FULL-SCALE DYNAMIC PERFORMANCE TESTING OF THE BRIDGE
STRUCTURE AND THE SPECIAL CABLE FRICTION DAMPERS ON THE
CABLE-STAYED UDDEVALLA BRIDGE
Frank Myrvoll and Amir M. Kaynia
Division of Monitoring and Division of Analysis, Norwegian Geotechnical Institute
P. O. Box 3930 Ullevaal Stadion, N-0806 Oslo, Norway
Erik Hjorth-Hansen and Einar Strømmen
Department of Structural Engineering, Norwegian University of Science and Technology
N-7491 Trondheim, Norway
ABSTRACT
(NTNU) co-ordinated the complete full-scale loading test
programme.
The cable-stayed part of the Uddevalla Bridge has a main
span of 414 m and two side spans of 179 m. The bridge was
completed May 2000 and is located on the west-coast of
Sweden in an area with relatively windy climate combined
with rain and snow. As part of the design a comprehensive
study of cable vibration and methods for passive damping
were made, and the bridge was consequently equipped with
special friction dampers on the cable-stays. In order to verify
the design and the actual performance of the dampers on the
cables and of the bridge structure itself, a series of dynamic
full-scale loading tests were made using instrumentation for
automatic monitoring of wind, temperature, accelerations,
displacements and forces.
This paper presents the
performance testing procedures, the instrumentation
techniques and selected results of the data analyses.
Comparisons are made with predictions made in design.
1
Emphasis is given in this paper to procedures for the fullscale dynamic loading tests and applied instrumentation
techniques. Typical results of the field measurements during
the performance tests are presented and compared to design
predictions as also given where possible. The tests described
herein are part of a more comprehensive performance testing
programme covering both static and dynamic full-scale
loading tests [1].
INTRODUCTION
Since the Uddevalla cable-stayed bridge has a relative long
span and large slenderness, it is a dynamically sensitive
structure subjected to random load environments in the
windy coastal region of south west Sweden, often combined
with rain or snow.
Therefore as part of the design a comprehensive study was
carried out of dynamic behaviour of the bridge and in
particular of the cable vibrations and methods for passive
damping. Consequently this bridge was equipped with
specially designed dry friction dampers on the cable stays.
In order to verify the design assumptions and to provide
information about the actual full-scale performance of the
bridge, the owner (Swedish National Road Administration)
and the structural design engineer for the bridge, (Johs. Holt
A.S), planned for a series of full-scale loading tests and
related field measurement programme at the end of the
construction period in April 2000. Norwegian Geotechnical
Institute (NGI) was contracted to carry out the field
measurements and data analyses. NGI together with its
partner Norwegian University of Science and Technology
Figure 1: Uddevalla Bridge
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In general a better understanding of the actual full-scale
performance of the structure will undoubtedly contribute to a
safer operation of the Uddevalla Bridge and, hopefully, lower
maintenance and operational costs as well, but also to
improved design of similar bridges in the future.
2
THE BRIDGE
The Uddevalla Bridge, Figure 1, is located on the west-coast
of Sweden in the windy region north of Gothenburg. The
high-level bridge of total length 1712 m was opened for traffic
in May 2000 as part a new highway between Oslo in Norway
and Malmö in the southern part of Sweden. The central
cable-stayed part with a 414 m main span and two side
spans of 179 m, constitute a relatively large span and large
slenderness. The three cable-stay spans are supported by a
total of 120 cables of the VSL type connected directly to web
of the 1.7 m high longitudinal girders. Each cable is equipped
with a specially designed dry friction damper at the lower
anchorage. The main bridge deck is a composite structure of
an open steel grid and prefabricated concrete elements
which are spanning longitudinally between cross girders
having a centre distance of 4.44 m. The two towers are
diamond-shaped concrete frames of height 137 m and 119 m
respectively.
The bridge was constructed by Skanska AB. A more
complete description of the bridge and the design and
construction work is given by the structural design engineer
[2].
3
3.1 Wind effect investigations
The wind climate at the bridge site is not particularly severe.
The 10-minute average wind speed at bridge deck level is
32.8 m/s and the turbulence intensity 14.7%. The above
values are characteristic for a return period of 100 years,
relevant for the completed bridge. For the construction
period, a return period of 10 years was adopted.
Wind tunnels tests on sectional models were performed to
determine the aerodynamic stability, the sensibility to vortex
shedding and the aerodynamic force coefficients. The tests
comprised of the following model configurations:
The completed bridge without traffic
The completed bridge with traffic
The construction stage.
According to the project specification for traffic comfort, the
2
RMS of the vertical acceleration should be less than 0.3 m/s
for frequencies lower than 1 Hz at a 10-minute wind speed of
25 m/s at bridge deck level. Also this criterion was fulfilled.
The Norwegian University of Science and Technology carried
out the wind tunnel investigations in co-operation with Svend
Ole Hansen ApS, Copenhagen.
The results of the wind tunnel testing have been used as
basis for a series of buffeting response analyses. These
analyses covered the completed bridge with and without
traffic and several critical stages during construction. Results
of the theoretical predictions of eigen-frequencies and mode
shapes for the bridge vibration are summarised in Table 2.
3.2 Cable vibration study
The problem of cable vibrations was addressed early in the
design and a comprehensive study of the problem and
methods of passive damping were carried out covering the
following structural modelling steps:
•
•
DESIGN DEVELOPMENT
As part of the conceptual and detail design the dynamic
effects of wind loads on the bridge and cable vibrations were
thoroughly investigated [2,3].
•
•
•
The sectional model was tested both in laminar and turbulent
flow. The test results confirmed that the stability criterion of
53 m/s was achieved with an ample margin. Drag, lift and
pitching moment coefficients were obtained over a range of
angles of attack.
•
•
Undamped structural eigen-frequencies and -modes
were determined for a linearized, ”global” computational
model without concern for internal modes in the staycables
In the next step, each cable-stay (including attachments
to the deck and possible damper) was modelled as an
independent sub-structure having internal degrees of
freedom in the plane normal to the chord. The theory is
described in [4].
The two simplified cases above gave sufficient material
for a rough sorting of the possibilities of parametric
effects caused by cable end-point displacements.
Finally, the response of the cables was studied
assuming that the motion of the cable support points
was well enough predicted by wind buffeting theory
using the ”global” discretization mentioned in the first
entry above.
The results showed that vibrations, either coming from wind,
possibly in combination with rain or snow, or parametric
excitation, could occur. Consequently, it was decided to
equip all cables with a specially designed friction damper
installed between the stay cable and the support pipe
extending from the lower anchorage at the bridge deck,
Figure 2. As far as we know the dry friction damper is a novel
design originally developed by Dr. Imre Kovacs [4].
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Cable
ae
Friction damper
position
Protection
tube
Extension tube
net=0
net>0
net<0
Stationary
point
Anchor beam
0
Cable head
Y0
Bridge deck
Figure 2: Left: Principle drawing of anchorage; right: theoretical prediction of damping ratio vs. modal midspan displacement
amplitude
4
TESTING PROCEDURE AND FIELD MEASUREMENT
PROGRAMME
The principal objective of the dynamic part of the tests was to
monitor the full-scale performance of the bridge and the
friction dampers when subjected to dynamic load excitation
and induced cable vibrations respectively in order to verify
design predictions.
The field measurement programme during the tests should
primarily provide information about the global behaviour of
the cable-stayed bridge itself and quantify the damping
provided by the dry friction dampers to the cable-stays.
4.1 Dynamic loading test
The bridge superstructure was excited by pulling down the
west edge of the bridge deck at mid point section with an
applied load of 46 tons (451.4 kN) using a heavy barge
beneath the bridge as counterweight. The additional
deflection of the bridge edge at the point of the applied load
was measured to be 62 mm. Subsequently, the pull-down
load was suddenly released to set the bridge structure in free
vibration, and accelerations at different locations of the
superstructure were measured.
More specifically, the objectives of the field measurements
were first of all to determine the eigen-frequencies of the first
vertical and torsional vibration modes and if possible, to
identify the first horizontal eigen-frequency of vibration.
Secondly the measurements should obtain information about
structural damping of the superstructure related to the
various modes.
4.2 Cable vibration test
The cables selected for testing were both in the central span
of the bridge in the south-western fan and identified as Cable
215 V (West), being the longest, and Cable 210 V (West),
which is the sixth longest. The cables were pulled manually
at their midpoint at a relevant eigen-frequency in both
horizontal and vertical directions for transient testing. This
cable vibration testing was carried out without the friction
damper in operation, with the friction damper set in
operational friction position according to the design
specification (friction force F=3.5 kN for cable 210 V) and at
last with the damper in operation with other friction settings.
More details on the cables selected for testing and the testing
programme are described by Hjorth-Hansen et al. [3]
The more specific objective of the field measurements during
the cable vibration tests was to verify the predicted efficiency
of the friction dampers.
4.3 Instrumentation and data acquisition system
All instrumentation was located in the main cable-stayed
span of the bridge as shown on Figure 3. A total of 23
electrical sensors for automatic data acquisition and another
34 measuring points were taken on the bridge during the
tests.
A brief description of the instrumentation concepts and data
acquisition system is outlined below. Table 1 summarises the
pertinent details of the instrumentation systems used both
during the dynamic and the static part of the full-scale
performance test programme.
The instrument used for measurement of wind speed and
directions was an acoustic anemometer from Gill. Air
temperature was measured with a resistance thermometer
and a separate autonomous logger.
The load in the stays was measured using the VSL tension
jack for hydraulic controlled tension in each strand of the
different stays.
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Measurement type and location of instruments
No. of measurement
points
Wind speed and direction at mid point of bridge.
Three components anemometer, 6.4 m above deck
Air temperature at mid point of deck.
Sensor 6.4 m above deck
Load in cable-stay.
Cable nos. 215V, 214V, 215V and 214H
Deflection of measurement points along top of west and east deck girder
and displacement of measurement points at top of the two towers
Acceleration of deck in Z- and Y- direction.
Single axis sensor at mid point and ¼ point
Acceleration of deck around X-axis.
Angular sensor at mid point and ¼ point
o
Acceleration of cable-stays in 45 plane from Y-direction.
Single axis sensors at mid point of 210V and 215V
Displacements of support pipe for cable anchorage relative to deck.
Single axis sensor at cable deck anchorage, 210V and 215V
Displacement of cable stays in two directions relative to support pipe.
Single axis sensors at cable deck anchorage 210V and 215V
Table 1:
1x3
1
1x4
1x34
2x3
2x1
2x2
2x1
2x2
Type of
Instrument
Ultrasonic
anemometer
Resistance
sensor
Hydraulic load cell
Optical precision
surveying system
Linear servo
accelerometer
Angular servo
accelerometer
Linear servo
accelerometer
Laser displacement
sensor
Laser displacement
sensor
Instrumentation details
An optical surveying system was used during the dynamic
load test of the bridge for direct monitoring of pull-down
displacement of the midspan. The Leica Wild TCA 1800
system employed is a commercially available optical levelling
and position surveying system consisting of a transmitter and
receiver unit which measures the position and the distance
for an infra red beam transmitted and reflected on an optical
target at each measuring point.
High precision linear servo accelerometers from Allied
Signal/Sundstrand Data were used to determine the dynamic
movements of the bridge deck and the cable-stays
respectively. Dynamic displacements were determined by
integrating the measured accelerations twice. Angular
accelerations were also measured separately on the bridge
deck and integrated to determine rotations. This was done
Figure 3.
using high precision angular servo accelerometers from BEI
Systron Donner.
High precision laser optical sensors from Danish Sensor
Engineering were used for measurements of displacements
at the lower end of the cable stays on the friction damping
device.
A 32 channel Racal Heim A160 DAT recorder was used to
record the sensor signals. It has a signal/noise ratio better
than 90 dB, and uses a 64 times oversampling technique in
conjunction with a simple analogue RC circuit to avoid
aliasing problems. The digital low pass filter has a ripple
smaller than 0.01dB in the passband and attenuation better
than -90 dB in the stop band. Phase errors are less than 0.1
%.
Instrumentation scheme
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possible to identify the third vertical mode (i.e. the second
symmetric mode). However, the second vertical mode, which
is anti-symmetric, was not well excited and hence not
identifiable with the symmetric loading employed for the test.
0.04
1st.vertical
0.035
0.03
3rd vertical
0.025
0.02
The identified eigen-frequencies correspond well with the
calculated theoretical values except for the horizontal mode
which has an approximately 14 % lower measured eigenvalue. The difference is believed to be partly due to the
theoretical modelling of the deck support at the towers
assumed fully fixed in horizontal direction. In the real
structure, however, some horizontal motions take place due
to lateral motion
0.015
0.01
0.005
0
0.2
3
x 10
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
Vertical acceleration at mid span
-3
2.5
2
1.5
Unfiltered, Filtered, Envelope and Damping Ratio of Vertical Acceleration: 1st Mode
0.2
Unfiltered (m/s2)
1st horizontal
1
0.5
1.6
0.3
x 10
-3
0.4
0.5
0.6
0.7
0.8
Horizontal acceleration at midspan
0.9
1
1.1
1st torsional
1.4
-0.2
1.2
1
0.6
0.1
Envelopes (m/s2)
-0.1
0.4
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Torsional acceleration at midspan
1
1.1
All measurements made in the field using the automatic data
acquisition system were sampled at 450 Hz and stored on a
digital recorder. The data was also transferred digitally to a
laptop computer in the field after each test and was saved for
further processing and analyses.
Damping ratio (%)
Figure 4: Measured eigen-requencies from power density
spectra compared with theoretical predictions
(marked with arrows)
5
100
200
300
400
Time (s)
500
600
700
0
100
200
300
400
500
600
700
0
100
200
300
400
500
600
700
0
0.8
0
0.2
0
0.1
Filtered (m/s2)
0
0.2
0
0
-0.1
0.4
0.2
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Amplitude (m/s2)
Figure 5: Damping ratio for first vertical vibration mode.
of the supports, which result in lower vibrations as measured
in that direction.
TYPICAL RESULTS OF FIELD MEASUREMENT
A thorough discussion of the field measurement data and
performance of the instrumentation with respect to recorded
behaviour of the bridge [1,3] is not possible in this paper.
However, typical results for the different measurement
systems are presented in this section for the loading tests
and are compared with design predictions where possible.
5.1 Interpreted eigen-frequencies and damping factors of
bridge suberstructure
The measured damping ratios during the test, as given in
Figure 5 and Table 2, are rather small compared to what
were theoretically assumed in the design, in particular for the
first vertical and torsional mode of vibrations and the third
vertical mode. The measurements show increasing trends of
damping ratios with higher amplitudes. It should, however,
be mentioned that the vibration amplitudes during the test
were rather small compared to the levels assumed during the
design.
The identified eigen-frequencies during free vibration test are
presented in Figure 4 and in Table 2.
The first vertical, torsional and horizontal vibration modes are
identified from the field measurements. In addition, it was
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Vibration mode
First vertical
First horizontal
First torsional
Third vertical
Range of vibration
amplitudes
6.5-23.0 mm
0.13-0.4 mm
(1.3-5.7) 10-3 deg
1.25-3.0 mm
Eigen-frequency
Measured (Hz)
0.281
0.338
0.679
0.548
Damping ratio (%) Eigen-frequency
Theoretical (Hz)
0.2-0.26
0.264
0.3-0.5
0.394
0.1-0.15
0.686
0.1-0.14
0.535
Table 2. Measured damping ratio and measured eigen-frequencies compared with theoretical predictions
5.2 Efficiency of friction dampers for cable stays
REFERENCES
Figure 6 shows a summary of interpreted damping ratios
from different cable vibration tests for cable 210 V. As shown
on the figure the field measurements during the full-scale
tests with this cable have in all respect confirmed that the
installed dry friction damper performs as predicted according
to theoretical calculations during the design phase and
contributes with great efficiency to suppress induced
vibrations of the cables.
[1] Myrvoll F. Uddevalla Bridge.– Performance Testing,
Field Measurements. Results of Static and Dynamic
Loading Tests and Cable Vibration Test. Norwegian
Geotechnical Institute, Project Report 20001141-1, June
2000.
[2] Hansvold C., Lundh L., Larsson K.-E. & Nilsson H.,
Uddevalla cable-stayed bridge. Balkema, Rotterdam,
th
Proceedings 4 Symposium on Strait Crossings, Bergen,
September 2001
[3] Hjorth-Hansen E., Strømmen E., Myrvoll F., Hansvold
C. & Ronnebrant R., Performance of a friction damping
device for the cables on Uddevalla cable-stayed bridge,
A.I.M.
Liege,
Proceedings
Fourth
International
Symposium on Cable Dynamics, Montreal, May 2001
[4] Kovacs I., Strømmen E. and Hjorth-Hansen E.,
Damping devices against cable oscillations on
Sunningesund Bridge, A.I.M., Liege, Proceedings Third
International Symposium on Cable Dynamics, pp. 145150. 1999.
Figure 6: Measured and theoretical damping ratio for
cable 210 V.
6
CONCLUDING REMARKS
The findings from the field performance testing and
instrumentation of the Uddevalla cable-stayed bridge have
contributed significantly to verifying the predictions made
during the theoretical design work.
The bridge owner is now making plans for a subsequent
additional long-term performance monitoring programme for
this bridge that shall contribute to a more effective
maintenance and safer operation, as well as to improved
design of similar bridges in the future.
ACKNOWLEDGEMENTS
The authors wish to thank Mr Lars Lundh and Mr Robert
Ronnebrant of the Swedish National Road Administration
and Mr Carl Hansvold form Design Engineers Johs Holt AS
for support and permission for publishing the results of this
project.
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