Seismic Instrumentation of Structures: What Have We Learned?

Mehmet Çelebi, Earthquake Hazards Team, Menlo Park, CA.

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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

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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

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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.

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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:

http://www.strongmotioncenter.org • Private Owners (e.g. Banks, Industry )

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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]

and CGS(CSMIP) Program [Updated 2012] (info compiled from various CGS

publications & http://strongmotioncenter.org]

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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!).

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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]

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ITEM 1 LONG PERIOD LONG DISTANCE

EFFECTS & IMPLICATIONS Japanese Data from Tohoku (3/11/2011)

M=9.0 event

TWO CASES: Building A: ~770 km from epicenter

Building B:~350-375 km from epicenter

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 (http://earthquake.usgs.gov/earthquakes/states/events/1952_07_21.php)

• 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).

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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 (http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/se082311a/#summary, July 15, 2011).

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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)

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Building A; in Osaka Bay ~770 Km from epicenter of March 11, 2011 main-shock

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• 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

• 60-70 m long piles below foundation

The building & instrumentation

(sparse)

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Closest Free-Field Station: OSKH02 (KIK_NET) Record indicates [(a) site frequency from actual data (~.14-.18 Hz) & (b) shaking duration]

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Site Info from OSKH02 and building site indicate similarities [resulting in similar site frequency transfer function] and also similar to that from strong shaking data (previous slide] [f(site)~0.13-0.17 Hz]. Also expected to be similar to freq of 55 story bldg..RESONANCE!

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ACCELERATIONS RECORDED

(MAIN-SHOCK) Note long duration

of record and strong shaking

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ACCELERATIONS &

DISPLACEMENTS AT 52ND FLOOR

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Amplitude Spectra and Spectral Ratio

(w.r.t 1st Floor) Note: fbldg~fsite

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System Identification

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Design Analyses, Spectral Analyses & System Identification [NOTE: LOW DAMPING!!]

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AVERAGE DRIFT RATIO

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• Why average drift ratio? • Sparse instruments • ~.005 (or ~.5%) drift ratio

(X-Dir) • Implications(!!): 3%g

input motion, ~.5% drift ratio: not-acceptable

Building A:CONCLUSIONS AND REMEDIES

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• 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)

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 is 5.2 and 6.2 seconds in two perpendicular directions. The dampers were calculated to have reduced the maximum accelerations by 30% and roof displacement by 22% “.

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 building

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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

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

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]

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What is the risk to tall buildings from earthquakes

originating at NMSZ or Charleston, SC or Cascadia Subduction Zone? Should we consider what may happen to

tall buildings in Chicago, New York, Boston or Seattle?

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Tall Buildings in Chicago, Boston and Seattle

• How will they perform during a strong event from distant sources??? [pictures from Wikipedia]

According to Wikipedia: In Chicago: 72 bldgs taller than 555ft (168 m) [37-108] stories In Boston :27 buildings taller than 400 feet (120 m). “ In Seattle, 15 buildings >400 ft(122m), 24 buildings>400 ft under constrruction

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ITEM 2 SUCCESSES OF STRUCTURAL

DYNAMICS MODIFICATION FEATURES (in light of data from Tohoku earthquake)

(a) Base-isolated

(b) Dampers

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

In the USA (best data to date from): USC_BASE ISOLATED HOSPITAL

[from CGS network]

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(0.21 g)

(0.49 g)

(0.13 g)

(0.37g)

THE RECORDS RETRIEVEDFROM THE BASE-ISOLATED USCHOSPITAL [LARGEST ACCELERATIONSAND DISPLACEMENTS EXPERIENCED,TO DATE, FOR A BASE-ISOLATED BUILDING]CONFIRMED THE EFFECTIVENESS OFBASE-ISOLATION TECHNIQUES

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PERFORMANCE OF BASE-ISOLATED USC HOSPITAL DURING THE NORTHRIDGE EQ.: AT DESIGN LEVEL EQ., ONLY 10% OF DISPLACEMENT CAPACITY OF ISOLATORS REACHED. NO DAMAGE

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]

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Base-isolated buildings (Tohoku Event M=9)

(b) 9-story bldg in Sendai

(c)Comparison Non-base

isolated and base isolated

buildings

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[d](Sendai MT BLDG-isolators & dampers) 74 m (18 floors) (from Sinozaki)

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7500

〃〃

〃〃

〃〃

〃〃

〃〃

〃〃

〃〃

3950

3750

3750

2000

2050

18FL

17FL

16FL

15FL

14FL

13FL

12FL

11FL

10FL

B2FL

9FL

8FL

7FL

6FL

5FL

4FL

3FL

2FL

1FL

RFLPH1FL

B1FL

免震層床

11430

▽軒高

74900

420

2750

935

▽

PH2FL

PH2RFL

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設計GL GL平均 120

39504080

5875

▽

▽

▽

▽

▽

▽

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▽

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9980

最高高さ

2011.3.11　東北地方太平洋沖地震X [NS]方向

(cm/s2)

Y [EW]方向

(cm/s2)

Z [UD]方向

(cm/s2)

計測震度

18階床 193.8 188.6 329.910階床 156.9 155.0 215.31階床 173.0 142.9 210.8

免震ピット 310.8 225.8 206.8 5.3

0 100 200 300 4000

2

4

6

8

10

12

14

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18X [ NS] 方向

2011年東北地方太平洋沖2005年宮城県沖

最大加速度（ cm/s2）

階数

TOKYO (Yoyogi-Seminar Bldg; isolators and brace-damper (from Sinozaki) [partial active-control ]

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▽B1F ▽B2F ▽B3F

▽17F

▽26F

▽ 3F

▽10F

③Base-isolation Layer

②Control Computer

①Monitoring Sensor

①Monitoring

Sensor

①Monitoring Sensor

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 features

reduced responses significantly to result in excellent performance of the buildings.

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ITEM 3 NEW DEVELOPMENTS:

REAL-TIME MONITORING USING IP (INTERNET PROTOCOL) :

Using masured data from accelerometers &

computing displacements and drift ratios in near real-time

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• 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.

THE PROBLEM:

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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).

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New Developments: Displacement via Real-time Double Integration

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NEW TRENDS

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Development and Application (Celebi and others, 2004)

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Such developments are useful – to assess & make informed decisions!

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Sample “Small” Earthquake Response Data: San Simeon Earthquake of 12/3/03

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)

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CONCLUSIONS [what we learned?]:

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• 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.

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

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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

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

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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 Decomposition Ambient Frequency Brincker R, et al., 2000

Enhanced Frequency Domain Decomposition Ambient Frequency Brincker R, et al., 2001

Random Decrement Technique Ambient Time Asmussen JC, 1997

Stochastic Subspace Identification Ambient Time van Overschee P, and Moor BD, 1993

Eigensystem Realization Algorithm + Natural Excitation

Technique Ambient Time Juang JN, and Pappa RS, 1985

James G, et al., 1995

OTHER EXAMPLES Summary of System Identification Methods (from R. Omrani, 2012)

Method Domain Model Identified Features Data

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) ERA-DC

ERA-OKID Time State Space System Matrices

IO w/ IE OO 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 Filter Identification (Juang et al., 1985, 1988, 1993)

(5) Numerical Algorithm for Subspace State Space System Identification (N4SID) (Van Overschee & De Moor, 1994)

EXAMPLE: One Rincon Tower: Building Info

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• 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

ONE RINCON TOWER (SF): RECENTLY COMPLETED COOPERATIVE

PROJECT BETWEEN CGS (CSMIP) and USGS (TSD) Tuned Sloshing Dampers and BRB(Buckling Restrained Dampers -

also known as unbonded diagonal bracing)

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From MKA document

BRB

TSD

One Rincon Tower: Structural Monitoring System (www.strongmotioncenter.org)

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Accelerations (cm/s/s) [Data: July 2, 2012]

Displacements (cm) [Data: July 2, 2012]

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Spectral Analyses of Ambient data (6/4/2012)from One

Rincon Tower

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MODE SHAPES, FREQUENCIES, DAMPING (Data Set: 6/4/2012)

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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!

Millikan Library from E. Taciroglu(2012)

[attributed to J. Clinton (2006)

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In addition: Low-amplitude vs strong shaking Pacific Park Plaza from Çelebi, 2009

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)

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Seismic and Structural Health Monitoring in British Columbia,

Canada

UBC Earthquake Engineering

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

Background

Bridge Seismic Engineering

MOT Post Earthquake Response

What is damaged – how bad? Staffing Inspections Route condition

Prioritization Changing plans Risks/decisions

•Fast, accurate field intelligence •Speed of initial response •Effective risk assessment and decision making

What does MOT need?

Collaboration between UBC and MOT Bridge Seismic Engineering

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.

Smart Infrastructure Monitoring 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; and

2. 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.

Smart Infrastructure Monitoring 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.

Bridge Seismic Engineering

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

www.bcsims.ca

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

Current and Future Works

THANK YOU! Q?

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Remember Virginia Eq (Mw=5.8) August 23, 2011:

No deaths. Few injured. Felt in 21 states. National Cathedral and Washington Monument damaged

What do we remember about 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).

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PERFORMANCE OF BASE-ISOLATED USC HOSPITAL DURING THE NORTHRIDGE EQ.

THE RECORDS RETRIEVEDFROM THE BASE-ISOLATED USCHOSPITAL [LARGEST ACCELERATIONSAND DISPLACEMENTS EXPERIENCED,TO DATE, FOR A BASE-ISOLATED BUILDING]CONFIRMED THE EFFECTIVENESS OFBASE-ISOLATION TECHNIQUES