Strain-based Damage Identification Method For Municipal Highway Viaduct

As one of the mainstream of the three-dimensional highway engineering,municipal viaduct has been widely used due to its outstanding advantages of less investment,shorter construction period and less impact on ground traffic.To continuously monitor the municipal viaduct and to rapidly find structural damage by using the(quasi-)distributed strain sensing technology without interruption of traffic is still a challenge.This is vital to guarantee the safety operation of the municipal viaduct.Therefore,the damage identification method base on macro strain for municipal viaduct are studied through theoretical derivation,numerical simulation and experimental demonstration.The main contents are as follows:1.The proposed dynamic index of “Frequency Domain Operational Macro Strain Shape”(1)Macro strain frequency response function(SFRF)and Macro strain transmissibility function(STF)was deduced from the basic structural dynamics and the principle of fiber Bragg grating sensors,and accordingly the dynamic index of “Frequency Domain Operational Macro Strain Shape(OMSS)was proposed.Further,the corresponding physical meaning was explained,as well as the mathematical expression.Lastly,three identification methods were made.The physical meaning of the index are clear,simple and reliable.(2)The characteristics of OMSS are analyzed through the discussion of the zeroes,poles and STF of the system.The relations and difference between OMSS and macro strain mode(SMS)are described.Taking the simply supported beam as a tool,the effects of different frequency,excitation position and excitation type on OMSS are discussed.(3)Based on the three key components of OMSS,such as macro strain,system zeroes and STF,Sensitivities to the changes of structural characteristic parameters are derived,respectively.It is proved that OMSS is highly sensitive to local damage of the structure.2.Structural damage identification under stationary and non-stationary excitation(1)The structural damage localization method based on OMSS was proposed,and the structural damage tracking identification method based on STF was also proposed.The availability of the proposed methods under stationary excitation was verified by numerical examples.(2)The difficulties of bridge modal identification caused by the non-stationary vehicle excitation were interpreted by virtue of field test data of a real bridge.The reason that the poor identified result of damage localization under the non-stationary excitation was analyzed,and the recommending solutions were proposed.The method of structural damage identification method based on OMMS was further developed by using the two critical steps of “frequency determination”.Finally,the effectiveness of the method was verified by numerical cases.3.The application of structural damage identification under vehicle-bridge coupling(1)The dynamic model of vehicle-bridge coupling system was created,and the influence of factors such as road roughness,vehicle running speed and vehicle-bridge mass ratio on damage identification effect was comprehensively considered.Aimed at the time-varying parameter system,the probability of damage misjudgment to intact structures was reduced by using the Shewhart control chart in statistical theory,and the accuracy of identified results of the damaged structure was also improved.(2)Dynamic test was carried out on a three-span continuous girder bridge model with different degrees of damage in the laboratory.Force hammer impact and vehicular load excitation was adopted to verify the accuracy of the OMSS index and the effectiveness of the damage identification method.(3)It is verified that the instantaneous STF is a useful tool to realize the “critical processes I” in the “frequency determination” issue.It also gives the key technical guidance to the damage identification in a real project.(4)Taking a municipal viaduct as engineering application background,a refined structure and vehicle model was established.Operational and monitoring status of the bridge were simulated,which based on ANSYS software and multi-body dynamics theory.Damage locating and tracking to assumed damages in the viaduct was successfully implemented,according to analyzing the macro strain response data of the structure.Finally,the rapid damage identification process of municipal viaduct based on macro strain was presented.The main contributions made in the thesis:(1)The dynamic index of “frequency domain macro strain working deformation(OMSS)” was proposed to describe the frequency domain linear or nonlinear dynamic behavior of the structure under forced vibration.It is proved that OMSS is highly sensitive to the changes of structural characteristic parameters.Damage localization method based on OMSS was thereby developed.(2)The key issue of “frequency determination” can be solved through the two critical steps of “seeking system poles in forward thinking way” and “finding the weakest influence frequencies in reverse thinking way”.The accuracy of the result of damage localization to time-varying parameter system(vehicle-viaduct coupling system)under non-stationary excitation was ensured.(3)The damage tracking identification method of the structure was proposed,which based on the correlations of STFs between the local damaged and undamaged area of the structure.Consequently,the degree and speed of damage deterioration of the structure can be closely observed.