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Seismic Instrumentation of Structures: What Have We Learned? - Mehmet Çelebi


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2013 EERI Annual Meeting Session: Technology for Post-Earthquake Assessment and Monitoring

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Seismic Instrumentation of Structures: What Have We Learned? - Mehmet Çelebi

  1. 1. Seismic Instrumentation of Structures: What Have We Learned?Mehmet Çelebi, Earthquake Hazards Team,Menlo Park, CA.
  2. 2. OUTLINE• Statement of Purpose• US Inventory of Instrumented Structures• What is not covered?• What is covered?[5 topics as time allows] 1. Long-period/long-distance effects (Tohoku data) 2. Effectiveness of dynamic response modification features (Tohoku data) 3. Real-time monitoring advances 4. State-of-the-art hardware/advances in softwares 5. British Columbia (Smart Infrastructure Monitoring system for Bridges)[from Carlos Ventura]• Conclusions 2
  3. 3. Simple Statement of Purpose for Structural Instrumentation The main objective of a Seismic Instrumentation Program for structural systems is to improve our understanding of the behavior and potential for damage of structures under the dynamic loads of earthquakes 3
  4. 4. As a result• design and construction practices and building codes can be improved• life and property losses can be reduced• informed decisions can be made – (a) in emergency response situations, and/or – (b) to retrofit or strengthen the structural system – (c) to secure the contents within the structures • The requirement for accomplishing this aim is to expand and upgrade the existing network of instrumented structures to record their responses during earthquakes. 4
  5. 5. Structural Monitoring Programs• State of California (CGS)-CSMIP• USGS (Cooperative Program with other agencies, local governments and organizations) – DATA & INFO FROM BOTH CGS & USGS at CESMD (Combined Engineering Strong Motion Data) web site:• Private Owners (e.g. Banks, Industry ) 5
  6. 6. Status-quo Inventory: USGS-Cooperative Structural Monitoring Program [USGS,ACOE,VA,GSA,UPR,CITY OF SF.ODAT.MWD,JPL] [note: 3 channels or more within a structure, updated Dec.20, 2012] andCGS(CSMIP) Program [Updated 2012] (info compiled from various CGS publications &] 6
  7. 7. What is NOT covered?• Use of recorded data to establish code period formulas (e.g. see Goel-Chopra papers, Willam Jacobs paper)• Successes of past analyses of recorded responses (Transamerica – Rocking identified?)• Routine methods to analyze recorded responses (f, damping, mode shapes).• Past data analyses from bridge responses (Golden Gate, Cape Girardeau Bridge)• Wireless instrumentation (still not viable!). 7
  8. 8. What is covered [5 topics]?1. Long-period/long-distance effects (Tohoku data) & what we learned!2. Effectiveness of dynamic response modification features (Tohoku data)3. Real-time monitoring advances4. State-of-the-art hardware/advances in softwares5. British Columbia (Smart Infrastructure Monitoring system for Bridges)[from Carlos Ventura] 8
  9. 9. ITEM 1 LONG PERIOD LONG DISTANCE EFFECTS & IMPLICATIONSJapanese Data from Tohoku (3/11/2011) M=9.0 event TWO CASES: Building A: ~770 km from epicenterBuilding B:~350-375 km from epicenter 9
  10. 10. Background (Long Period/Long Distance Effects) 1/2• One of the earliest observations in the United States was during the M=7.3 Kern County earthquake of July 7, 1952, that shook many taller buildings in Los Angeles and vicinity, about 100-150 km away from the epicenter (• One of the most dramatic examples of long-distance effects of earthquakes is from the September 19, 1985, Michoacan, Mexico, M 8.0 earthquake during which, at approximately 400 km from the coastal epicenter, Mexico City suffered more destruction and fatalities than the epicentral area due to amplification and resonance (mostly around 2 sec) of the lakebed areas of Mexico City (Anderson and others, 1986, Çelebi and others, 1987). 10
  11. 11. Why important?Potential Long Period/Long Distance Effects in the US (2/2)• Tall buildings in Los Angeles area from Southern California earthquakes,• Tall buildings in Chicago from NMSZ,• Tall buildings in Seattle (WA) area from large Cascadia subduction zone earthquakes).• Let us remember that the recent M=5.8 Virginia earthquake of August 23, 2011 was felt in 21 states of the Eastern and Central U.S., that include large cities such as New York and Chicago ( 11/se082311a/#summary, July 15, 2011). 11
  12. 12. What we learned from Tohoku EQ? Why important? Discussion of INTERRUPTED functionality of buildings at low ground level input motions caused by event at far distances (e.g. 770km). Possible hidden damages? Discussion of what may happen at larger input motions with similar frequency content. Discussion of DRIFT RATIOS w.r.t. codes (Japan, USA, Chile)Two cases (others are not presented): Building A (770 km from epicenter) Building B (350-375 km from epicenter) 12
  13. 13. Building A; in Osaka Bay ~770 Km from epicenter of March 11, 2011 main-shock• 256 m tall (55 stories+3 story basement)• Construction finished in 1995 (pre-1995 code, pre-(KIK-NET/K-NET). Vertically irregular, steel, moment-frame (rigid truss-beams/10 floor). No shear walls around elevator shafts 13• 60-70 m long piles below foundation
  14. 14. The building &instrumentation (sparse) 14
  15. 15. Closest Free-Field Station:OSKH02 (KIK_NET)Record indicates[(a) site frequency fromactual data (~.14-.18 Hz)& (b) shaking duration] 15
  16. 16. Site Info from OSKH02 and building siteindicate similarities [resulting in similar sitefrequency transfer function] and also similar tothat from strong shaking data (previous slide][f(site)~0.13-0.17 Hz]. Also expected to besimilar to freq of 55 story bldg..RESONANCE! 16
  17. 17. ACCELERATIONS RECORDED (MAIN-SHOCK) Note long durationof record and strong shaking 17
  19. 19. Amplitude Spectraand Spectral Ratio (w.r.t 1st Floor) Note: fbldg~fsite 19
  20. 20. System Identification 20
  21. 21. Design Analyses, Spectral Analyses & System Identification [NOTE: LOW DAMPING!!] 21
  22. 22. AVERAGE DRIFT RATIO • Why average drift ratio? • Sparse instruments • ~.005 (or ~.5%) drift ratio (X-Dir) • Implications(!!): 3%g input motion, ~.5% drift ratio: not-acceptable 22
  23. 23. Building A:CONCLUSIONS AND REMEDIES• Building lost functionality for many days due to elevator cable entanglements and other problems.• Resonance occurred and still occurs because f(building)~f(site)• Damping is too low [ambient tests could have provided some clues]• (average) Drift Ratios are high for a 3% g input motion. What if input a>.2g?• Sparse instrumentation• Implications (US): tall buildings in Chicago, NY, Boston from far sources• Structural Response Modification Technologies (being designed – see below) 23
  24. 24. Building B: 55-Story Shinjuku Center Building in Shinjuku, Tokyo (~350-375 km from Epicenter)According to EERI Special Earthquake Report (EERI Newsletter, 2012), the 54-story Shinjuku Center Building was constructed in 1979. The report states:“The structure’s height is 223m, and the first natural period of the structure is5.2 and 6.2 seconds in two perpendicular directions. The dampers werecalculated to have reduced the maximum accelerations by 30% and roofdisplacement by 22% “.
  25. 25. Building B: Shinjuku Center Building• Figure courtesy of J. Moehle and Y. Sinozaki (Taisei Corp)• Recorded first story acceleration (BLUE~max ~0.15g).• Roof level displacement time history (RED : max~54 cm) Most notable is the long duration motion over 10 minutes.• AVERAGE DRIFT RATIO: 54/21600 = ~0.25% < 1% according to Japanese practice.• However: the actual drift ratios computed from relative displacements divided by story heights between some of the pairs of two consecutive floors are certainly to be larger than the average drift ratio computed using the maximum roof displacement divided by the height of the 25 building
  26. 26. CONCLUSIONS [what we learned?] (1/2)• 1. For small ground level input ground motions as in the two cases presented herein, these two tall buildings deformed significantly to experience sizeable drift ratios.• 2. Collection of such data is essential (a) to assess the effect of long period ground motions on long period structures caused by sources at large distances, and (b) to consider these effects and discuss whether the design processes should consider reducing drift limits to more realistic percentages (c) finally, further applications of unique response modification features are feasible to reduce the drift ratios. 26
  27. 27. CONCLUSIONS [what we learned?] (2/2)• 3. Behavior and performances of these particular tall buildings far away from the strong shaking source of the M9.0 Tohoku earthquake of 2011 and large magnitude aftershocks should serve as a reminder that, in the United States as well as in many other countries, risk to such built environments from distant sources must always be considered.• 4. The risk from closer large-magnitude earthquakes that could subject the buildings to larger peak input motions (with similar frequency content) should be assessed in light of the substantial drift ratios under the low peak input motions experienced during and following the Tohoku earthquake of 2011. 27
  28. 28. DRIFT RATIO (DR): CODES• JAPAN: Max DR=1% for collapse protection level motions (level 2 used for buildings 60 m or taller [The Building Center of Japan, 2001a and 2001b]).• UNITED STATES: MAX DR=2% for tall buildings for Risk Category 1 or 2. (Table 12.12, ASCE7-10, 2007).• CHILE: MAX DR=0.2% [The Chilean Code for Earthquake Resistant Design of Buildings (NCh433.Of96, 1996) [effective since 1960’s] 28
  29. 29. What is the risk to tall buildings from earthquakes originating at NMSZ or Charleston, SC or CascadiaSubduction Zone? Should we consider what may happen to tall buildings in Chicago, New York, Boston or Seattle? 29
  30. 30. Tall Buildings in Chicago, Boston and SeattleAccording to Wikipedia: In Chicago: 72 bldgs taller than 555ft (168 m) [37-108] storiesIn Boston :27 buildings taller than 400 feet (120 m). “In Seattle, 15 buildings >400 ft(122m), 24 buildings>400 ft under constrruction• How will they perform during a strong event from distant sources??? [pictures from Wikipedia] 30
  31. 31. ITEM 2 SUCCESSES OF STRUCTURALDYNAMICS MODIFICATION FEATURES (in light of data from Tohoku earthquake) (a) Base-isolated (b) Dampers 31
  32. 32. Seismic Base-Isolation• Since 1980’s… [similar to soft first story]• US (today) 125 bldgs, ~ dozen bridges• Japan (today) 6500 bldgs and ~ 6500 bridges (from Taylor & Aiken, Structure [ASCE], March 2012 issue)• In Tokyo alone, ~1500 tall buildings, ~1000 base- isolated buildings: Performances: Excellent! 32
  33. 33. In the USA (best data to date from):USC_BASE ISOLATED HOSPITAL [from CGS network] 33
  36. 36. From Japan:Base-isolated buildings (Tohoku Event M=9) (a) 7-story bldg in Tsukuba [~350 km from epicenter] [BI: ~.33g, AI=.09g, 6th Fl=.125g] 36
  37. 37. Base-isolated buildings (Tohoku Event M=9) (b) 9-story bldg in Sendai 37
  38. 38. (c)Comparison Non-base isolated and base isolated buildings 38
  39. 39. [d](Sendai MT BLDG-isolators & dampers) 74 m (18 floors) (from Sinozaki) 2011年東北地方太平洋沖 935 ▽ 最高高さ ▽ PH2RFL 2005年宮城県沖 5875 2750 ▽ PH2FL 9980 ▽ PH1FL 4080 420 ▽ 軒高 ▽ RFL ▽ 18FL 7500 3950 〃 〃 〃 〃 〃 〃 〃 〃 〃 〃 〃 〃 〃 〃 3950 ▽ 17FL ▽ 16FL 18 X [ NS] 方向 ▽ 15FL ▽ 14FL ▽ 13FL ▽ 12FL 16 ▽ 11FL 74900 ▽ 10FL ▽ 9FL 14 ▽ 8FL ▽ 7FL ▽ 6FL 12 ▽ 5FL ▽ 4FL 10 階数 ▽ 3FL ▽ 2FL ▽ 1FL 8 120 GL ▽設計 GL ▽平均 3750 2050 ▽ 免震層床 20 3750 ▽ B1FL 11430 ▽ B2FL 2000 62011.3.11 東北地方太平洋沖地震 4 X [NS]方向 Y [EW]方向 Z [UD]方向 計測 2 (cm/s2) (cm/s2) (cm/s2) 震度 0 18階床 193.8 188.6 329.9 0 100 200 300 400 10階床 156.9 155.0 215.3 最大加速度( cm 2) /s 1階床 173.0 142.9 210.8 39免震ピット 310.8 225.8 206.8 5.3
  40. 40. TOKYO (Yoyogi-Seminar Bldg; isolators and brace-damper(from Sinozaki) [partial active-control ] ▽26F ①Monitoring Sensor ①Monitoring Sensor ▽17F ▽10F ▽ 3F▽B1F▽B2F ①Monitoring▽B3F Sensor ②Control Computer ③Base-isolation Layer 40
  41. 41. CONCLUSIONS [what we learned?]• IN US, with example of USC Hospital data during shaking at design level, and• IN JAPAN: Numerous examples with base isolation and other featuresreduced responses significantly to result inexcellent performance of the buildings. 41
  42. 42. ITEM 3 NEW DEVELOPMENTS: REAL-TIME MONITORINGUSING IP (INTERNET PROTOCOL) : Using masured data from accelerometers & computing displacements and drift ratios in near real-time 42
  43. 43. THE PROBLEM: • The owner needs reliable and timely expert advice on whether or not to occupy the building following an event. • Data gathered will enable the owner to assess the need for post- earthquake connection inspection, retrofit and repair of the building. 43
  44. 44. Drift vs. Performance• The most relevant parameter to assess performance is the measurement or computation of actual or average story drift ratios. Specifically, the drift ratios can be related to the performance- based force-deformation curve hypothetically represented in Figure 1 [modified from Figure C2-3 of FEMA-274 (ATC 1997)]. When drift ratios, as computed from relative displacements between consecutive floors, are determined from measured responses of the building, the performance and as such “damage state” of the building can be estimated as in the figure (below). 44
  45. 45. New Developments: Displacement via Real-time Double Integration 45
  46. 46. NEW TRENDS 46
  47. 47. Development and Application (Celebi and others, 2004) 47
  48. 48. Such developments are useful – toassess & make informed decisions! 48
  49. 49. Sample “Small” Earthquake Response Data: San Simeon Earthquake of 12/3/03 49
  50. 50. Commercial Versions installed at some banks [3 components: (1) sensors, (2) DAQ’s & Processors, (3) Display&Alarm system for informed decisions] (Figure from D. Sokolnik) 50
  51. 51. CONCLUSIONS [what we learned?]:• Measured data from carefully crafted monitoring are being successfully used (in US, Japan and other countries) to make informed decisions in near-real time about behavior, performance and occupancy of buildings.• Not covered here: Some bridges in Korea. 51
  52. 52. ITEM 4 NEW TECHNOLOGY & BENEFITS• Hardware (new developments)• Software (real-time technology, and developments in improved analyses methods)• Ambient Data acquisition issues & Comment about low-amplitude/strong shaking 52
  53. 53. HARDWARE (INDUSTRY STANDARD)• 24 bit almost universally available & feasable• High sampling rate (1 sps to 2000 sps): USGS (200sps) Multiple Data formats (COSMOS, EVT, SAC, MATLAB, ASCII, MiniSEED) & Telemetry Protocols (Antelope) Extensive SOH monitoring; input and system voltage, internal temp, humidity, comm link diagnostics• On-demand ambient data acquisition issues 53
  54. 54. SOFTWARE (for Analyses)• Well-known spectral analyses (auto/cross spectra, amplitude spectra, response spectra, phase and coherency analyses)• Less well-known : sophisticated system identification analyses –many new developments• Good data is essential for analyses• High sampling rate (at least 100sps, preferably 200sps)• Strong-shaking data/low-amplitude shaking data 54
  55. 55. SOME EXAMPLES : Existing Output-Only Identification Techniques (from E. Taciroglu, 2012) Technique Input Type Domain Reference Ibrahim Method Ambient Time Ibrahim SR, and Mikulcik EC, 1973 Frequency Domain Ambient Frequency Brincker R, et al., 2000 DecompositionEnhanced Frequency Domain Ambient Frequency Brincker R, et al., 2001 DecompositionRandom Decrement Technique Ambient Time Asmussen JC, 1997 Stochastic Subspace Ambient Time van Overschee P, and Moor BD, 1993 Identification Eigensystem Realization Juang JN, and Pappa RS, 1985Algorithm + Natural Excitation Ambient Time James G, et al., 1995 Technique
  56. 56. OTHER EXAMPLESSummary of System Identification Methods (from R. Omrani, 2012) Identified Method Domain Model Data Features CEM (1) Time ARMA ω, ζ IO RPEM (2) Time ARMA ω, ζ IO UMP (3) Time & Freq. ARMA ω, ζ, φ IO ERA (4) IO w/ IE ERA-DC Time State Space System Matrices OO ERA-OKID IO N4SID (5) Time State Space System Matrices IO & OO(1) Cumulative Error Minimization (Ljung, 1987)(2) Recursive Prediction Error Minimizatin (Ljung 1987)(3) Unified Matrix Polynomial (Allemang, 1994)(4) Eigensystem Realization Algorithm, w/ Data Correlations or Observer/Kalman FilterIdentification (Juang et al., 1985, 1988, 1993)(5) Numerical Algorithm for Subspace State Space System Identification (N4SID) (VanOverschee & De Moor, 1994)
  57. 57. EXAMPLE: One Rincon Tower: Building Info • Construction completed in 2008 • Designed according to 2001 SFBC • 64-story • 188.31m (617.83ft) tall • Design includes outrigger columns, and • Unique dynamic response modification features: • BRB (buckling restrained braces), and • TSD (tuned liquid sloshing Pile foundation 57
  58. 58. ONE RINCON TOWER (SF): RECENTLY COMPLETED COOPERATIVEPROJECT BETWEEN CGS (CSMIP) and USGS(TSD) Tuned Sloshing Dampers and BRB(Buckling Restrained Dampers - also known as unbonded diagonal bracing) From MKA document BRB TSD 58
  59. 59. One Rincon Tower: Structural Monitoring System ( 59
  60. 60. Accelerations (cm/s/s) [Data: July 2, 2012] 60
  61. 61. Displacements (cm) [Data: July 2, 2012] 61
  62. 62. Spectral Analyses of Ambient data (6/4/2012)from One Rincon Tower 62
  63. 63. MODE SHAPES, FREQUENCIES, DAMPING (Data Set: 6/4/2012) 63
  64. 64. CONCLUSIONS [what we learned?]:• Ambient data analyzed yields repeatable /consistent frequencies• No indication that BRB’s and TSD “kicked in” to alter dynamic characteristics• As expected low-amplitude ambient data yield periods (frequencies) that are shorter (longer) than DBE or MCE analyses which reflect larger level shaking for design• The low-amplitude shaking dynamic characteristics will serve as base-line for comparison with those that will be obtained from future strong shaking data.• This building percentage of core shear wall area/floor area compares well with those that are practiced in Chile and has performed well.• Unique design building monitoring yield high-quality data that enables extraction of at least 5 modes and associated frequencies/damping in each direction. MANY NEW SID METHODS! 64
  65. 65. In addition: Low-amplitude vs strong shaking Millikan Library Pacific Park Plaza from E. Taciroglu(2012) from Çelebi, 2009[attributed to J. Clinton (2006) 65
  66. 66. ITEM 5: Seismic and Structural Health Monitoring in British Columbia, Canada from Carlos Ventura• A new network in Canada• Data will be available openly (per C. Ventura) 66
  67. 67. UBC Earthquake EngineeringSeismic and Structural HealthMonitoring in British Columbia, Canada
  68. 68. Background The Geologic Survey of Canada maintains a strong motion network The BC Ministry of Transportation (MoT) has become involved adding many strong motion sites around the province MoT has been involved in structural monitoring since the late 1990’s, in collaboration with UBC The last 5 years has seen their integration into a comprehensive online network
  69. 69. Bridge Seismic Engineering MOT Post Earthquake Response  What is damaged – how bad?  Staffing  Inspections  Route condition  Prioritization  Changing plans  Risks/decisions What does MOT need? •Fast, accurate field intelligence •Speed of initial response •Effective risk assessment and decision making
  70. 70. A way to address concerns Have Strong Motion Network put on “the net”.  Have a GIS layer for Disaster Response Routes (DRR) & bridges  Have a GIS layer for other vital points.  Read the values affecting DRR’s/bridges  Prioritize inspection deployment.Collaboration between UBC and MOT Bridge Seismic Engineering
  71. 71. Smart InfrastructureMonitoring System (BCSIMS)The goals of this Project are to:1. develop and implement a real-time seismic structural response system to enable rapid deployment and prioritized inspections of the Ministry’s structures; and2. develop and implement a health monitoring program to address the need for safe and cost-effective operation of structures in British Columbia This system will include decision-making tools that will expedite the process of prioritization, risk assessment and damage evaluation to assist decision-makers with post earthquake response and recovery options.
  72. 72. Smart InfrastructureMonitoring System (SIMS)The objectives of this Project are to:1. develop and implement a cost-effective, reliable Structural Health Monitoring (SHM) technology that makes effective use of sensors and broad band digital communications for remote monitoring of structures subjected to dynamic loads;2. identify and implement effective algorithms for system identification, model updating and damage detection suitable for remote monitoring of structures subjected to seismic forces and condition changes due to deterioration or impact;3. develop an integrated decision support system that incorporates geographical information and information about ground shaking and structural performance of a portfolio of remotely monitored structures distributed throughout the province.
  73. 73. Seismic SHM Solution Implement damage detection algorithms to identify loss of structural integrity  Damage from impact, deterioration or seismic Provide a dense ground motion network Provide “Internet” and “local” data access and information display Provide a trigger response mechanism Instrument key bridges Bridge Seismic Engineering
  74. 74.
  75. 75. Current and Future Works Installation of updated monitoring hardware on three structures Review of monitoring systems for the new structures Implementation of existing systems into BCSIMS Deploying 20 new strong motion stations Seismic performance modelling of several bridges Further implementation of damage detection algorithms – ISMS Project Upgrading of current BCSIMS system components Work with inspectors/bridge engineers to determine best format of information, creation of operational guidelines Collaboration with other Government agencies and groups; Ministry of Education, Emergency Management BC, BC Housing, Municipalities
  76. 76. THANK YOU! Q? 81
  77. 77. 82
  78. 78. Remember Virginia Eq (Mw=5.8) August 23, 2011: No deaths. Few injured. Felt in 21 states.National Cathedral and Washington Monument damaged
  79. 79. What do we rememberabout these events most? WASHINGTON MONUMENT base 55 feet 1½ inches wide on each side (reduces to 34-feet 5⅝ inches wide at the 500- foot level).