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AMBIENT VIBRATION MONITORING Helmut Wenzel VCE Holding GmbH, Vienna, Austria Dieter Pichler VCE Holding GmbH, Vienna, Austria

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  • AMBIENT VIBRATIONMONITORING

    Helmut WenzelVCE Holding GmbH, Vienna, Austria

    Dieter PichlerVCE Holding GmbH, Vienna, Austria

    Innodata0470024313.jpg

  • AMBIENT VIBRATIONMONITORING

  • AMBIENT VIBRATIONMONITORING

    Helmut WenzelVCE Holding GmbH, Vienna, Austria

    Dieter PichlerVCE Holding GmbH, Vienna, Austria

  • Copyright 2005 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester,West Sussex PO19 8SQ, England

    Telephone (44) 1243 779777Email (for orders and customer service enquiries): [email protected]

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    or emailed to [email protected], or faxed to (44) 1243 770620.Designations used by companies to distinguish their products are often claimed as trademarks.

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  • Contents

    PREFACE xi

    ACKNOWLEDGEMENTS xiii

    SUMMARY xv

    1 INTRODUCTION 1

    1.1 Scope of Applications 11.2 Laws and Regulations 21.3 Theories on the Development of the AVM 4

    2 OBJECTIVES OF APPLICATIONS 7

    2.1 System Identification 72.1.1 Eigenfrequencies and Mode Shapes 82.1.2 Damping 112.1.3 Deformations and Displacements 112.1.4 Vibration Intensity 122.1.5 Trend Cards 13

    2.2 Stress Test 132.2.1 Determination of Static and Dynamic

    Stresses 142.2.2 Determination of the Vibration Elements 142.2.3 Stress of Individual Structural Members 152.2.4 Determination of Forces in Tendons

    and Cables 15

  • 2.3 Assessment of Stresses 172.3.1 Structural Safety 172.3.2 Structural Member Safety 192.3.3 Maintenance Requirements and Intervals 192.3.4 Remaining Operational Lifetime 21

    2.4 Load Observation (Determination of External Influences) 212.4.1 Load Collective 212.4.2 Stress Characteristic 212.4.3 Verification of Load Models 232.4.4 Determination of Environmental Influences 242.4.5 Determination of Specific Measures 242.4.6 Check on the Success of Rehabilitation

    Measures 252.4.7 Dynamic Effects on Cables and Tendons 252.4.8 Parametric Excitation 27

    2.5 Monitoring of the Condition of Structures 282.5.1 Assessment of Individual Objects 292.5.2 Periodic Monitoring 312.5.3 BRIMOS Recorder 312.5.4 Permanent Monitoring 342.5.5 Subsequent Measures 35

    2.6 Application of Ambient Vibration Testing toStructures for Railways 352.6.1 Sleepers 362.6.2 Noise and Vibration Problems 39

    2.7 Limitations 492.7.1 Limits of Measuring Technology 492.7.2 Limits of Application 512.7.3 Limits of Analysis 522.7.4 Perspectives 53

    References 54

    3 FEEDBACK FROM MONITORING TO BRIDGEDESIGN 55

    3.1 Economic Background 553.2 Lessons Learned 56

    3.2.1 Conservative Design 563.2.2 External versus Internal Pre-stressing 573.2.3 Influence of Temperature 573.2.4 Displacement 613.2.5 Large Bridges versus Small Bridges 643.2.6 Vibration Intensities 66

    vi Contents

  • 3.2.7 Damping Values of New Composite Bridges 683.2.8 Value of Patterns 683.2.9 Understanding of Behaviour 723.2.10 Dynamic Factors 72

    References 75

    4 PRACTICAL MEASURING METHODS 77

    4.1 Execution of Measuring 784.1.1 Test Planning 834.1.2 Levelling of the Sensors 834.1.3 Measuring the Structure 84

    4.2 Dynamic Analysis 844.2.1 Calculation Models 844.2.2 State of the Art 88

    4.3 Measuring System 894.3.1 BRIMOS 894.3.2 Sensors 904.3.3 Data-Logger 914.3.4 Additional Measuring Devices and Methods 92

    4.4 Environmental Influence 934.5 Calibration and Reliability 964.6 Remaining Operational Lifetime 97

    4.6.1 Rainflow Algorithm 984.6.2 Calculation of Stresses by FEM 1014.6.3 SN Approach and Damage Accumulation 1044.6.4 Remaining Service Lifetime by Means of Existing

    Traffic Data and Additional Forward andBackward Extrapolation 105

    4.6.5 Conclusions and Future Work 106References 109

    5 PRACTICAL EVALUATION METHODS 111

    5.1 Plausibility of Raw Data 1115.2 AVM Analysis 112

    5.2.1 Recording 1125.2.2 Data Reduction 1145.2.3 Data Selection 1155.2.4 Frequency Analysis, ANPSD (Averaged Normalized

    Power Spectral Density) 1155.2.5 Mode Shapes 1205.2.6 Damping 1215.2.7 Deformations 123

    Contents vii

  • 5.2.8 Vibration Coefficients 1255.2.9 Counting of Events 126

    5.3 Stochastic Subspace Identification Method 1295.3.1 The Stochastic Subspace Identification (SSI) Method 1295.3.2 Application to Bridge Z24 130

    5.4 Use of Modal Data in Structural Health Monitoring 1345.4.1 Finite Element Model Updating Method 1345.4.2 Application to Bridge Z24 1415.4.3 Conclusions 147

    5.5 External Tendons and Stay Cables 1495.5.1 General Information 1495.5.2 Theoretical Bases 1505.5.3 Practical Implementation 1505.5.4 State of the Art 1515.5.5 RainWind Induced Vibrations of Stay Cables 1525.5.6 Assessment 152

    5.6 Damage Identification and Localization 1535.6.1 Motivation for SHM 1545.6.2 Current Practice 1555.6.3 Condition and Damage Indices 1575.6.4 Basic Philosophy of SHM 159

    5.7 Damage Prognosis 1615.7.1 Sensing Developments 1625.7.2 Data Interrogation Procedure for Damage Prognosis 1625.7.3 Predictive Modelling of Damage Evolution 163

    5.8 Animation and the Modal Assurance Criterion (MAC) 1645.8.1 Representation of the Calculated Mode Shapes 1645.8.2 General Requirements 1645.8.3 Correlation of Measurement and

    Calculation (MAC) 1645.8.4 Varying Number of Eigenvectors 1655.8.5 Complex Eigenvector Measurement 1655.8.6 Selection of Suitable Check Points using the MAC 166

    5.9 Ambient Vibration Derivatives (AVD) 1685.9.1 Aerodynamic Derivatives 1685.9.2 Applications of the AVM 1685.9.3 Practical Implementation 169

    References 170

    6 THEORETICAL BASES 173

    6.1 General Survey on the Dynamic Calculation Method 1746.2 Short Description of Analytical Modal Analysis 176

    viii Contents

  • 6.3 Equation of Motion of Linear Structures 1786.3.1 SDOF System 1786.3.2 MDOF System 1796.3.3 Influence of Damping 181

    6.4 Dynamic Calculation Method for the AVM 1816.5 Practical Evaluation of Measurements 181

    6.5.1 Eigenfrequencies 1816.5.2 Mode Shapes 1836.5.3 Damping 185

    6.6 Theory on Cable Force Determination 1856.6.1 Frequencies of Cables as a Function of the

    Inherent Tensile Force 1856.6.2 Influence of the Bending Stiffness 1906.6.3 Influence of the Support Conditions 1926.6.4 Comparison of the Defined Cases with

    Experimental Results 1936.6.5 Measurement Data Adjustment for Exact Cable

    Force Determination 1976.7 Transfer Functions Analysis 199

    6.7.1 Mathematical Backgrounds 1996.7.2 Transfer Functions in the Vibration Analysis 2056.7.3 Applications (Examples) 214

    6.8 Stochastic Subspace Identification 2226.8.1 Stochastic State-Space Models 2236.8.2 Stochastic System Identification 226

    References 232

    7 OUTLOOK 235

    7.1 Decision Support Systems 2367.2 Sensor Technology and Sensor Networks 236

    7.2.1 State-of-the-Art Sensor Technology 2367.3 Research Gaps and Opportunities 2377.4 International Collaboration 239

    7.4.1 Collaboration Framework 2397.4.2 Activities 243

    8 EXAMPLES FOR APPLICATION 245

    8.1 Aitertal Bridge, Post-tensional T-beam (1956) 2458.2 Donaustadt Bridge, Cable-Stayed Bridge in Steel (1996) 2488.3 F9 Viaduct Donnergraben, Continuous Box

    Girder (1979) 2508.4 Europa Bridge, Continuous Steel Box Girder (1961) 252

    Contents ix

  • 8.5 Gasthofalm Bridge, Composite Bridge (1979) 2568.6 Kao Ping Hsi Bridge, Cable-Stayed Bridge (2000) 2588.7 Inn Bridge Roppen, Concrete Bridge (1936) 2608.8 Slope Bridge Saag, Bridge Rehabilitation (1998) 2638.9 Flyover St Marx, Permanent Monitoring 2658.10 Mur Bridge in St Michael, Bridge Rehabilitation 2708.11 Rosen Bridge in Tulln, Concrete Cable-Stayed

    Bridge (1995) 2728.12 VOEST Bridge, Steel Cable-Stayed Bridge (1966) 2758.13 Taichung Bridge, Cable-Stayed Bridge 279

    APPENDIX 283

    Nomenclature 283

    INDEX 289

    x Contents

  • Preface

    The development of methods for the monitoring and assessment of structureswas driven by the demand for better as well as cheaper methods. Constraintslike undisturbed traffic flow, limited access possibilities and finally limited oreven shrinking budgets have led to a development to an assessment model wellfitted to the construction sector. Ambient vibration means that the input is notfully known, leaving, as always, a margin of uncertainty. If we accept that thesenew technologies will in certain cases not provide exact or acceptable answersour expectations on the outcome will be fulfilled. It also has to be consideredthat this early development has explored only a minor portion of its entiretechnical range, leaving much still to do. It is most likely that the one or theother of the current approaches will be overruled by future research work.Nevertheless the conception proposed for data acquisition has been made inorder to support any new technological development in the next 50 years.Even if the methodology changes, the old data will still be usable for thenew assessment routines. These facts imply that further research work shouldbe put into this subject. The sheer number of researchers working in thisfield makes us optimistic that in 10 years time a complete revision of this bookwill be due.

    Another aspect which has arisen during our work on this subject, whichwe would like to share with the reader, is that the best results have alsobeen achieved in combination with engineering judgement. The variety ofapproaches and assumptions which can be made create the potential for a widerange of misapplications, which should be avoided and might create disap-pointment for the users. The rules defined in this book are well suited tostandard cases, but the engineer who applies them also has to be aware thatthere are limitations.

    It is easy to be caught by the fascinating opportunities ambient vibrationmonitoring provides. At the same time it is very often forgotten that the effortput in also limits the potential. The dilemma that perfect results are too

  • expensive and budget approaches are limited in certain aspects has to beunderstood by all concerned parties.

    The authors wish everyone applying these methodologies great success andthe possibility to share the experience. In order to help to carry out ambientvibration monitoring activities the Green-Eye software is offered free of charge tointerested parties. It can be downloaded from the website http://www.brimos.comtogether with a set of raw data for trial application. The software is designed fordata handling and provides the basic features of frequency analysis for ambientvibration monitoring.

    xii Preface

  • Acknowledgements

    The advice, support and understanding of fellows, colleagues and family mem-bers is required to write a book. The authors are well aware that without thishelp it would not have been possible to complete it. Many of the examplespresented have been taken from actual assessment work performed during thepast years. We would like to particularly acknowledge the opportunities givento us by our clients ASAG Innsbruck (Mr. Fink), OSAG Linz (Mr. Ritzberger),MA29 Vienna (Mr. Winter), NOLR (Mr. Talmann), TLR (Mr. Aschaber),KTLR (Mr. Hawranek) and OBB (Mr. Glatzl).

    Many thanks go to our fellows of the board for their understanding, namelyMr. Peter Fritsch, Mr. Gerd Chiari, Mr. Reinhard Mechtler, Mr. HaraldSchmidt, Mr. Christian Eckerstorfer, Mr. Walter Nemeth and Mr. RobertSchedler. Among the many work contributions we would like to highlightthe input from external experts of the technical university of Leuven namelyProf. Guido DeRoeck, Mr. Bart Peters and Mrs. Anne Theugels. The work ofYozo Fujino, Dan Frangopol and Emin Aktan also inspired the developmentdescribed here. Among the many in-house contributors and co-workers wewould like to mention Mrs. Bianca Mick and in alphabetic order Mr. ErnstForstner, Mr. Peter Furtner, Mr. Roman Geier, Mr. Konstantin Savov,Mr. Martin Stoger and Mr. Robert Veit for their work.

    This publication would not have been possible without the existence ofa number of research projects. In particular the European projects IMAC-Integrated Monitoring and Assessment of Cables (G1RD-CT-2002-09003)and SAMCO-Structural Assessment Monitoring and Control (G1RT-CT-2001-05040) supported works cited here. The Austrian research projectsBRIMOS (supported by FFF-Forschung Forderungs Fond der gewerblichenWirtschaft) and the research project supported by the Ministry of Infrastructure(Dr. Gunter Breyer) enabled a development which provided the basis for thispublication.