Structural Health Monitoring

Size: px

Start display at page:

Download "Structural Health Monitoring"

Arron Wright
5 years ago
Views:

1 Structural Health Monitoring A overview of an evolving research area Part 2 (SHM) Bob Bolton

2 SHM Definition Damage Identification and Health Monitoring of Structural and Mechanical Systems from Changes in Their Vibration Characteristics: A Literature Review Doebling, S W, C R Farrar, et al (1996) Damage Identification and Health Monitoring of Structural and Mechanical Systems From Changes in Their Vibration Characteristics: A Literature Review, LA MS Los Alamos National Laboratory

3 SHM Definition 1996 Classification of methods A system of classification for damage-identification methods, as presented by Rytter (1993), defines four levels of damage identification, as follows: Level 1: Determination that damage is present in the structure Level 2: Determination of the geometric location of the damage Level 3: Quantification of the severity of the damage Level 4: Prediction of the remaining service life of the structure Rytter, A (1993) Vibrational Based Inspection of Civil Engineering Structures Aalborg, Denmark, University of Aalborg PhD

4 SHM Definition 1996 Damage Identification Methods Frequency Changes The Forward Problem The Inverse Problem Mode Shape Changes Mode Shape Curvature/Strain Mode Shape Changes Dynamically Measured Flexibility Comparison of Flexibility Changes Unity Check Method Stiffness Error Matrix Method Effects of Residual Flexibility Changes in Measured Stiffness Matrix Matrix Update Methods Objective Functions and Constraints Optimal Matrix Update Methods Sensitivity-Based Update Methods Eigenstructure Assignment Method Hybrid Matrix Update Methods and Other Considerations Nonlinear Methods Neural Network-Based Methods Other Methods

5 SHM Definition 2004 Definition of Damage Damage is defined as changes introduced into a system that adversely affects its current or future performance. Damage is not meaningful without a comparison between two system states, one is often an initial or undamaged state. System changes include material and/or geometric property changes, changes in boundary conditions, and changes in system connectivity. Sohn, H., C. R. Farrar, et al. (2004). A Review of Structural Health Monitoring Literature form ,. LA MS. Los Alamos National Laboratory.

6 SHM Definition 2004 Definition of Damage State The damage state of a system can be described along the lines of the levels from Rytter (1993). Questions to ask: 1. Is there damage in the system (existence)? 2. Where is the damage in the system (location)? 3. What kind of damage is present (type)? 4. How severe is the damage (extent)? 5. How much useful life remains (prognosis)?

7 SHM Definition 2004 Definition of Structural Health Monitoring Structural Health Monitoring (SHM) is the process of implementing a damage detection strategy for engineering infrastructure. Usage monitoring (UM) Measure inputs to and responses of a structure before damage so the onset of damage and deterioration can be identified. Prognosis is the coupling of information from SHM, UM, environmental and operational conditions, component and system level testing, and modeling to estimate condition and useful life.

8 SHM Definition 2004 Components of a SHM Process 1. Operational Evaluation 2. Data Acquisition, Fusion, and Cleansing 3. Feature Extraction and Information Condensation 4. Statistical-Model Development for Feature Discrimination

9 SHM Definition Operational Evaluation Topics to address: Economic and/or Life-Safety Issues Definition of Damage Environmental and/or Operational Constraints Data Management

10 SHM Definition Data Acquisition, Fusion, and Cleansing Sensing and collection issues: Excitation Methods Forced Excitation Ambient Excitation Local Excitation Data Transmission Wired Transmission Wireless Transmission Sensing Structural Response Strain Displacement Acceleration Temperature Wind Other Measurement Quantities MEMS Technology for Sensing Motion Fiber-Optic Sensors Sensor Placement Other Issues

11 SHM Definition Feature Extraction and Information Condensation Parameters and methods: Resonant Frequencies Frequency Response Functions Mode Shapes (MAC and CoMAC) Mode Shape Curvatures Modal Strain Energy Dynamic Flexibility Damping Antiresonance Ritz Vectors ARMA Family Models Canonical Variate Analysis (CVA) Nonlinear Features Time-Frequency Analysis Empirical Mode Decomposition Hilbert Transform Principal Component Analysis or Singular Value Decomposition Finite Model Updating Wave Propagation Autocorrelation Functions Other Features

12 SHM Definition Statistical-Model Development for Feature Discrimination Supervised Learning Response Surface Analysis Fisher s Discriminant Neural Networks Genetic Algorithms Support Vector Machines Unsupervised Learning Control Chart Analysis Outlier Detection Neural Networks Hypothesis Testing Other Probability Analyses Totals: 180 pages

13 SHM Definition 2004 Applications & Related information Applications Related information Aerospace - 11 papers SHM Projects - 9 projects Civil Infrastructure Web Sites - 16 sites Bridges - 30 papers Conferences - 9 conf. Buildings - 5 papers Journals 7 journals Beams - 6 papers Composites - 15 papers Others -16 papers

14 SHM State of the art 2006 Final comments from: Montalvao, D., N. M. M. Maia, et al. (2006). "A review of vibration-based structural health monitoring with special emphasis on composite materials." Shock and Vibration Digest 38(4): Many techniques exist for the identification and location of damage. No method solves all problems in all structures. Techniques have damage related sensitivities. A sensitive technique may produce false-positives. A less sensitive technique may give false-negatives. Defect size has a noise floor. Researchers are exploring multiple detection strategies. Exploration of non-linear parameters is increasing.

15 SHM State of the art 2006 Final comments from: Montalvao, D., N. M. M. Maia, et al. (2006). "A review of vibration-based structural health monitoring with special emphasis on composite materials." Shock and Vibration Digest 38(4): The quantification of damage and prediction of the remaining lifetime are the most difficult issues, particularly the latter. Most traditional detection methods are based on appreciable reductions in rigidity of a structural element Must relate reduction in rigidity to a decrease in strength or life. Prognosis must still deal with this. Statistical methods have seen considerable development in dealing with experimental errors, incompleteness, and environmental and operational conditions. Statistical pattern recognition techniques that allow for a reduction in sensors still requires considerable further work.

16 SHM State of the art 2007 Worden, K., C. R. Farrar, et al. (2007). "The fundamental axioms of structural health monitoring." Proceedings of the Royal Society of London, Series A (Mathematical, Physical and Engineering Sciences) 463(2082): Based on the extensive literature that has developed on structural health monitoring over the last 20 years, it can be argued that this field has matured to the point where several fundamental axioms, or general principles, have emerged. The intention of this paper is to explicitly state and justify these axioms. In so doing, it is hoped that two subsequent goals are facilitated. First, the statement of such axioms will give new researchers in the field a starting point that alleviates the need to review the vast amounts of literature in this field. Second, the authors hope to stimulate discussion and thought within the community regarding these axioms.

17 SHM State of the art 2007 Worden, K., C. R. Farrar, et al. (2007). "The fundamental axioms of structural health monitoring." Proceedings of the Royal Society of London, Series A (Mathematical, Physical and Engineering Sciences) 463(2082): Based on the extensive literature that has developed on structural health monitoring over the last 20 years, it can be argued that this field has matured to the point where several fundamental axioms, or general principles, have emerged. The intention of this paper is to explicitly state and justify these axioms. In so doing, it is hoped that two subsequent goals are facilitated. First, the statement of such axioms will give new researchers in the field a starting point that alleviates the need to review the vast amounts of literature in this field. Second, the authors hope to stimulate discussion and thought within the community regarding these axioms. Axiom I: All materials have inherent flaws or defects. AxiomII: The assessment of damage requires a comparison between two system states. Axiom III: Identifying the existence and location of damage can be done in an unsupervised learningmode, but identifying the type of damage present and the damage severity can generally only be done in a supervised learning mode. Axiom IVa: Sensors cannot measure damage. Feature extraction through signal processing and statistical classification is necessary to convert sensor data into damage information. Axiom IVb: Without intelligent feature extraction, the more sensitive a measurement is to damage, themore sensitive it is to changing operational and environmental conditions. Axiom V: The length- and time-scales associated with damage initiation and evolution dictate the required properties of the SHM sensing system. Axiom VI: There is a trade-off between the sensitivity to damage of an algorithm and its noise rejection capability. Axiom VII: The size of damage that can be detected from changes in system dynamics is inversely proportional to the frequency range of excitation.

18 Application Rapid Analysis/Automation Estimating dynamic properties of a stadium Ambient vibrations at the roof of a football stadium were recorded during a football game. 4 hours of acceleration data sampled at 80 Hz Complete data set analyzed in a very short time Using PolyMAX resulted in extremely clear stabilization diagrams automating parameter ID Peeters, B., H. Van Der Auweraer, et al. (2007). "Operational modal analysis for estimating the dynamic properties of a stadium structure during a football game." Shock and Vibration 14(4):

19 Application Rapid Analysis/Automation Estimating dynamic properties of a stadium

20 Application Rapid Analysis/Automation Estimating dynamic properties of a stadium Rapid reduction of data 4 seconds

21 Application Rapid Analysis/Automation Estimating dynamic properties of a stadium Comparison of PolyMAX and SSI extraction methods: PolyMAX much faster Both methods had trouble following higher modes during event

22 Application Real-time seismic monitoring Level 4 seismic monitoring system Celebi, M., A. Sanli, et al. (2004). "Real-time seismic monitoring needs of a building owner - And the solution: A cooperative effort." Earthquake Spectra 20(2): Problem: The building owner needs timely advice on whether or not to occupy the building following an event. Solution: Analysis of building response during strong-shaking event allows owner to assess possible postearthquake inspection, retrofit, and repair needs.

23 Application Real-time seismic monitoring The owner and the consultants have agreed that general building-related evaluation will commence in the building following any one of the following events: A state of emergency in the city or county of San Francisco has been declared, A M6.0 earthquake on the San Andreas or Hayward or Rodgers Creek faults, or Peak ground acceleration greater than 0.25 g (this is intended as free-field motion and adopted from Table 3-1, FEMA-352 [SAC 2000]). Level 4 seismic monitoring system

Application Real-time seismic monitoring Monitoring System Requirements The system must facilitate rapid assessment of the building integrity following an earthquake; The system must provide data

24 Application Real-time seismic monitoring Monitoring System Requirements The system must facilitate rapid assessment of the building integrity following an earthquake; The system must provide data correlated with known and building specific engineering parameters, drift ratio, related to the expected damage condition The monitoring system must deliver the data within a relatively short time (a few minutes if not in seconds). Level 4 seismic monitoring system

Application Real-time seismic monitoring Monitoring System Status Waiting for an event Producing low amplitude data in real time for analyses and

25 Application Real-time seismic monitoring Monitoring System Status Waiting for an event Producing low amplitude data in real time for analyses and assessment. System can be used for: Post event seismic assessment Trending of structural characteristics and damage Level 4 seismic monitoring system

Application GPS Bridge monitoring system Advanced technology monitoring system A real-time kinematic (RTK) global positioning system (GPS) has been developed and installed on the Humen Bridge for

26 Application GPS Bridge monitoring system Advanced technology monitoring system A real-time kinematic (RTK) global positioning system (GPS) has been developed and installed on the Humen Bridge for monitoring of bridge deck motion from: Seismic activity Traffic load Environment Temperature Wind Guo, J., L. Xu, et al. (2005). "Application of the Real-Time Kinematic Global Positioning System in Bridge Safety Monitoring." Journal of Bridge Engineering 10(2):

27 Application Advanced technology monitoring system GPS Bridge monitoring system The Humen Bridge GPS RTK on-line monitoring system is a permanent installation It includes: A RTK reference station 12 GPS monitoring stations (7 currently installed) An optical fiber communication network A control center

28 Application Advanced technology monitoring system GPS Bridge monitoring system Some measurements: Lateral Displacement vs Wind Vertical Displacement vs Temperature

29 Application GPS Bridge monitoring system Some measurements: Spectral Density Resonant Frequencies Advanced technology monitoring system

30 Application Advanced technology monitoring system GPS Bridge monitoring system Monitoring System Status Implemented GPS RTK technology provide real-time multi-point displacement measurements. Sample Rate: 1 and 20 Hz Displacement Accuracy: ±1 cm Deformation: Vertical, Lateral, Rotation Estimate characteristic frequencies Traffic management system: Alarm warns drivers when displacements are beyond critical values Torsional deck rotation during typhoon

31 Application Long-term seismic monitoring Building seismic monitoring Durand, F., J. Rogers, et al. (2004). Ambient vibration and earthquake strongmotion data sets for selected USGS extensively instrumented buildings. Open-File Report U. S. Geologic Survey, N. S. M. Program, 345 Middlefield Road, Melno Park, CA. The buildings selected for this study meet three criteria: (1) they are located in either the greater Los Angeles or San Francisco Bay areas; (2) they are extensively instrumented by the USGS; and (3) they have been strongly shaken by earthquakes with peak ground accelerations in excess of 10% of the acceleration of gravity.

32 Application Building seismic monitoring Long-term seismic monitoring Name and location of extensively instrumented buildings in the study.

33 Application Building seismic monitoring Long-term seismic monitoring Available data for three buildings. Stat. No Station Name Great Western Pacific Park Plaza Imperial Hwy City Berkeley Emeryvil le Norwalk * Currently being processed Event Date 18-Oct Oct Feb- 03 Event Name Loma Prieta Loma Prieta Lat. (deg) Long. (deg) M Dist. (km) Peak Base A (g) Peak Roof A (g) Dublin Jan-94 Northridge Oct- 87 Whittier Narrows* N/A N/A

The fourteen-story building was constructed using an proprietary lift-slab structural system, with

34 Application Building seismic monitoring Long-term seismic monitoring Former Great Western Savings Building The former Great Western Savings building was constructed in The fourteen-story building was constructed using an proprietary lift-slab structural system, with floors poured at the base of two concrete towers and then jacked into place. The building underwent a limited-scope, retrofit in 2000.

The building has a delta wing plan and several re-entrant corners at the wing ends.

35 Application Building seismic monitoring Pacific Park Plaza The thirty-story Pacific Park Plaza building in Emeryville was constructed in The lateral force resisting system is a ductile concrete moment-resisting frame. The building has a delta wing plan and several re-entrant corners at the wing ends. The building was extensively instrumented by the USGS with sensors. The structural array is complemented by freefield and bore-hole instruments. Long-term seismic monitoring

Application Building seismic monitoring Imperial Norwalk Centre The former Bechtel office building in Norwalk is now occupied by a number of local and federal law enforcement agencies.

36 Application Building seismic monitoring Imperial Norwalk Centre The former Bechtel office building in Norwalk is now occupied by a number of local and federal law enforcement agencies. The building is a 7- story steel moment-framed structure constructed in the early 1980 s. The building has an unusually high aspect ratio (>3:1) in plan, but no significant vertical or plan irregularities. The analog structural array has recorded a number of Southern California earthquakes, including the 1987 Whittier Narrows and 1994 Northridge quakes. Long-term seismic monitoring

37 Conclusions (my personal) Extremely many fields involved Spread over a wide range of applications Methods are getting mature Instrumentation is getting affordable Extreme potential It is going to be reality we think We better co-operate (a lot)

Real-Time Seismic Monitoring Needs of a Building Owner and the Solution

Real-Time Seismic Monitoring Needs of a Building Owner and the Solution by M. Çelebi 1, A. Sanli 1, M. Sinclair 2, S. Gallant 2 and D. Radulescu 3 ABSTRACT A recently implemented advanced seismic monitoring