Ambient Vibration Monitoring

In-operation vibration monitoring for complex mechanical structures and rotating machines is of key importance in many industrial areas such as aeronautics (wings and other structures subject to strength), automobile (gearbox mounting with a sports car body), rail transportation, power engineering (rotating machines, core and pipes of nuclear power plants), and civil engineering (large buildings subject to hurricanes or earthquakes, bridges, dams, offshore structures). Tools for the detection and the diagnosis of small changes in vibratory characteristics are particularly useful to set up a preventive maintenance policy based on the actual evolution of the state of the monitored machine or structure, as opposed to systematic a priori planning. Ambient Vibration Monitoring is the backbone of such structural assessment monitoring and control. It provides the possibility to gain useful data under ambient conditions for the assessment of structures and components. Written by a widely respected authority in this area, Ambient Vibration Monitoring describes the current practice of ambient vibration methodologies illustrated by a number of practical examples. Designed to aid the practical engineer with their understanding of the topic, it is the culmination of many years of practical research and includes numerous 'real world' examples. It also provides information on applicable solutions. This book will enable not only practitioners (in civil, mechanical and aerospace engineering), but also researchers and students, to learn more about the theory and practical applications of this subject.

Table of Contents:
PREFACE. ACKNOWLEDGEMENTS. SUMMARY. 1 INTRODUCTION. 1.1 Scope of Applications. 1.2 Laws and Regulations. 1.3 Theories on the Development of the AVM. 2 OBJECTIVES OF APPLICATIONS. 2.1 System Identification. 2.1.1 Eigenfrequencies and Mode Shapes. 2.1.2 Damping. 2.1.3 Deformations and Displacements. 2.1.4 Vibration Intensity. 2.1.5 Trend Cards. 2.2 Stress Test. 2.2.1 Determination of Static and Dynamic Stresses. 2.2.2 Determination of the Vibration Elements. 2.2.3 Stress of Individual Structural Members. 2.2.4 Determination of Forces in Tendons and Cables. 2.3 Assessment of Stresses. 2.3.1 Structural Safety. 2.3.2 Structural Member Safety. 2.3.3 Maintenance Requirements and Intervals. 2.3.4 Remaining Operational Lifetime. 2.4 Load Observation (Determination of External Influences). 2.4.1 Load Collective. 2.4.2 Stress Characteristic. 2.4.3 Verification of Load Models. 2.4.4 Determination of Environmental Influences. 2.4.5 Determination of Specific Measures. 2.4.6 Check on the Success of Rehabilitation Measures. 2.4.7 Dynamic Effects on Cables and Tendons. 2.4.8 Parametric Excitation. 2.5 Monitoring of the Condition of Structures. 2.5.1 Assessment of Individual Objects. 2.5.2 Periodic Monitoring. 2.5.3 BRIMOS- Recorder. 2.5.4 Permanent Monitoring. 2.5.5 Subsequent Measures. 2.6 Application of Ambient Vibration Testing to Structures for Railways. 2.6.1 Sleepers. 2.6.2 Noise and Vibration Problems. 2.7 Limitations. 2.7.1 Limits of Measuring Technology. 2.7.2 Limits of Application. 2.7.3 Limits of Analysis. 2.7.4 Perspectives. References. 3 FEEDBACK FROM MONITORING TO BRIDGE DESIGN. 3.1 Economic Background. 3.2 Lessons Learned. 3.2.1 Conservative Design. 3.2.2 External versus Internal Pre-stressing. 3.2.3 Influence of Temperature. 3.2.4 Displacement. 3.2.5 Large Bridges versus Small Bridges. 3.2.6 Vibration Intensities. 3.2.7 Damping Values of New Composite Bridges. 3.2.8 Value of Patterns. 3.2.9 Understanding of Behaviour. 3.2.10 Dynamic Factors. References. 4 PRACTICAL MEASURING METHODS. 4.1 Execution of Measuring. 4.1.1 Test Planning. 4.1.2 Levelling of the Sensors. 4.1.3 Measuring the Structure. 4.2 Dynamic Analysis. 4.2.1 Calculation Models. 4.2.2 State of the Art. 4.3 Measuring System. 4.3.1 BRIMOS^(r). 4.3.2 Sensors. 4.3.3 Data-Logger. 4.3.4 Additional Measuring Devices and Methods. 4.4 Environmental Influence. 4.5 Calibration and Reliability. 4.6 Remaining Operational Lifetime. 4.6.1 Rainflow Algorithm. 4.6.2 Calculation of Stresses by FEM. 4.6.3 S-N Approach and Damage Accumulation. 4.6.4 Remaining Service Lifetime by Means of Existing Traffic Data and Additional Forward and Backward Extrapolation. 4.6.5 Conclusions and Future Work. References. 5 PRACTICAL EVALUATION METHODS. 5.1 Plausibility of Raw Data. 5.2 AVM Analysis. 5.2.1 Recording. 5.2.2 Data Reduction. 5.2.3 Data Selection. 5.2.4 Frequency Analysis, ANPSD (Averaged Normalized Power Spectral Density). 5.2.5 Mode Shapes. 5.2.6 Damping. 5.2.7 Deformations. 5.2.8 Vibration Coefficients. 5.2.9 Counting of Events. 5.3 Stochastic Subspace Identification Method. 5.3.1 The Stochastic Subspace Identification (SSI) Method. 5.3.2 Application to Bridge Z24. 5.4 Use of Modal Data in Structural Health Monitoring. 5.4.1 Finite Element Model Updating Method. 5.4.2 Application to Bridge Z24. 5.4.3 Conclusions. 5.5 External Tendons and Stay Cables. 5.5.1 General Information. 5.5.2 Theoretical Bases. 5.5.3 Practical Implementation. 5.5.4 State of the Art. 5.5.5 Rain-Wind Induced Vibrations of Stay Cables. 5.5.6 Assessment. 5.6 Damage Identification and Localization. 5.6.1 Motivation for SHM. 5.6.2 Current Practice. 5.6.3 Condition and Damage Indices. 5.6.4 Basic Philosophy of SHM. 5.7 Damage Prognosis. 5.7.1 Sensing Developments. 5.7.2 Data Interrogation Procedure for Damage Prognosis. 5.7.3 Predictive Modelling of Damage Evolution. 5.8 Animation and the Modal Assurance Criterion (MAC). 5.8.1 Representation of the Calculated Mode Shapes. 5.8.2 General Requirements. 5.8.3 Correlation of Measurement and Calculation (MAC). 5.8.4 Varying Number of Eigenvectors. 5.8.5 Complex Eigenvector Measurement. 5.8.6 Selection of Suitable Check Points using the MAC. 5.9 Ambient Vibration Derivatives (AVD^(r)). 5.9.1 Aerodynamic Derivatives. 5.9.2 Applications of the AVM. 5.9.3 Practical Implementation. References. 6 THEORETICAL BASES. 6.1 General Survey on the Dynamic Calculation Method. 6.2 Short Description of Analytical Modal Analysis. 6.3 Equation of Motion of Linear Structures. 6.3.1 SDOF System. 6.3.2 MDOF System. 6.3.3 Influence of Damping. 6.4 Dynamic Calculation Method for the AVM. 6.5 Practical Evaluation of Measurements. 6.5.1 Eigenfrequencies. 6.5.2 Mode Shapes. 6.5.3 Damping. 6.6 Theory on Cable Force Determination. 6.6.1 Frequencies of Cables as a Function of the Inherent Tensile Force. 6.6.2 Influence of the Bending Stiffness. 6.6.3 Influence of the Support Conditions. 6.6.4 Comparison of the Defined Cases with Experimental Results. 6.6.5 Measurement Data Adjustment for Exact Cable Force Determination. 6.7 Transfer Functions Analysis. 6.7.1 Mathematical Backgrounds. 6.7.2 Transfer Functions in the Vibration Analysis. 6.7.3 Applications (Examples). 6.8 Stochastic Subspace Identification. 6.8.1 Stochastic State-Space Models. 6.8.2 Stochastic System Identification. References. 7 OUTLOOK. 7.1 Decision Support Systems. 7.2 Sensor Technology and Sensor Networks. 7.2.1 State-of-the-Art Sensor Technology. 7.3 Research Gaps and Opportunities. 7.4 International Collaboration. 7.4.1 Collaboration Framework. 7.4.2 Activities. 8 EXAMPLES FOR APPLICATION. 8.1 Aitertal Bridge, Post-tensional T-beam (1956). 8.2 Donaustadt Bridge, Cable-Stayed Bridge in Steel (1996). 8.3 F9 Viaduct Donnergraben, Continuous Box Girder (1979). 8.4 Europa Bridge, Continuous Steel Box Girder (1961). 8.5 Gasthofalm Bridge, Composite Bridge (1979). 8.6 Kao Ping Hsi Bridge, Cable-Stayed Bridge (2000). 8.7 Inn Bridge Roppen, Concrete Bridge (1936). 8.8 Slope Bridge Saag, Bridge Rehabilitation (1998). 8.9 Flyover St Marx, Permanent Monitoring. 8.10 Mur Bridge in St Michael, Bridge Rehabilitation. 8.11 Rosen Bridge in Tulln, Concrete Cable-Stayed Bridge (1995). 8.12 VOEST Bridge, Steel Cable-Stayed Bridge (1966). 8.13 Taichung Bridge, Cable-Stayed Bridge. APPENDIX. Nomenclature. INDEX.