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IowaIowa’’s Highs High--Mast Lighting Towers: Mast Lighting
Towers: A Proactive Approach to a ProblemA Proactive Approach to a
Problem
Bruce BrakkeIowa Department of Transportation
Terry J. Wipf, Brent M. Phares, Byung-Ik
Chang
Iowa State University
Robert J. ConnorLehigh University
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The ProblemThe ProblemThe Problem
Nationwide failures of HMLT.Inadequate design specifications
based upon dissimilar structures.
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Iowa DOT BackgroundIowa DOT BackgroundIowa DOT Background
233 High-Mast Towers.Statewideinspection in 2000.
140 ft tower failed near Sioux City in 2003 –
Fracture in base plate weld (37 mph NW wind).
Subsequent statewide inspection–
Other cracks found.
Presenter�Presentation Notes�Photos would be helpful�
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Iowa DOT BackgroundIowa DOT BackgroundIowa DOT
BackgroundInvestigation by Dexter andothers – speculated wind
induced fatigueSeveral different retrofitsdeveloped and are
currentlybeing implementedDetermined that further investigation
needed to fully understand the problem (e.g., monitoring
needed).
Presenter�Presentation Notes�Lehigh and Wiss, Janney�
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Questions to be AnsweredQuestions to be AnsweredQuestions to be
Answered
Design for vortex shedding–
Mode(s) of vibration.
–
Loading profile.–
Wind/pole interaction characteristics
»
Roughness length (z).»
Lift coefficient (CL
).
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Questions to be AnsweredQuestions to be AnsweredQuestions to be
Answered
Design for gusting–
Mode(s) of vibration.
–
Loading profile.–
Wind/pole interaction characteristics
»
Roughness length (z).»
Coefficient of drag (CD
).
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Overall GoalOverall GoalOverall Goal
Develop a comprehensive long-term inspection and maintenance
program.Add to the body of knowledge related to the design of
slender high-mast structures.
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Monitoring System -
GeneralMonitoring System Monitoring System --
GeneralGeneral
Two poles being monitored.Hardware–
Two dataloggers.
–
Long-range wireless.–
Satellite communications.
–
24x7 data collection »
With triggering –
specified wind speeds.»
Rainflow
stress cycle counting.»
1 minute averages calculated on “the fly”.
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Monitoring System –
Pole 1Monitoring System Monitoring System ––
Pole 1Pole 1
14 strain gages.4 accelerometers.1 video camera.1
anemometer–
Wind speed.
–
Wind direction.
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Monitoring System –
Pole 2Monitoring System Monitoring System ––
Pole 2Pole 2
6 strain gages.3 anemometers–
Wind speed.
–
Wind direction.
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Video
InternetAnemometer
33 ft
Satellite
Transceiver
UPS
Data Storage Server
115.8’
14 Strain gages
4 Accelerometers
45.3’
148’
10 ft
Modem
Wireless Router
CR9000C
WAP (Bridge)
CR5000WAP
(Bridge)
B E C
5.8’
148’
6 Strain gages
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Data ProcessingData ProcessingData Processing
Extract RMS and average wind speed, stress range, and
acceleration (1 minute).Vibration information.Basic wind rose
information (speed/direction)–
Daily.
–
Monthly.–
Seasonally.
–
Yearly.
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Sample ResultsSample ResultsSample Results
Cumulative Wind Information Chart Since 2004-October1 2 3 4 5 6
7 8 9 10 11 12 13 14 15 16N NNE NE ENE E ESE SE SSE S SSW SW WSE W
WNW NW NNW
219.75 242.25 264.75 287.25 309.75 332.25 354.75 17.25 39.75
62.25 84.75 107.25 129.75 152.25 174.75 197.25231 253.5 276 298.5
321 343.5 6 28.5 51 73.5 96 118.5 141 163.5 186 208.5
Min Max 242.25 264.75 287.25 309.75 332.25 354.75 17.25 39.75
62.25 84.75 107.25 129.75 152.25 174.75 197.25 219.75 Sum %0 5 625
423 508 664 742 451 938 693 590 541 374 586 741 927 736 737 10276
12.35 10 1495 1286 1286 975 1285 961 3765 2921 1958 1226 907 1777
2225 3212 2815 1680 29774 35.510 15 1043 845 578 734 996 488 3727
3148 1531 945 1072 938 890 1803 3683 1615 24036 28.715 20 737 537
256 457 1124 292 2214 1550 555 504 400 367 280 678 2413 1176 13540
16.120 25 218 188 120 71 271 101 976 600 172 89 198 106 11 104 1190
363 4778 5.725 30 40 2 8 14 35 10 121 316 10 17 42 4 2 25 470 25
1141 1.430 35 1 2 2 1 3 1 3 78 0 0 20 0 0 1 160 1 273 0.335 40 0 0
0 0 0 0 0 20 0 0 1 0 0 0 30 0 51 0.140 45 0 0 0 0 0 0 0 9 0 0 0 0 0
0 0 0 9 0.045 50 0 0 0 0 0 0 0 7 0 0 0 0 0 0 0 0 7 0.050 100 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0
4159 3283 2758 2916 4456 2304 11744 9342 4816 3322 3014 3778
4149 6750 11497 5597 83885 100% 5.0 3.9 3.3 3.5 5.3 2.7 14.0 11.1
5.7 4.0 3.6 4.5 4.9 8.0 13.7 6.7 100 64%
Sum
Dir. No.
Speed
0
5
10
15
20N
NNE
NE
ENE
E
ESE
SE
SSE
S
SSW
SW
WSE
W
WNW
NW
NNW
% of Frequency
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0
3000
6000
9000
12000
15000
N NNE NE ENE E ESE SE SSE S SSW SW WSE W WNW NW NNWWind
direction
Win
d di
rect
ion
freq
uenc
y
50 ~ 100 mph
45 ~ 50 mph
40 ~ 45 mph
35 ~40 mph
30 ~ 35 mph
25 ~30 mph
20 ~ 25 mph
15 ~20 mph
10 ~15 mph
5 ~ 10 mph
0 ~ 5 mph
Sample ResultsSample ResultsSample Results
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S+60 Wind
0.0
2.0
4.0
6.0
8.0
10.0
0 10 20 30 40 501 min. mean wind speed (mph)
Peak
stre
ss (k
si)
S10
S12
S13
S14
Sample ResultsSample ResultsSample Results
S10
S12
S13
S14
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Sample ResultsSample ResultsSample Results
Mode 2: Frequency = 1.3 HzVortex Shedding
0
30
60
90
Time
Win
d di
rect
ion Wind direction
17.3 degree / 4.42 degree
0
10
20
30
Time
Win
d Sp
eed
Wind Speed
5.25mph / 0.47 mph
S1-S12
S2-S14
S4-S13S3-S10
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
1/17/0519:01
1/17/0519:01
1/17/0519:01
1/17/0519:01
1/17/0519:01
1/17/0519:01
1/17/0519:01
1/17/0519:02
1/17/0519:02
Time
Stre
ss (k
si)
S43.25 ksi
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
1/17/0519:01
1/17/0519:01
1/17/0519:01
1/17/0519:01
1/17/0519:01
1/17/0519:01
1/17/0519:01
1/17/0519:02
1/17/0519:02
Time
Stre
ss (k
si)
S10
Mode 2: Frequency = =1.3 Hz 3.22 ksi
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Findings –
GustingFindings Findings ––
GustingGusting
Response primarily in first mode (f 1= 0.3Hz).Overall, largest
stress ranges are caused by natural wind gusts.Max stress range is
approximately 14 ksi.Relatively few cycles–
“Slow”
vibration.
–
High wind speeds are not very frequent.
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Findings –
Vortex SheddingFindings Findings ––
Vortex SheddingVortex Shedding
Significant vortex shedding observed in the second mode (f2 =
1.3 Hz)Occurs during steady wind speeds of 4 - 11 mph (but,
somewhat dependent upon wind direction).Stress range = 1.5 ~ 3.3
ksiMaximum stress range caused by vortex shedding is approximately
3.3 ksi.Relatively high number of cycles–
“Fast”
vibration.–
Low wind speeds more common.
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Future WorkFuture WorkFuture Work
Wind tunnel testing–
Scale models to validate field CD
, CL
.–
Wind profile pressure information.
Analytical modeling–
Validated with field/wind tunnel data.
–
Extrapolate to nationwide pole geometries.Develop proposed
specification modifications.
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AcknowledgementAcknowledgementAcknowledgement
Iowa Highway Research Board.Midwest Transportation Center.
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Thank YouThank You
Questions?
Iowa’s High-Mast Lighting Towers: A Proactive Approach to a
ProblemThe ProblemIowa DOT BackgroundIowa DOT BackgroundQuestions
to be AnsweredQuestions to be AnsweredOverall GoalMonitoring System
- GeneralMonitoring System – Pole 1Monitoring System – Pole 2 Data
ProcessingSample ResultsSample ResultsSample ResultsSample
ResultsFindings – GustingFindings – Vortex SheddingFuture
WorkAcknowledgementThank You