icshmim2016成都v803分會場報告tian yon

1、Structural Flexibility Identification of a Pre-stressed Concrete Continuous Box Girder Bridge Based on Ambient Vibration TestYongDing Tian Email: Civil Engineering, Southeast University, ChinaThe 3rd International Conference on Structural Health Monitoring and Integrity Management(ICSHMIM 2016)Conte

2、ntsIntroductionBridge overview, sensor layout and field testUn-scaled flexibility identificationScaled flexibility identification based on FEMScaled flexibility identification by mass changingConclusions123456Introduction Over 300 long-span bridges have been installed SHM systems.Ambient vibration t

3、est can only outputs basic modal parameters, such as natural frequency, unscaled mode shapes Sutong Bridge, Chinaaccelerometer（30）displacement gauge（8）Strain gauge（223）thermometer（89）GPS（4）hygrometer（2）anemometer（2）Jiangyin Bridge, ChinaOver 170 sensorsOver 300 sensorsCurrent SituationChallenging Pr

4、oblemSHM systems are useful for early warning of sudden events (e.g., ship collision)Collaborated with JTRIThe limitation of current ambient vibration testIntroductionImpact vibration testStructural ResponseImpact ForceExpensive experimental costThe available excitation equipment are limitedMainly w

5、orks for short/middle span bridgesTraffic controlLimited impact testing technologyHigh magnitude impacting forceImpact vibration test is another method widely used for SHMLimitationsThe limitation of impact vibration testScaled flexibilityIdentification by Using the Mass changingstrategyScaled flexi

6、bilityIdentification by Using the Mass matrix ofEstablished FEMUnscaled flexibilityIdentification by Deriving the Relationship of FRFMagnitude IntroductionThe scope of this paperAn ideal concept is whether we can identify structural flexibility from the easy-performing ambient vibration test or not.

7、Fstatic loadf unit forceFlexibility is defined as:0Method 1Method 2Method 3Bridge overviewBridge description, sensor layout, ambient vibration test (c)(a)(b)The investigated structure is a three-span post-tensioned continuous concrete bridge In ambient vibration tests, responses of the structure wit

8、h and without mass changing by using trucks with a 60 ton weight were measured.Ambient Vibration Test(b)(c)Bridge overviewStatic truck load test Static Truck Load TestIn static test, static strain were measured when two trucks were located at lanes 2 and 3 of the middle main spanUnscaled flexibility

9、 identificationAveraged AccelerationCorrelationFunctionUnscaledFRFUn-scaled FRF estimation from ambient test data of studied bridgeFlowchart of FRF estimation Unscaled flexibility identificationThe FRF magnitude estimated from ambient test data is proportional to that estimated from impact test data

10、ConclusionsThe relationship of estimated FRFsUnscaled flexibility identificationTheoretical derivationFRF estimated from impact test data:Unscaled FRF estimated from ambient test data:The relationship between FRF magnitude:Un-scaled flexibilitySimplifyThese basic modal parameters can be obtained fro

11、m ambient test dataUnscaled flexibility identificationUnscaled flexibility of studied bridge(b)(a)(c)(d)(a)Basic modal parameter identificationUnscaled flexibilityPredicted deflectionScaled flexibility identificationBased on FE modelingEstablishing FE modelExtracting mass matrixMass-normalized mode

12、shapeScaled flexibilityScaled flexibility identificationBased on mass changing methodAmbient vibration test of unmodified structureOperational Modal Analysis(Frequency, unscaled mode shape)Ambient vibration test of modified structureOperational Modal Analysis(Frequency, unscaled mode shape)Mass-norm

13、alizedscaling factorMass-normalized mode shapeScaled FlexibilityThe schematic diagram of scaled flexibility identification using mass changing strategyScaled flexibility identificationBased on mass changing methodThe eigenvalue equation of modified structure for the ith modeThe mode shapes of the mo

14、dified structure can be expressed as a linear combination of unmodified mode shapes:The relationship between matrixPre-multiplying Eq.(1) with the unmodified mass-normalized mode shape vectorScaled flexibility identificationBased on mass changing methodMass-normalized mode shape identificationConclu

15、sionsThe un-scaled flexibility identification method has been proposed from ambient vibration test data which is meaningful for engineers to understand the relative stiffness distribution of the structure.A FE modeling-based scaled flexibility identification method has been studied. It directly extr

16、acts lumped mass matrix from the established finite element model. Another scaled flexibility identification method using mass-change strategies has been proposed. It directly uses the basic modal parameters of unmodified and modified structures obtained from ambient test data to calculate mass-norm

17、alized mode shape and scaled flexibility. The predicted deflections from the identified flexibility agree well with those obtained from static test, which successfully verified the reliability of the proposed method. The results illustrates that structural flexibility can be identified from ambient vib