LAX TB Presentation 11/6/07

1Wind, Thermal, and Earthquake Monitoring of the Watts Towers

Initial Results

Ertugrul Taciroglu, UCLA EngineeringBob Nigbor, NEES@UCLAJackson English, UCLA EngineeringThe NEES@UCLA Staff

NEES at Watts Towers, 4/23/2013

1Todays AgendaUCLA presentation of initial resultsDiscussion of LACMA monitoring dataUCLAs project plan Further monitoring, analysis & modelingLACMAs project planDiscussion of how UCLA can best contribute to LACMAs effortDiscussion of productsNEES at Watts Towers, 4/23/20132LACMA MonitoringCustom crack & temperature monitoring system installed September 2012 with help from Harry Jones of Texas MeasurementsThree cracks monitoredWeather monitoring system installed 2012? On top of site storage containerNEES at Watts Towers, 4/23/20133NEES at Watts Towers, 4/23/20134

UCLA MonitoringInitial system installed January 30, acceleration and tilt at ~10m on main towerAdditional crack displacement (2) and wind sensor installed March 11Crack displacement sensor power cleaned up on April 8 now can see daily movementNEES at Watts Towers, 4/23/20135NEES at Watts Towers, 4/23/20136

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Data DescriptionAll sensor signals sampled at 200 times/second with very high resolution digitizerData timing synchronized within 10 microseconds to absolute time (Universal Time coordinated (UTC), also called GMT) using GPS signalsData recorded continuously in 1-hour blocks on local PC in LACMA trailerRemote access possible (but slow and intermittent)through cellular broadband

NEES at Watts Towers, 4/23/20139Sample 1-hr AccelerationRaw DataNEES at Watts Towers, 4/23/201310

Sample 1-hr Raw Tilt DataNEES at Watts Towers, 4/23/201311

Sample 1-hr Temperature Raw DataNEES at Watts Towers, 4/23/201312

Initial AnalysisQuality check on all 1-hour data filesTake 1-hour averages of all data (means except root-mean-square for acceleration)Extract dominant frequencies (notes, fundamental & overtones) from accelerationLook for patterns & trends

NEES at Watts Towers, 4/23/201313Acceleration AnalysisNEES at Watts Towers, 4/23/201314NEES at Watts Towers, 4/23/201315

Spectrogram/Sonogram of acceleration, showing frequency (tone) content over 1 hour

For comparison, Middle C is 262Hz, lowest piano note (double pedal A) is 28HzNEES at Watts Towers, 4/23/201316

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, 4/23/201317

Temperature variation of first mode/note in N-S directionNEES at Watts Towers, 4/23/201318

Temperature variation of 3rd mode/note in E-W directionObservations on Vibration BehaviorMain tower vibration behavior is simple in N-S direction but complex in E-W directionLowest modes/notes are 2.3Hz N-S and 2.6Hz in E-W directionStructure is stiffer in E-W directionModes are quite frequency dependent, indicating a temperature dependant stiffness.NEES at Watts Towers, 4/23/201319Tilt AnalysisNEES at Watts Towers, 4/23/201320NEES at Watts Towers, 4/23/201321

Sample North Tilt, 1-hourNEES at Watts Towers, 4/23/201322

Sample West Tilt, 1-hourNEES at Watts Towers, 4/23/201323

North Tilt and Temperature vs. Time in HoursNEES at Watts Towers, 4/23/201324North Tilt and Temperature vs. Time in Hours

Observations on Tilt BehaviorThe main tower tracks the sun, leaning away from the sunny sideDaily variation .01 to .1 degreeThere may be a longer trend associated with average temperature, but were not sure if this is a measurement artifact. More data are needed, especially from summer temperatures.

NEES at Watts Towers, 4/23/201325Crack Displacement/Movement AnalysisNEES at Watts Towers, 4/23/201326NEES at Watts Towers, 4/23/201327North Crack Displacement and Temperature

NEES at Watts Towers, 4/23/201328South Crack Displacement and Temperature

NEES at Watts Towers, 4/23/201329

Sample Daily Crack CyclingWind AnalysisNEES at Watts Towers, 4/23/201330NEES at Watts Towers, 4/23/201331

Looking for Wind-Related Trends in Tilt BehaviorNEES at Watts Towers, 4/23/201332Looking for Wind-Related Trends in Dynamic Behavior

Observations on Crack BehaviorAfter the power supply was changed on 4/8 we have the resolution to measure daily variationsCrack movement correlates with temperature on a daily basis, with different behavior on the two cracksThere may be longer trends in the data, but were not sure if it is real or a measurement artifactDaily movement of the north crack is about 0.005 inch (0.01mm)Daily movement of the south crack is about 0.01 inch (0.02mm)

NEES at Watts Towers, 4/23/201333UCLA Structure ModelingComputer modeling not yet startedWe anticipate two model types:Dynamic model to look at wind & earthquake behaviorStatic model to study global temperature effects

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Initial Comparisons of UCLA and LACMA DataNEES at Watts Towers, 4/23/201335NEES at Watts Towers, 4/23/201336

Temperature, LACMA & UCLANEES at Watts Towers, 4/23/201337

Wind Speed, LACMA (5-minute) & UCLA (1-hr)NEES at Watts Towers, 4/23/201338

LACMA South Crack UB-5A (Displacement in mm)NEES at Watts Towers, 4/23/201339UCLA South Crack Displacement (inch)

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LACMA PI Data (Displacement in mm)NEES at Watts Towers, 4/23/201341LACMA Test Plate UB-5A Data

NEES at Watts Towers, 4/23/201342LACMA Test Plate PI-2 Data

Further data needed for LACMA & UCLA crack data comparisonGet April data from LACMA for comparison with post-April 8 UCLA dataDirectly compare both daily variation & long-term driftIs the long-term signal real?NEES at Watts Towers, 4/23/201343Earthquake DataM4.7 near Anza on March 11, 172km from Watts TowersM2.3 near Manhattan Beach on March 23, 16km from Watts Towers

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Preliminary Observations SummaryThermal effects are clear: tilt, structural frequency/stiffness, and crack movement change with temperatureSolar heating (as opposed to air temperature) may dominate tilt and crack movementVibrations from moderate wind and small earthquakes are much less than thermal affectsNEES at Watts Towers, 4/23/201349Discussion questionsAre 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, 4/23/201350Todays AgendaUCLA presentation of initial resultsDiscussion of LACMA monitoring dataUCLAs project plan Further monitoring, analysis & modelingLACMAs project planDiscussion of how UCLA can best contribute to LACMAs effortDiscussion of productsNEES at Watts Towers, 4/23/201351