Ambient Vibration Monitoring

Dr Helmut Wenzel, Managing DirectorDieter Pichler, both of VCE Holding GmbH, Vienna, Austria

• PREFACE xiACKNOWLEDGEMENTS xiiiSUMMARY xv1 INTRODUCTION 11.1 Scope of Applications 11.2 Laws and Regulations 21.3 Theories on the Development of the AVM 42 OBJECTIVES OF APPLICATIONS 72.1 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 132.2 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 152.3 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 212.4 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 272.5 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 352.6 Application of Ambient Vibration Testing to Structures for Railways 352.6.1 Sleepers 362.6.2 Noise and Vibration Problems 392.7 Limitations 492.7.1 Limits of Measuring Technology 492.7.2 Limits of Application 512.7.3 Limits of Analysis 522.7.4 Perspectives 53References 543 FEEDBACK FROM MONITORING TO BRIDGE DESIGN 553.1 Economic Background 553.2 Lessons Learned 563.2.1 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 663.2.7 Damping Values of New Composite Bridges 683.2.8 Value of Patterns 683.2.9 Understanding of Behaviour 723.2.10 Dynamic Factors 72References 754 PRACTICAL MEASURING METHODS 774.1 Execution of Measuring 784.1.1 Test Planning 834.1.2 Levelling of the Sensors 834.1.3 Measuring the Structure 844.2 Dynamic Analysis 844.2.1 Calculation Models 844.2.2 State of the Art 884.3 Measuring System 894.3.1 BRIMOS_ 894.3.2 Sensors 904.3.3 Data-Logger 914.3.4 Additional Measuring Devices and Methods 924.4 Environmental Influence 934.5 Calibration and Reliability 964.6 Remaining Operational Lifetime 974.6.1 Rainflow Algorithm 984.6.2 Calculation of Stresses by FEM 1014.6.3 S–N Approach and Damage Accumulation 1044.6.4 Remaining Service Lifetime by Means of Existing Traffic Data and Additional Forward and Backward Extrapolation 1054.6.5 Conclusions and Future Work 106References 1095 PRACTICAL EVALUATION METHODS 1115.1 Plausibility of Raw Data 1115.2 AVM Analysis 1125.2.1 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 1235.2.8 Vibration Coefficients 1255.2.9 Counting of Events 1265.3 Stochastic Subspace Identification Method 1295.3.1 The Stochastic Subspace Identification (SSI) Method 1295.3.2 Application to Bridge Z24 1305.4 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 1475.5 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 Rain–Wind Induced Vibrations of Stay Cables 1525.5.6 Assessment 1525.6 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 1595.7 Damage Prognosis 1615.7.1 Sensing Developments 1625.7.2 Data Interrogation Procedure for Damage Prognosis 1625.7.3 Predictive Modelling of Damage Evolution 1635.8 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 1665.9 Ambient Vibration Derivatives (AVD_) 1685.9.1 Aerodynamic Derivatives 1685.9.2 Applications of the AVM 1685.9.3 Practical Implementation 169References 1706 THEORETICAL BASES 1736.1 General Survey on the Dynamic Calculation Method 1746.2 Short Description of Analytical Modal Analysis 1766.3 Equation of Motion of Linear Structures 1786.3.1 SDOF System 1786.3.2 MDOF System 1796.3.3 Influence of Damping 1816.4 Dynamic Calculation Method for the AVM 1816.5 Practical Evaluation of Measurements 1816.5.1 Eigenfrequencies 1816.5.2 Mode Shapes 1836.5.3 Damping 1856.6 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 1996.7.1 Mathematical Backgrounds 1996.7.2 Transfer Functions in the Vibration Analysis 2056.7.3 Applications (Examples) 2146.8 Stochastic Subspace Identification 2226.8.1 Stochastic State-Space Models 2236.8.2 Stochastic System Identification 226References 2327 OUTLOOK 2357.1 Decision Support Systems 2367.2 Sensor Technology and Sensor Networks 2367.2.1 State-of-the-Art Sensor Technology 2367.3 Research Gaps and Opportunities 2377.4 International Collaboration 2397.4.1 Collaboration Framework 2397.4.2 Activities 2438 EXAMPLES FOR APPLICATION 2458.1 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) 2528.5 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 279APPENDIX 283Nomenclature 283INDEX 289