Typography

1
LA GESTION DES PONT SUSPENDUS - L'EXPÉRIENCE
DANNOISE A SERVICE LIFE DESIGN APPROACH TO
SUSPENSION BRIDGES
presentation by Jens Sandager Jensen Head of
Department Maintenance Rehabilitation
-Bridges, COWI A/S, Kongens Lyngby,
Denmark jes_at_cowi.dk
2
Introduction

• Suspension bridges
• Construction of suspension bridges requires huge
  investment
• Often part of strategically important
  transportation corridors
• Closure or traffic capacity reduction causes
  major inconveniences for the users and result in
  significant losses to the economy
• Often placed in very harsh environment

3
Service life design

• Challenges
• Increasing lifetime requirements up to 200
  years of service life
• Traffic has to be maintained continuously with
  less possible interruption
• Major maintenance or rehabilitation has to be
  avoided
• Approaches
• Design for durability
• Design considering Life Cycle Costs (LCC)
• Design for accessibility and maintainability

4
Content of the presentation

• Case studies
• New Little Belt Bridge, Denmark
  dehumidification system for the main girder
• Great Belt Bridge, Denmark - enhancing service
  life of movement devices, preventing fatigue
  failures of hanger caused by vibrations

• Hoga Kusten Bridge, Sweden - dehumidification
  system for the main cables
• Aquitaine Bridge, France - deck widening and
  replacement of main cables
• Messina Bridge, Italy - design for 200 years
  service life

5
New Little Belt Bridge, Denmark

• Introduction
• Location connect East and West Denmark
• Opened to traffic in 1970
• Main span - 600m
• Total length of suspension part 1080m
• Total length - 1700m
• Bridge deck steel box girder
• Optimal corrosion protection

6
New Little Belt Bridge, Denmark

• Dehumidification of the main girder - backgrounds
• Steel bridge structures must be protected from
  corrosion

• Traditionally by surface treatment - blasting and
  painting
• Service life of coating - 25 years very short
  compare to 120-200 years of expected service life
• Workers health hazards
• Dehumidification proven superior in all aspects
  technically, economically and environmentally
• Basic concept RH below 60

7
New Little Belt Bridge, Denmark

• Dehumidification
• First application box girder ofthe Little Belt
  Suspension Bridge
• In service since 1970, only maintenance no
  replacement
• Documented by monitoring system and physical
  proof no corrosion on steel plate samples
• Presently, virtually worldwide standard applied
  to many major bridges
• Other bridge applications - anchor houses and
  boxes, cable saddles, abutment rooms, main cables

8
The Great Belt Link

• Location -Connects Zealand with Funen in Denmark
• Opened to traffic 1998

9
Great Belt Bridge, Denmark

• Introduction
• Main span - 1624m
• Total length of suspension part 2694m
• Total length - 6790m
• Bridge deck steel box girder
• Main challenges reduce the number of movement
  joints and bearings to minimum, mitigate
  vibrations of the longest hangers to enhance
  their fatigue life

10
Great Belt Bridge, Denmark

• Enhancing service live of bearings, expansion
  joints and other moving devices
• Bridges should be arranged with as few moving
  elements as possible
• All moving elements have to be inspected and
  maintained regularly - more often than other
  bridge elements
• They have to be very durable
• They have to be easy to maintain and replace

11
Great Belt Bridge, Denmark
12
Great Belt Bridge, Denmark

• Enhancing service live of bearings, expansion
  joints and other movement devices
• Long continuous sections reduces the number of
  expansion joints and bearings
• Introduction of the hydraulic buffers at the
  anchor block restrains movements due to live
  loads and reduces wear of expansion joints and
  bearings

13
Great Belt Bridge, Denmark

• Vibration of cable stays and hangers
• Vibrations of stay cables under the combination
  of rain, wind and frost are observed at many
  major cable supported bridges
• It is important to minimize these vibrations to
  such extent that the structural integrity is
  maintained and fatigue failure will not occur
• Several vibration mitigation alternatives can be
  used
• Cable separators
• Spiral ropes
• Wind ropes
• Liquid dampers
• Hydraulic dampers

14
Great Belt Bridge, Denmark

• Data for hangers
• Cable Diameters incl. PE - Sheating- 79 mm (64
  ) - 89 mm (28 )- 112 mm (8 )
• Maximum Length 177 meters
• Natural Frequency 1st mode 0,44 Hz to 1,00 Hz
  (length above 100 m)
• Hanger Damping ratio 0,20 rel. to critical

Locked coil cables
Separator
15
Great Belt Bridge, Denmark

• Visual observations
• Road Patrol and others
• Camera operated from O-Room
• Monitoring system
• Accelerometers
• GPS (Global Positioning System)
• Tiltmeters

Camera
Bi-axial accelerometer on a hanger
16
Great Belt Bridge, Denmark

• Inspections

• Observed damages to spacers in the longest cables
• Observed damages to lock plates of the top
  sockets also in the longest cables

17
Great Belt Bridge, Denmark

• Mitigation of vibrations
• Separators (part of the design)
• Spiral Ropes (installed 2001)
• Wind Ropes (installed 2001-2002)
• Tuned Liquid Dampers (installed 2004)
• Hydraulic Dampers (installed 2005)

Hydraulic Dampers
Wind Ropes
Tuned Liquid Dampers
Spiral Ropes
18
Great Belt Bridge, Denmark

• Mitigation of vibrations
• Spiral ropes
• Installed on 2-nd and 3-rd hanger from the West
  Pylon on the South side

Spiral Ropes
19
Great Belt Bridge, Denmark

• Mitigation of vibrations
• Wind Ropes
• East to West Pylon on the North side
• - Level 69 m a.d.
• - Level 114 m a.d.

20
Great Belt Bridge, Denmark

• Mitigation of vibrations
• Tuned Liquid Dampers
• Installed on 1st, 2nd and 3rd Hanger from the
  East to East Pylon on the North side

Tuned Liquid Dampers
21
Great Belt Bridge, Denmark

• Mitigation of vibrations
• Hydraulic Dampers
• 2nd Hangers from West Pylon, South side

22
Great Belt Bridge, Denmark

• Accessibility

23
Hoga Kusten Bridge, Sweden

• Introduction
• Location - E4 over Angerman River (400km north of
  Stockholm)
• Opened to traffic in 1998
• Main span - 1210m
• Total length - 1800m
• Main cables diameter - 650mm
• Main challenge preventing corrosion of main
  cables by dehumidification

24
Hoga Kusten Bridge, Sweden

• Deterioration of main cables and hangers
• Serious problem in cable supported bridges
  worldwide
• Corrosion - most common deterioration mechanism
  of main cables and hangers
• The basic cause of corrosion is the presence of
  water or moisture
• Salt spray from the sea
• De-icing salt
• Pollutants from vehicles or industry

Luangawa Bridge
Zárate Bridge
25
Hoga Kusten Bridge, Sweden

• Deterioration of main cables and hangers
• Traditional corrosion protection systems can slow
  down the corrosion but can not prevent it

• Dehumidification system
• Complete corrosion protection due to elimination
  of the source of corrosion problem
  water/moisture
• Main cables are enclosed in an atmosphere with
  low relative humidity that prevent corrosion
• Several years of experience shows that this is
  the most efficient solution from the Life Cycle
  Cost point of view

26
Hoga Kusten Bridge, Sweden

• Three major components of dehumidification system
• Sealing system including cable bands, saddles and
  other components
• Dehumidification system capable of producing and
  blowing dry air through the main cables
• Control monitoring system

Dry air is blown along the cable to keep it dry
Steel wrapping wire
Elastomeric band is wrapped around the cable and
bonded by heating
27
Hoga Kusten Bridge, Sweden
Principles for wrapping
Main cable voids gt 21
28
Hoga Kusten Bridge, Sweden

• Dehumidification layout
• Buffer tanks in bridge girder and pylon cross
  beams
• Monitoring of RH, temperature, pressure and air
  flow

29
Hoga Kusten Bridge, Sweden

• Installation of the dehumidification system

30
Aquitaine Bridge, France

• Introduction
• Location Bordeaux,
• over Garonne river
• Opened to traffic in 1967
• Main span - 400m
• Total length - 700m
• Main problems
• Advanced corrosion of the main cables
• New broken wires were detected every week
• Insufficient traffic flow capacity new traffic
  lanes needed

31
Aquitaine Bridge, France

• Scope of work
• Secure the bridge immediately against collapse
  (Broken wires were detected weekly)
• Secure the bridge for repair works
• Design of a new cable system
• Main cables
• Cable bands
• Suspenders
• Deck enlarged from 4 lanes to 6 lanes
• No interruption of the app. 80 000 vehicles a day

Additional temporary cables
Details of corroded strands
32
Aquitaine Bridge, France

• Enlargement of tower top

33
Aquitaine Bridge, France

• New anchorage of main cable outside and behind
  the old one

34
Aquitaine Bridge, France

• Replacement of Main Cable
• Replacement of hangers

35
Aquitaine Bridge, France

• New permanent hanger anchorages

• New cable clamp

36
Challenges in the futureThe Messina Bridge
37
Challenges in the futureThe Messina Bridge

• Challenges
• The worlds largest suspended span of 3300 m
• Road as well as rail traffic
• Triple box concept for the deck
• Seismic
• Wind
• Design life 200 years

38
Challenges in the futureThe Messina Bridge

• Triple Box Concept for the Suspended Deck
• Main elements cross girders spacing 30 m
• Secondary elements two longitudinal roadway
  girders and one central railway girder spanning
  between the cross girders

39
Conclusions

• Modern suspension bridges are expected to be in
  service for up to 200 years
• Service Life Approach has to be used in their
  design
• Proactive design and preventive maintenance
  strategy should be used as a principal solutions
  for dealing with various possible deterioration
  and serviceability problems
• Suspension bridges have to be constructed from
  very durable, high performance materials
• All the elements of suspension bridges with
  service life lower than the service life of the
  bridge have to be easily accessible for
  inspections and easy to maintain and replace
• Modern suspension bridges have to be designed
  allowing for replacement of certain elements with
  no, or with only minor, disturbance to the traffic

40
Challenges in the futureThe Fehmarn Belt Bridge