1 Wind, Thermal, and Earthquake Monitoring of the Watts Towers Initial Results Ertugrul Taciroglu, UCLA Engineering Bob Nigbor, Jackson English, UCLA Engineering The Staff NEES at Watts Towers, 4/23/2013

Today’s Agenda  UCLA presentation of initial results  Discussion of LACMA monitoring data  UCLA’s project plan – Further monitoring, analysis & modeling  LACMA’s project plan  Discussion of how UCLA can best contribute to LACMA’s effort  Discussion of “products” NEES at Watts Towers, 4/23/2013 2

LACMA Monitoring  Custom crack & temperature monitoring system installed September 2012 with help from Harry Jones of Texas Measurements  Three cracks monitored  Weather monitoring system installed 2012? On top of site storage container NEES at Watts Towers, 4/23/2013 3

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UCLA Monitoring  Initial system installed January 30, acceleration and tilt at ~10m on main tower  Additional crack displacement (2) and wind sensor installed March 11  Crack displacement sensor power cleaned up on April 8 – now can see daily movement NEES at Watts Towers, 4/23/2013 5

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Data Description  All sensor signals sampled at 200 times/second with very high resolution digitizer  Data timing synchronized within 10 microseconds to absolute time (Universal Time coordinated (UTC), also called GMT) using GPS signals  Data recorded continuously in 1-hour blocks on local PC in LACMA trailer  Remote access possible (but slow and intermittent)through cellular broadband NEES at Watts Towers, 4/23/2013 9

Sample 1-hr Acceleration Raw Data NEES at Watts Towers, 4/23/

Sample 1-hr Raw Tilt Data NEES at Watts Towers, 4/23/

Sample 1-hr Temperature Raw Data NEES at Watts Towers, 4/23/

Initial Analysis  Quality check on all 1-hour data files  Take 1-hour averages of all data (means except root-mean-square for acceleration)  Extract dominant frequencies (“notes, fundamental & overtones”) from acceleration  Look for patterns & trends NEES at Watts Towers, 4/23/

Acceleration Analysis NEES at Watts Towers, 4/23/

NEES at Watts Towers, 4/23/ Spectrogram/Sonogram of acceleration, showing frequency (“tone”) content over 1 hour For comparison, Middle C is 262Hz, lowest piano note (double pedal A) is 28Hz

NEES at Watts Towers, 4/23/ 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/ Temperature variation of first mode/note in N-S direction

NEES at Watts Towers, 4/23/ Temperature variation of 3rd mode/note in E-W direction

Observations on Vibration Behavior  Main tower vibration behavior is simple in N-S direction but complex in E-W direction  Lowest modes/notes are 2.3Hz N-S and 2.6Hz in E-W direction  Structure is stiffer in E-W direction  Modes are quite frequency dependent, indicating a temperature dependant stiffness. NEES at Watts Towers, 4/23/

Tilt Analysis NEES at Watts Towers, 4/23/

NEES at Watts Towers, 4/23/ Sample North Tilt, 1-hour

NEES at Watts Towers, 4/23/ Sample West Tilt, 1-hour

NEES at Watts Towers, 4/23/ North Tilt and Temperature vs. Time in Hours

NEES at Watts Towers, 4/23/ North Tilt and Temperature vs. Time in Hours

Observations on Tilt Behavior  The main tower tracks the sun, leaning away from the sunny side  Daily variation.01 to.1 degree  There may be a longer trend associated with average temperature, but we’re not sure if this is a measurement artifact. More data are needed, especially from summer temperatures. NEES at Watts Towers, 4/23/

Crack Displacement/Movement Analysis NEES at Watts Towers, 4/23/

NEES at Watts Towers, 4/23/ North Crack Displacement and Temperature

NEES at Watts Towers, 4/23/ South Crack Displacement and Temperature

NEES at Watts Towers, 4/23/ Sample Daily Crack Cycling

Wind Analysis NEES at Watts Towers, 4/23/

NEES at Watts Towers, 4/23/ Looking for Wind-Related Trends in Tilt Behavior

NEES at Watts Towers, 4/23/ Looking for Wind-Related Trends in Dynamic Behavior

Observations on Crack Behavior  After the power supply was changed on 4/8 we have the resolution to measure daily variations  Crack movement correlates with temperature on a daily basis, with different behavior on the two cracks  There may be longer trends in the data, but we’re not sure if it is real or a measurement artifact  Daily movement of the north crack is about inch (0.01mm)  Daily movement of the south crack is about 0.01 inch (0.02mm) NEES at Watts Towers, 4/23/

UCLA Structure Modeling  Computer modeling not yet started  We anticipate two model types: Dynamic model to look at wind & earthquake behavior Static model to study global temperature effects NEES at Watts Towers, 4/23/

Initial Comparisons of UCLA and LACMA Data NEES at Watts Towers, 4/23/

NEES at Watts Towers, 4/23/ Temperature, LACMA & UCLA

NEES at Watts Towers, 4/23/ Wind Speed, LACMA (5-minute) & UCLA (1-hr)

NEES at Watts Towers, 4/23/ LACMA South Crack UB-5A (Displacement in mm)

NEES at Watts Towers, 4/23/ UCLA South Crack Displacement (inch)

NEES at Watts Towers, 4/23/ LACMA PI Data (Displacement in mm)

NEES at Watts Towers, 4/23/ LACMA Test Plate UB-5A Data

NEES at Watts Towers, 4/23/ LACMA Test Plate PI-2 Data

Further data needed for LACMA & UCLA crack data comparison  Get April data from LACMA for comparison with post-April 8 UCLA data  Directly compare both daily variation & long-term “drift”  Is the long-term signal real? NEES at Watts Towers, 4/23/

Earthquake Data  M4.7 near Anza on March 11, 172km from Watts Towers  M2.3 near Manhattan Beach on March 23, 16km from Watts Towers NEES at Watts Towers, 4/23/

NEES at Watts Towers, 4/23/

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Preliminary Observations Summary  Thermal effects are clear: tilt, structural frequency/stiffness, and crack movement change with temperature  Solar heating (as opposed to air temperature) may dominate tilt and crack movement  Vibrations from moderate wind and small earthquakes are much less than thermal affects NEES at Watts Towers, 4/23/

Discussion questions  Are these results useful to LACMA, and how can they be more useful to the project?  How do we validate the crack data from both LACMA & UCLA, especially the longer trends?  Thermal behavior seems to govern the movement of the structure and cracks. What can we do together to better understand this? NEES at Watts Towers, 4/23/

Today’s Agenda  UCLA presentation of initial results  Discussion of LACMA monitoring data  UCLA’s project plan – Further monitoring, analysis & modeling  LACMA’s project plan  Discussion of how UCLA can best contribute to LACMA’s effort  Discussion of “products” NEES at Watts Towers, 4/23/