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DISCOVERY IN THE ENGINEERING SIDE DISCOVERY IN THE ENGINEERING SIDE OF SEISMIC MONITORINGOF SEISMIC MONITORING

Bob Nigbor, NEES@UCLA

SITS 2013, Albuquerque

Discovery from data IS important in earthquake engineering.

There is much to discover about structural behavior from better measurements and more complete monitoring, including different time scales, length scales, and metrics.

Lessons learned from Earthscope, hi-res seismic exploration, and decades of continuous recording of ground motions can be applied to experimental study of the “engineering layer”

The existing strong-motion infrastructure should be leveraged to provide better measurements

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Samoa Bridge, Eureka, CA

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Accelerometer

Recording

Samoa Bridge Strong Motion Infrastructure

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Active & Passive Testing 6/6/13

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Watts Towers Monitoring

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Repair & Preservation of Watts Towers by LA County Museum of Art

What is causing cracking? Earthquakes Wind Temperature Differential temperature (sunlight)

Can dominant cause be mitigated?

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NSF-funded Monitoring by NEES@UCLA (Taciroglu PI) Acceleration Tilt (AGI, microradian precision) Temperature Static & dynamic wind Crack displacement Others in future

Continuous data recording to capture different time scales

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Acceleration & Tilt

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Dynamic Wind (5Hz)

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Crack Displacement

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Frequencies (modes) of the main tower are at 2.2, 3.7, 6.5 Hz in the N-S direction. Vibration is complex in E-W direction due to coupling with other towers.

NEES at Watts Towers, 4/23/2013 202.24

2.26

2.28

2.30

2.32

2.34

2.36

2.38

2.40

2.42

2.44

2.46

0.000

5.000

10.000

15.000

20.000

25.000

30.000

35.000

0 100 200 300 400 500 600 700 800

Freq

uenc

y (H

z)

Tem

pera

ture

(Deg

C)

Hours Since 3:00 PM - 1/31/13

Temp, Deg C

First Mode Frequency

Temperature variation of first mode in N-S direction

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North Tilt and Temperature vs. Time in Hours

-2.120

-2.100

-2.080

-2.060

-2.040

-2.020

-2.000

0.000

5.000

10.000

15.000

20.000

25.000

30.000

35.000

0 100 200 300 400 500 600 700 800 900

Temp, Deg C

Tilt (degrees)

Crack Movement

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-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.00 48.00 96.00 144.00 192.00 240.00 288.00 336.00 384.00 432.00 480.00 528.00

Sout

h Cr

ack

Disp

lace

men

t, i

nch

Time, Hours since 4/1/13 00:00 UTC

PI-2 South

UCLA Crack Data

Monitoring Discoveries So Far

4 months of monitoring shows importance of different time scales and different measurements

Thermal effects govern Strong thermal effect on stiffness

(frequency) is interesting Still waiting for earthquake & strong

Santa Ana winds

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