Model Updating for SMART Load Rating of Bridges

1. Model Updating for SMART Load Rating of Bridges Chang-Guen Lee / Won-Tae Lee Korea Expressway Corporation Jong-Jae Lee / Young-Soo Park Sejong University, Korea

2. Controlled or Blocked Traffic Measuring Deflection or Strain • Why Load Carrying Capacity? • Increase of the Number of Deteriorated Bridges • Prognosis of Remaining Lives • Widely Used as an Index for Bridge Integrity Conventional Load Rating Test Smart Load Rating of Bridges Using Ambient Acceleration Data Conventional loading tests Deteriorated bridges Inconvenient & Increase of logistics cost A lot of time & cost for field tests • Load Carrying Capacity of a Bridge (MOCT, 2005, Korea) • Pr : Design liveload : DB-24 (43.2tonf)* • RF : Rating factor by static analysis using the initial FE model • Kd : the deflection correction factor - by static loading tests • Ki : the impact correction factor - by dynamic loading tests • Kr, Kt : the other correction factors - empirically estimated • *DB-24 : Korean design code for highway bridge about 1.3 times of HS-20, AASHTO

3. Advantages Conventional methodusing truck loading tests SMART Load Rating Correction of FE modelusingdynamic characteristics of bridges Correction of analysis results usingstatic deflection (strain) data • Advantages • No need to control or block traffics • Easier to measure acceleration rather than strain/deflection • High reliability by continuous measurements • Less time- and labor-consuming Deflection Correction Factor (Kδ) *Other Correction Factors – Empirically Estimated (usually 1.0) modelupdating Conventional Proposed

4. Procedure 1 Ambient acceleration data excited by ordinary traffic on a bridge without traffic control are measured. Based on the modal properties extracted from the ambient vibration data, the initial finite element (FE) model of the bridge can be updated to represent the current real state of a bridge. Using the updated FE model, the deflection akin to the real value can be easily obtained without measuring the real deflection. Based on the deflection values from initial and updated FE models, deflection correction factor can be obtained. Procedures Ambient vibration tests Model updating Load Rating Modal Analysis Initial FE model Updated FE model Planning of Vibration Tests Simulation of truck loading tests Measuring Ambient Acceleration Estimation of Deflection Correction Factor (Kδ) Evaluation of Load Carrying Capacity Modal parameter ID Modal Parameter Identification Updating Initial FE Model No Yes Updated FE model Analysis = Exp. Modes

5. Procedure 2 Modal Parameter ID Using Ambient Vibration Tests FE Model Updating Experimental modal analysis has drawn lots of attention from structural engineers for updating the analysis model and estimating the present state of structural integrity. Ambient vibration tests under wind, wave, or traffic loadings may be effective for large civil-infra structures. Several modal parameter identification methods without using input information in the frequency and the time domain are available, such as Frequency Domain Decomposition (FDD) and Stochastic Subspace Identification (SSI), etc. Using the extracted modal properties, the initial FE model is updated using various kinds of optimization algorithms. The objective function can be constructed using the differences between the measured and estimated natural frequencies, and the constraint equations were considered to limit the differences between the measured and estimated mode shapes as Downhill Simplex SV functions in FDD Genetic Algorithms Stabilization Chart in SSI

6. Proof Tests The Korea Expressway (KEX) test road is a 2-lane one-way expressway built in parallel to Jungbu Inland Expressway in Korea. The total length of the test road is 7.7km, and there are three bridges along the test road. A series of conventional truck loading tests and ambient vibration tests were carried out to prove the proposed SMART Load Rating scheme. Ordinary Expressway Korea Expressway Corporation (KEX) Test Road Samseung Br. (SPG) Yeondae Br. (STB) Geumdang Br. (PSCB)

7. Proof Test 1 : Samseung Br. FE Model of Samseung Br Ambient Vibration Tests Model Updating Modal Parameter ID Natural Frequencies and Mode shapes of initial FE model and measured ones(Lower 6 modes) Accelerometer LDVT F1=4.01Hz(4.19) F2=4.25Hz(4.83) F3=12.80Hz(11.58) Downhill Simplex Method (Nelder and Mead, 1964) was used. No. of accelerometers : 16EA Sampling Frequency : 200Hz Comparison of Deflection Correction Factors (Kδ) • Kδ by the SMART Load Rating is • in a reasonable range compared with Kδ by the conventional method • more consistent in seasonal variation (summer and winter) F4=13.37Hz(12.90) F5=17.24Hz(14.74) F6=21.60Hz(18.37)

8. Proof Test 2 : Geumdang Br. Modal Parameter ID Model Updating Natural Frequencies and Mode shapes of initial FE model and measured ones(Lower 4 modes) Ambient Vibration Tests Accelerometer Downhill Simplex Method(Nelder and Mead, 1964) LDVT No. of accelerometers : 16EA Sampling Frequency : 200Hz Comparison of Deflection Correction Factors (Kδ) F1=2.89Hz (2.99) F2=4.02Hz(4.47) F3=4.69Hz(5.03) F4=7.61Hz(7.51)

9. Applications to Highway Bridges Palgok III Br.(1996) STB L=230m (40+3@50+40) Measurement system installed at the inside of the steel box girder Ambient Vibration TestsInside of the steel box girder Dundae IV Br.(1996) STB L=310m (45+4@55+45) Gahwacheon (1992) PSCB L=290m (60+120+60+50) Sensor Installation along the sideway Yeondong Br.(1996) PSCB L=170m (35+50+50+35) Sensor Installation inside the box

10. Integrated GUI-based SMART Load Rating Integrated GUI Ambient vib. tests Using smart sensors Automated Modal Parameter ID SMARTLoad Rating Model updating Selection of updating variables FE model using Commercial S/W(SAP2k or MIDAS) Integrated GUI-based SMART Load Rating System

11. Field Test on NJ Bridge SB-Span2 FE Model Frame 1448 Shell 1401

13. Field Test on NJ Bridge SB-Span2

14. Field Test on NJ Bridge Test Equipments

15. Field Test on NJ Bridge SB-Span2 Testset #1 Lateral Vertical Testset #2

16. Field Test on NJ Bridge SB-Span2

17. Field Test on NJ Bridge SB-Span2 Testset #1 Testset #2 `

18. Field Test on NJ Bridge SB-Span2 Natural Frequencies [Hz]

19. Field Test on NJ Bridge SB-Span2 Comparison of identified modal properties 2.615 2.72 3.55 3.70 6.15 5.14

20. Field Test on NJ Bridge SB-Span2 Comparison of identified modal properties 10.59 7.75 8.92 7.66 12.13 11.4

21. Field Test on NJ Bridge SB-Span2 Sensitivity of Updating Variables Slab Girder - web Spring at support (longitudinal dir.) ( ton – m ) Cross beam

22. Field Test on NJ Bridge SB-Span2 Design Variables

23. Field Test on NJ Bridge SB-Span2 Conclusions and Future Works • Application of Smart Load Rating Procedures • Modal parameter ID of the test bridge • Selection of Design Variables in Model Updating • Low lateral modes (butterfly modes) of the test bridge bad condition in concrete slab and cross beam  require more detail investigations on FE model & test data • Verification of the updated FE model  Truck loading tests • Effects of considered modes / design variables

24. Field Test on NJ Bridge SB-Span2 Variation of Natural frequencies

25. Field Test on NJ Bridge SB-Span2 Lateral Motion

26. Field Test on NJ Bridge SB-Span2 DAQ System Check-up : Inner Clock

27. Field Test on NJ Bridge SB-Span2 Natural Frequencies [Hz]