Theoretical investigation of the use of a moving vehicle to identify bridge dynamic parameters

1. Theoretical investigation of the use of a moving vehicle to identify bridge dynamic parameters Patrick McGetrick Dr. Arturo González Prof. Eugene OBrien

2. Introduction • A Rational Transport Policy must aim to: • Maintain traffic safety • Ensure adequate maintenance is provided • Maintain levels of transport capacity • Budget accordingly • Therefore bridge structures need to be monitored as they are subject to continuous degradation due to traffic, ageing and environmental factors

3. Introduction • Increasingly, larger bridges are being instrumented and monitored on an ongoing basis • Measuring bridge modes and frequencies of vibration • Direct Installations – Expensive, time consuming 3

4. Research Outline • “Theoretical investigation of the use of a moving vehicle to identify bridge dynamic parameters” • Developing a low cost indirect method • Use of instrumented vehicle: measure vertical vibration using accelerometers • Monitor dynamic response →Bridge damping Accelerometer fitted to axle Vehicle → (Source: Enrique Covián, University of Oviedo)

5. Bridge structural damping • Bridge structural damping has been chosen to be the focus of the research as it is damage sensitive; in a simple model damage to the bridge can be simulated by changing the level of damping

6. Advantages • No on-site installation of measurement equipment • Enables more effective and efficient widespread monitoring of existing bridge structures’ condition i.e. numerous structures could be monitored in one day • Required maintenance can be instigated at an earlier stage in degradation, which (usually) results in less costly repairs

7. Background Information • Yang et al indicated the feasibility of extracting bridge frequencies from the dynamic response of a vehicle passing over a bridge using a simple model • The technique was later verified experimentally by Lin & Yang, observing that it was easier to extract the bridge frequency for vehicle speeds less than 40km/h (11.1m/s)

8. Background Information • González et al investigated the method both experimentally and using a 3D FEM model • Accurate determination of the bridge frequency is feasible for low speeds & when the degree of dynamic excitation of the bridge is high enough • Influence of road profile on vehicle vibration prevented the identification of the bridge natural frequency (Source: Enrique Covián, University of Oviedo)

9. Theoretical Testing • Methodology • Simulate vehicle-bridge dynamic interaction using computer model in MATLAB varying: • Road Profile (Smooth & ISO Class A) • Vehicle Velocities (5m/s - 25m/s) • Vehicle Mass (10t & 20t) • Bridge Spans (15m, 25m & 35m)

10. Methodology cont. • Also, vary dynamic properties of each bridge span i.e. Damping varied between 0% - 5% • Obtain bridge frequency & measure dynamic response of vehicle to changes in damping in the frequency spectra of vertical vehicle accelerations

11. Matlab Simulation Model • Quarter Car & Euler-Bernoulli beam

12. Quarter Car Properties

13. Bridge Properties

14. Processing Acceleration Data • Vehicle Acceleration Data processed using MATLAB FFT functions • Peaks obtained Example of acceleration data & processed acceleration data for Quarter Car-bridge interaction system

15. Smooth Profile Results

16. 15m Span, Spectra for 20m/s Acceleration spectra for tyre mass @20m/s on 15-m bridge showing higher energy for lower bridge damping values, quarter car mass is 10t

17. 15m Span PSD-damping trends Minimum 16% decrease in peak PSD for a 1% increase in damping Peak PSD-damping trends at bridge frequency peak for tyre mass on 15-m bridge, showing higher sensitivity for lower velocity

18. 25m Span, Spectra for 20m/s Acceleration spectra for tyre mass @20m/s on 25-m bridge showing higher energy for lower bridge damping values

19. 25m Span PSD-damping trends Minimum 20% decrease in peak PSD for a 1% increase in damping Peak PSD-damping trends at bridge frequency peak for tyre mass on 25-m bridge, showing higher sensitivity for lower velocity

20. 35m Span, Spectra for 20m/s Acceleration spectra for tyre mass @20m/s on 35-m bridge, again showing higher energy for lower bridge damping values

21. 35m Span PSD-damping trends Minimum 20% decrease in peak PSD for a 1% increase in damping Peak PSD-damping trends at bridge frequency peak for tyre mass on 35-m bridge, showing higher sensitivity for lower velocity

22. Frequency Results Estimated and true bridge frequency for all bridge spans and velocities (10t & 20t)

23. ISO Class A Profile Results

24. 15m Span, Spectra for 20m/s Acceleration spectra for tyre mass @20m/s on 15-m bridge showing higher energy for lower bridge damping values @ vehicle peak, quarter car mass is 10 tonnes

25. 15m Span, Spectra for 5m/s Acceleration spectra for tyre mass @5m/s on 15-m bridge showing bridge frequency peak & vehicle peak, quarter car mass is 10 tonnes

26. 15m Span PSD-damping trends Maximum 2.8% decrease in peak PSD for a 1% increase in damping Peak PSD-damping trends at bridge frequency peak for tyre mass on 15-m bridge, vehicle velocity 5m/s

27. 15m Span PSD-damping trends Maximum 0.35% decrease in peak PSD for a 1% increase in damping Peak PSD-damping trends at vehicle frequency peak for tyre mass on 15-m bridge, vehicle velocity 5m/s

28. Conclusions • Smooth Profile: • Bridge frequency peak was detected for all velocities • Frequency peak diverges from bridge frequency as velocity increases • For all vehicle velocities a decrease in Peak PSD with increasing damping level was found: suggests that it is possible to monitor bridge damping through vehicle acceleration measurements • Higher Sensitivity of Peak PSD to a 1% change in damping for: lower velocities, longer bridge span, changes between lower damping levels; • Maximum 71% for 35m span @5m/s, minimum 16% for 15m span @25m/s

29. Conclusions • ISO Class A Profile: • Bridge frequency peak only detected @5m/s, Tyre Mass frequency peak detected • The road profile’s influence on the vehicle vibration dominates the spectra, hiding the bridge frequency. • This influence also masks changes in the bridge damping properties • However, for all vehicle velocities a decrease in Peak PSD with increasing damping level still existed @ obtained peaks

30. Acknowledgements • The authors wish to express their gratitude for the financial support received from the 7th European Framework ASSET Project towards this investigation.

31. Thank You

32. References • 1. Y B Yang, C W Ling and J D Yau, ‘Extracting bridge frequencies from the dynamic response of a passing vehicle’, Journal of Sound and Vibration, 272, pp 471-493, 2004. • 2. C W Ling and Y B Yang, ‘Use of a passing vehicle to scan the fundamental bridge frequencies. An experimental verification’, Engineering Structures, 27, pp 1865-1878, 2005. • 3. A González, E Covián and J Madera, ‘Determination of Bridge Natural Frequencies Using a Moving Vehicle Instrumented with Accelerometers and GPS’, Proceedings of the Ninth International Conference on Computational Structures Technology, Athens, Greece, paper 281, September 2008. • 4. R O Curadelli, J D Riera, D Ambrosini and M G Amani, ‘Damage detection by means of structural damping identification’, Engineering Structures, 30, pp 3497-3504, 2008. • 5. D Cebon, ‘Handbook of Vehicle-Road Interaction’, Swets & Zeitlinger, the Netherlands, 1999. • 6. ISO 8608:1995, ‘Mechanical vibration-road surface profiles-reporting of measured data’, International Standards Organisation, 1995.