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

parameters

Patrick McGetrickDr. Arturo GonzálezProf. Eugene OBrien

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• A Rational Transport Policy must aim to:Maintain traffic safetyEnsure adequate maintenance is providedMaintain levels of transport capacityBudget accordingly

Introduction

• Therefore bridge structures need to be monitored as they are subject to continuous degradation due to traffic, ageing and environmental factors

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• Increasingly, larger bridges are being instrumented and monitored on an ongoing basis

• Measuring bridge modes and frequencies of vibration

Introduction

• Direct Installations – Expensive, time consuming

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Research Outline• “Theoretical investigation of the use of a moving

vehicle to identify bridge dynamic parameters”

Developing a low cost indirect methodUse of instrumented vehicle: measure vertical vibration using accelerometersMonitor dynamic response → Bridge damping

Accelerometer fitted to axle

Vehicle →

(Source: Enrique Covián, University of Oviedo)

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• 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

Bridge structural damping

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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

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• 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)

Background Information

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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)

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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)

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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

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Matlab Simulation Model• Quarter Car & Euler-Bernoulli beam

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Quarter Car Properties

Property Model 1 (10 tonnes)

Model 2 (20 tonnes)

Body mass, ms 9000 kg 19000 kgTyre mass, mu 1000 kg 1000 kg

Suspension Stiffness, Ks 8x104 N/m 8x104 N/mSuspension Damping, Cs 10x103 Ns/m 10x103 Ns/m

Tyre Stiffness, Kt 2x106 N/m 2x106 N/m

Body mass frequency of vibration, fbody

0.47 Hz 0.32 Hz

Tyre mass frequency of vibration, ftyre

7.26 Hz 7.26 Hz

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Bridge Properties

Span Length, L

(m)

Modulus of elasticity, E

(N/m2)

Second moment of area, J (m4)

Mass per unit length,

µ (kg/m)Structural damping, ξ

1st natural frequency of

vibration, fbridge (Hz)

15 3.5x1010 0.5273 28125 1% to 5% 5.6625 3.5x1010 1.3901 18358 1% to 5% 4.0935 3.5x1010 3.4162 21752 1% to 5% 3.01

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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

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Smooth Profile Results

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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

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15m Span PSD-damping trends

Peak PSD-damping trends at bridge frequency peak for tyre mass on 15-m bridge, showing higher sensitivity for

lower velocity

Minimum 16% decrease in peak PSD for a 1% increase in damping

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

25m Span, Spectra for 20m/s

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25m Span PSD-damping trends

Peak PSD-damping trends at bridge frequency peak for tyre mass on 25-m bridge, showing higher

sensitivity for lower velocity

Minimum 20% decrease in peak PSD for a 1% increase in damping

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

35m Span, Spectra for 20m/s

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35m Span PSD-damping trends

Peak PSD-damping trends at bridge frequency peak for tyre mass on 35-m bridge, showing higher

sensitivity for lower velocity

Minimum 20% decrease in peak PSD for a 1% increase in damping

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Frequency Results

Estimated and true bridge frequency for all bridge spans and velocities (10t & 20t)

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ISO Class A Profile Results

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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

15m Span, Spectra for 20m/s

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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

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15m Span PSD-damping trends

Peak PSD-damping trends at bridge frequency peak for tyre mass on 15-m bridge, vehicle velocity 5m/s

Maximum 2.8% decrease in peak PSD for a 1% increase in damping

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Peak PSD-damping trends at vehicle frequency peak for tyre mass on 15-m bridge, vehicle velocity 5m/s

15m Span PSD-damping trends

Maximum 0.35% decrease in peak PSD for a 1% increase in damping

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Conclusions• Smooth Profile:

Bridge frequency peak was detected for all velocitiesFrequency peak diverges from bridge frequency as velocity increasesFor 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 measurementsHigher 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

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Conclusions• ISO Class A Profile:

Bridge frequency peak only detected @5m/s, Tyre Mass frequency peak detectedThe road profile’s influence on the vehicle vibration dominates the spectra, hiding the bridge frequency.This influence also masks changes in the bridge damping propertiesHowever, for all vehicle velocities a decrease in Peak PSD with increasing damping level still existed @ obtained peaks

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Acknowledgements

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

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Thank You

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References1. 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.