NCHRP --IDEA Project 141: Signal Head Vibration …sp.bridges.transportation.org/Documents/2013...
Transcript of NCHRP --IDEA Project 141: Signal Head Vibration …sp.bridges.transportation.org/Documents/2013...
Reducing Fatigue in Traffic Signal Reducing Fatigue in Traffic Signal
Support Structures through the use Support Structures through the use
of a Signal Head Vibration Absorberof a Signal Head Vibration Absorber
NCHRPNCHRP--IDEA Project 141: Signal Head IDEA Project 141: Signal Head
Advanced Hazards Mitigation Lab Advanced Hazards Mitigation Lab –– Civil EngineeringCivil Engineering
NCHRPNCHRP--IDEA Project 141: Signal Head IDEA Project 141: Signal Head
Vibration AbsorberVibration Absorber
Richard ChristensonRichard Christenson
Associate ProfessorAssociate Professor
University of ConnecticutUniversity of Connecticut
NCHRPNCHRP--IDEA Project 141IDEA Project 141
“Reducing Fatigue in Wind-Excited Traffic
Signal Support Structures using Smart
Damping Techniques”
Objective: Develop and demonstrate the use
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Objective: Develop and demonstrate the use
of a signal head vibration absorber (SHVA)
to reduce fatigue in traffic signal support
structures exposed to wind excitation.
FixedFixed
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SHVASHVA
NCHRPNCHRP--IDEA Project 141IDEA Project 141
Reduce acceleration from 0.5 g to 0.06 g
(~3.5”-0.4”) in 2.75 sec (from 300 sec)
Increase damping from 0.2% to 10.1%.
98% reduction in steady state vibrations
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98% reduction in steady state vibrations
Damped Vibration AbsorberDamped Vibration Absorber
Modeling the traffic pole as a single-degree-
of-freedom (sdof) spring-mass system
x k
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x
m
k
x
m
k=1ω
mm
k
∆+=2ω
mm ∆−
=2
1
2
2
2
2
ωω
ω
2
1ωmk =
Damped Vibration AbsorberDamped Vibration Absorber
Consider the addition of a small spring-mass-
damper (ka, ma , ca ) system to the larger
structural system (k, m)
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m
k
x
caka
ma xa
),sin()( tFxkxkkxcxcxm oaaaaaa ω=−++−+ &&&&
0=+−+− aaaaaaaa xkxkxcxcxm &&&&
Damped Vibration AbsorberDamped Vibration Absorber
We are interested in a solution of the forced
vibration – dynamic amplification
( ) ( )( ) ( ) ( )( ) 222
22222 λγζλ −+
=X
X
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( ) ( ) ( )( ) 2222222221112 λµγλγλλµζλ −−−++−
=stX
== mma /µ
== aan mk /2
ω
==Ω mkn /2
=Ω= na /ωλ
== nωωγ /
== KPx ost /
=Ω= )2/( nmcζ
Mass ratio= Absorber mass/Main mass
Natural frequency of absorber
Natural frequency of main system
Frequency ratio
Forced frequency ratio
Static deflection of system
critical damping
Damped Vibration AbsorberDamped Vibration Absorber
Plotting the dynamic amplification shows there are
two points independent of damping (P and Q)
ζζζζ=0
ζζζζ=∞
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P
Q
ζζζζ=0
Damped Vibration AbsorberDamped Vibration Absorber
1. Optimal absorber freq. adjust amplitude of P & Q
to equal heights (Den Hartog)
The magnitude of P & Q is
µλ
+=
1
1
µ/211 +=X
X
=Ω= na /ωλ Frequency ratio
== mma /µ Mass ratio
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2. Optimal damping is to adjust the slope of the curve
to zero at P & Q (Seto)
In practice choose the average of the two values
( ) optζµ
µζ =
+=
318
3
µ/21 +=stX
=Ω= )2/( nmcζ critical damping
Damped Vibration AbsorberDamped Vibration Absorber
ζζζζ=0 ζζζζ=∞
Consider the 35’ traffic signal support structure
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P Q
ζζζζ=0.70
ζζζζ=0.085ζζζζ=0.05
ζζζζ=0.01
ζζζζ=0.20
Previous Mitigation DevicesPrevious Mitigation Devices
An effective vibration mitigation device can
decrease the amplitude and number of cycles,
extending the service life of these structures.
A number of other types of mitigation devices
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A number of other types of mitigation devices
have been proposed previously (McManus et
al. 2003; Cook et al. 1998; Hamilton et al.
2000; Pulipaka et al., 1998)
Type of
Dampers
Variation % Critical
damping
% Increase Disadvantage
Tuned
mass
damper
Traditional 8.71 32 Different natural
frequency requires
separate tuningStockbridge 0.42 1.5
Batten 1.82 6.7
Liquid
damper
Horizontal 0.38 1.4 Ineffective
U- tube 0.40 1.5
Friction
damper
6.49 23.9 Unattractive
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damper
Elastome
ric pads
Pad at mast arm 0.28 1.9 Ineffective
Pad at mast arm and
base
0.43 2.9
Pad at base 0.39 2.6
Strut 2.4-6.0 16-40Requires luminary
extension
Contd.
Type of
Dampers
Variation % Critical
damping
% Increase Disadvantage
Tuned
mass
damper
Traditional 8.71 32 Different natural
frequency requires
separate tuningStockbridge 0.42 1.5
Batten 1.82 6.7
Liquid
damper
Horizontal 0.38 1.4 Ineffective
U- tube 0.40 1.5
Friction
damper
6.49 23.9 Unattractive
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damper
Elastome
ric pads
Pad at mast arm 0.28 1.9 Ineffective
Pad at mast arm and
base
0.43 2.9
Pad at base 0.39 2.6
Strut 2.4-6.0 16-40Requires luminary
extension
Contd.
Dampers Variation % Critical
damping
% Increase Disadvantage
Impact
dampers
Vertical Spring/mass
impact dampers
6.79 25 High cost
Spring/mass liquid
impact dampers
6.12 22.5 High cost
Hapco Impact
damper
0.31 2.1 Ineffective
Flat –bar impact
damper
0.3-0.37 2.0-2.5 Ineffective
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dampers damper
Shot-Put impact
damper:
0.20-0.29 1.3-1.9 Ineffective
Strand impact
damper
0.97-1.4 6.5-9.3 Large size and
noise
Alcoa Dumbbell
damper
0.26 1.7 Ineffective
Dampers Variation % Critical
damping
% Increase Disadvantage
Impact
dampers
Vertical Spring/mass
impact dampers
6.79 25 High cost
Spring/mass liquid
impact dampers
6.12 22.5 High cost
Hapco Impact
damper
0.31 2.1 Ineffective
Flat –bar impact
damper
0.3-0.37 2.0-2.5 Ineffective
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dampers damper
Shot-Put impact
damper:
0.20-0.29 1.3-1.9 Ineffective
Strand impact
damper
0.97-1.4 6.5-9.3 Large size and
noise
Alcoa Dumbbell
damper
0.26 1.7 Ineffective
Signal Head Vibration AbsorberSignal Head Vibration Absorber
• In the original SHVA configuration
the moving mass, ma, is the signal
head itself, suspended by a spring
and an employing eddy current
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and an employing eddy current
damper
• The original SHVA fits inside of the
signal head
Signal Head Vibration AbsorberSignal Head Vibration Absorber
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SpringSpring
The spring rate is equal to 4.12 lb/inch with a free length of 15”
Maximum solid length of 3.3”
The spring has outside diameter of 3.25”
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of 3.25”
Made of 0.187" thick stainless steel wire
ρ
2bdBtC
c o=
Eddy Current DamperEddy Current Damper
Eddy Current Damper (Seto 1979)
c= damping coefficient (N s/m)
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c= damping coefficient (N s/m)
ρ= peculiar resistance (Ω m)
Co= modification co efficient
bd= area of magnetic flux (m2)
B= magnetic –flux density (T)
t= thickness of conductor
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NCHRPNCHRP--IDEA Project 141IDEA Project 141
Completed (January 2011)
Final report available: http://onlinepubs.trb.org/onlinepubs/idea/
finalreports/highway/NCHRP141_Final_Report.pdf
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finalreports/highway/NCHRP141_Final_Report.pdf
Short video describing SHVA: mms://159.247.0.209/mediapoint/Uconn/
NCHRP_Idea_141_v4.wmv
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Continued StudiesContinued Studies
Quantify and understand the robustness of a
SHVA performance to mistuning
Redesign SHVA based on feedback
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Redesign SHVA based on feedback
Field testing in actual wind conditions
Continued StudiesContinued Studies
Quantify and understand the robustness of a
SHVA performance to mistuning
Redesign SHVA based on feedback
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Redesign SHVA based on feedback
Field testing in actual wind conditions
Robustness of SHVARobustness of SHVA
SHVA based on principles of tuned mass damper – required to be tuned (frequency) to the dynamic property of main structure.
Individual tuning may not be practical, yet frequency of traffic signal supports range from
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Individual tuning may not be practical, yet frequency of traffic signal supports range from 0.7 Hz to 1.4 Hz.
Performance of a single SHVA applied to 2 dynamically dissimilar traffic signal support structures is examined
Two traffic poles erected in the laboratory
35 foot mast arm 55 foot mast arm
Dissimilar StructuresDissimilar Structures
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Two traffic poles erected in the laboratory
35 foot mast arm 55 foot mast arm
Dissimilar StructuresDissimilar Structures
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Dynamic Characteristics
ωωωω1 = 1.1 Hzξ= 0.2%
Meff = 229 lbs
Dynamic Characteristics
ωωωω1 = 0.8 Hzξ= 0.2%
Meff = 263 lbs
Movable Member
Test SetupTest Setup
accelerometersstrain sensors
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Effective Mass of Structure
RobustnessRobustness
• Mass and damping effects not only optimal
performance but robustness to mistuning
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95
100
Perc
ent R
eduction (
contr
olle
d v
s u
ncontr
olle
d)
RobustnessRobustness
• Mass and damping effects not only optimal
performance but robustness to mistuning
m = 70 lbs
m = 100 lbs
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0.8 1 1.2 1.4 1.6 1.8 275
80
85
90
Frequency of Mast Arm (Hz)
Perc
ent R
eduction (
contr
olle
d v
s u
ncontr
olle
d)
m = 10 lbs
m = 30 lbs
m = 50 lbs
m = 70 lbs
RobustnessRobustness
• Mass and damping effects not only optimal
performance but robustness to mistuning
80
90
100
Perc
ent R
eduction (
contr
olle
d v
s. uncontr
olle
d)
ξξξξ = 5%
ξξξξ = 10%
ξξξξ = 20%
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0.8 1 1.2 1.4 1.6 1.8 2
30
40
50
60
70
Frequency of Mast Arm (Hz)
Perc
ent R
eduction (
contr
olle
d v
s. uncontr
olle
d)
ξξξξ = 0.2%
ξξξξ = 1%
ξξξξ = 5%
RobustnessRobustness
• Mass and damping effects not only optimal
performance but robustness to mistuning
• SHVA has both
– large mass of the movable member (30-100 lbs);
and
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and
– effective damping of the eddy current damper
(durable, low maintenance, small & large
amplitude)
Experimental EvaluationExperimental Evaluation
• To simulate wind excitation a linear shaker
used to apply sinusoidal force at mast arm tip
– weight is 13 lbs
– sine wave (±2 cm, 0-5 Hz)
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– sine wave (±2 cm, 0-5 Hz)
Experimental EvaluationExperimental Evaluation
• To simulate wind excitation a linear shaker
used to apply sinusoidal force at mast arm tip
– weight is 13 lbs
– sine wave (±2 cm, 0-5 Hz)
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– sine wave (±2 cm, 0-5 Hz)
• BDI STS-WiFi system to
measure and collect
strain and accel. data
Peak acceleration decreased
from 1.42 to 0.21 m/s2
35’ 35’ Tip Tip Acceleration ResponseAcceleration Response
85% 85%
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85% 85%
stiction in bearings
Peak strain decreased
from 68 µε to 9.7 µε
35’ 35’ Strain Strain ResponseResponse
86% 86%
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86% 86%
Increase Damping from 0.2 to 9.6% of critical
35’ 35’ Tip Tip Acceleration ResponseAcceleration Response
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Peak acceleration decreased
from 2.2 to 0.4 m/s2
555’ 5’ Tip Tip Acceleration ResponseAcceleration Response
82% 82%
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82% 82%
stiction in bearings
Peak strain decreased
from 61 µε to 12 µε
555’ 5’ Strain Strain ResponseResponse
80% 80%
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80% 80%
Increase Damping from 0.2 to 6.8% of critical
555’ 5’ Tip Tip Acceleration ResponseAcceleration Response
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RobustnessRobustness
• A single SHVA can effectively reduce vibration
in both a 35 ft and 55 ft long mast arm
– relatively large additional mass
– effective damping
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• Stiction in bearings can limit performance
• A single SHVA can be used to effectively
mitigate the wind induced vibration of
multiple traffic signal support structures
reducing acceleration and strain by >80%
Continued StudiesContinued Studies
Quantify and understand the robustness of a
SHVA performance to mistuning
Redesign SHVA based on feedback
Advanced Hazards Mitigation Lab Advanced Hazards Mitigation Lab –– Civil EngineeringCivil Engineering
Redesign SHVA based on feedback
Field testing in actual wind conditions
Continued StudiesContinued Studies
Quantify and understand the robustness of a
SHVA performance to mistuning
Redesign SHVA based on feedback
Advanced Hazards Mitigation Lab Advanced Hazards Mitigation Lab –– Civil EngineeringCivil Engineering
Redesign SHVA based on feedback
Field testing in actual wind conditions
Redesigned DeviceRedesigned Device
New design to remove spring and damper
from inside signal head to outside
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Signal Head Vibration AbsorberSignal Head Vibration Absorber
• In the new SHVA configuration the
moving mass, ma, is the signal
head itself, suspended by springs
inside of the two rails and
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inside of the two rails and
employing eddy current dampers
at the 4 bearings
• The SHVA fits between available
signal brackets and the signal head
Signal Head Vibration AbsorberSignal Head Vibration Absorber
Counterweights used to reduce
friction in bearings to
accommodate different signal
head configurations
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head configurations
Extension of design to 5-head
and horizontal signal head
configurations
Signal Head Vibration AbsorberSignal Head Vibration Absorber
Laboratory tests on 35’ mast arm validate
performance
Impulse response provides information on
steady state response
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steady state response
Signal Head Vibration AbsorberSignal Head Vibration Absorber
ξξξξ = 0.25%
Laboratory tests on 35’ mast arm validate
performance (0.2% to 5%)
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ξξξξ = 0.25%
ξξξξ = 5%
Continued StudiesContinued Studies
Quantify and understand the robustness of a
SHVA performance to mistuning
Redesign SHVA based on feedback
Advanced Hazards Mitigation Lab Advanced Hazards Mitigation Lab –– Civil EngineeringCivil Engineering
Redesign SHVA based on feedback
Field testing in actual wind conditions
Continued StudiesContinued Studies
Quantify and understand the robustness of a
SHVA performance to mistuning
Redesign SHVA based on feedback
Advanced Hazards Mitigation Lab Advanced Hazards Mitigation Lab –– Civil EngineeringCivil Engineering
Redesign SHVA based on feedback
Field testing in actual wind conditions
Field Testing in ConnecticutField Testing in Connecticut
Manchester, Connecticut
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Field Testing in ConnecticutField Testing in Connecticut
Manchester, Connecticut – August 2012
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Field Testing in ConnecticutField Testing in Connecticut
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Free vibration tests show damping increased
from 0.2% to 8.5%
Field Testing in ConnecticutField Testing in Connecticut
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Qualitative results from traffic camera show
pole steady relative to others at intersection
Field Testing in TexasField Testing in Texas
UConn supplement to “Development of Design
Guidelines and Mitigation Strategies for Wind-
Induced Traffic Signal Structure Vibrations” (Project
No. 0-6649), PI Delong Zuo (Texas Tech University)
Objectives:
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Objectives:
experimentally validate the SHVA for reducing
wind induced vibration; and
assist in establishment of guidelines of design
and implementation of SHVA devices on traffic
mast arms
Field Testing in TexasField Testing in Texas
October 2012 initial visit and installation of 3-head
units; January 2013 installed 5-head SHVA unit
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Field Testing in TexasField Testing in Texas
October 2012 initial visit and installation of 3-head
units; January 2013 installed 5-head SHVA unit
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ConclusionsConclusions
• NCHRP-IDEA Project 141 successfully
demonstrated performance of SHVA concept
• Mass and damping of SHVA provide
robustness to mistuning
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robustness to mistuning
• SHVA redesigned to use existing signals and
brackets with straight forward installation
• Field testing underway to verify performance
and durability of design
AcknowledgementAcknowledgement
• NCHRP-IDEA program (Project 141)
• Connecticut Department of Transportation
• Texas Department of Transportation
• Texas Tech University
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• Texas Tech University
• University of Connecticut
• Town of Manchester, CT
• Traffic Structures Subcommittee
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