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2. CONTENTS
10.6 MULTI-SPAN CABLE-STAYED BRIDGES
10.7 CABLE-STAYED BRIDGES FOR RAILWAYS
10.8 AERODYNAMICS ASPECTS
10.8.1 CABLE VIBRATIONS
10.8.2 GIRDER
10.8.3 PYLON
10.8.4 WIND TUNNEL TESTING
10.9 ARCHITECTURAL LIGHTING

3. MULTI-SPAN CABLE-STAYED BRIDGES

4. In the absence of anchor stays live load in the main span would result in significant bending in the pylon.
In a multi-span arrangement there are no anchor stays to provide restraint of the central pylons and overall
stability has to be provided by other means.
The following measures to stabilize a multi-span cable-stayed bridge have all been adopted in
practice:
(a) Arrange pylons with substantial stiffness in the longitudinal direction of the bridge.
(b) Introduce additional tie-down piers to provide efficient anchorage to stabilize the central pylons.
(c) Stabilize the central pylons by introducing tie cables from the top of the central pylons to the
girder-pylon intersection point at the adjacent pylons.
(d) Stabilize the pylons by adding a horizontal stay connecting the pylon tops.
(e) Arrange crossover stay cables in the main spans.
10.6 MULTI-SPAN CABLE-STAYED BRIDGES

5. 10.6 MULTI-SPAN CABLE-STAYED BRIDGES

6. 10.6 MULTI-SPAN CABLE-STAYED BRIDGES
EXAMPLES OF MULTI-SPAN CABLE-STAYED BRIDGES
MARACAIBO BRIDGE
RION-ANTIRION BRIDGE
In the Maracaibo Bridge, overall stability is provided b
y the extremely rigid pylons designed with an inverted
V-shape in the longitudinal direction. An additional
V-shaped bracket supports the deck and provides a
moment stiff connection for the cantilevers on either
side of the pylons. Simply supported spans
(drop-in spans) connect the cantilevers at the center
of the main spans.
The pylons of the Rion-Antirion Bridge in Greece,
completed in 2004, have an inverted V-shape in
both directions and a significant bending stiffness
but in this case the stiffening girder is continuous.
The three main spans are 560 m (1837 ft) long each
.

7. 10.6 MULTI-SPAN CABLE-STAYED BRIDGES
EXAMPLES OF MULTI-SPAN CABLE-STAYED BRIDGES
The spectacular Millau Viaduct completed in 2004 consists of six main spans of 342 m (1122 ft) and
two side spans of 204 m (669 ft). The superstructure with a total length of 2460 m (8071 ft)
is continuous from abutment to abutment. The inverted V-shape pylons are 90 m (295 ft) tall and supported
on the superstructure that in turn is fixed to the piers. The piers, where the tallest is 245 m (805 ft)
above ground, are of a very sophisticated design allowing a favorable distribution of stiffness between
superstructure, piers and pylons.
MILLAU VIADUCT

8. 10.6 MULTI-SPAN CABLE-STAYED BRIDGES
EXAMPLES OF MULTI-SPAN CABLE-STAYED BRIDGES
SECOND ORINOCO BRIDGE
TING KAU BRIDGE
The Second Orinoco Bridge in Venezuela has two 300 m
(984 ft) long cable-stayed navigation spans separated by
a central cable-stayed section containing a common
anchor pier corresponding to the concept (b).
A design based on tie-cables from the central pylon
to the girder-pylon intersection point at the
adjacent pylons, concept (c), is found in the Ting
Kau Bridge in Hong Kong S.A.R., China (completed
in 1998).

9. 10.6 MULTI-SPAN CABLE-STAYED BRIDGES
EXAMPLES OF MULTI-SPAN CABLE-STAYED BRIDGES
SECOND MACAU-TAIPA CROSSING
MUNKSJON BRIDGE
The Second Macau-Taipa Crossing can be considered as
a crossover between system (b) and (c) in the list above
as the tie-cables connect the two central pylons only.
The Munksjön Bridge in Sweden with
a total length of 260 m (853 ft)
consists of four main spans of 44 m
and the central pylons are stabilized
by a top stay.

10. 10.6 MULTI-SPAN CABLE-STAYED BRIDGES
EXAMPLES OF MULTI-SPAN CABLE-STAYED BRIDGES
The New Forth Crossing across the Firth of Forth in Scotland consists of two main spans and three
pylons. Stability of the central pylon is provided by crossover stay cables in the main spans that ensure that
the flanking pylons and their anchor stays are activated for unbalanced live loads.
THE NEW FORTH CROSSING

11. CABLE-STAYED BRIDGES FOR RAILWAYS

12. Most cable-stayed bridges carry only road traffic and/or pedestrian traffic. However, cable-stayed bridges
have also been designed to carry light rail or heavy railway load, often in combination with road traffic.
The requirements to maximum slope, deflections and rotations are stricter for a bridge carrying
railway than for roadway traffic only. In particular the differential angular rotations under live load at
movement joints between adjacent girders need special attention. Furthermore, the loads in the
longitudinal direction of the bridge due to trains braking and accelerating are significant.
The dynamic amplification of the loads shall be taken into account in the structural design and the
accelerations shall be evaluated in terms of comfort and safety of the train passengers. A runability
analysis is carried out to verify the dynamic train-track-structure interaction due to moving loads on
the flexible structure.
10.7 CABLE-STAYED BRIDGES FOR RAILWAYS

13. 10.7 CABLE-STAYED BRIDGES FOR RAILWAYS
EXAMPLES OF CABLE-STAYED BRIDGES FOR RAILWAYS
One of the earliest examples is the twin bridges across the Paraná River in Argentina (Zárate-Brazo Largo
Bridge I and II), which opened for railway traffic in 1978. These two identical cable-stayed bridges with main
spans of 330 m (1083 ft) carry four lanes of roadway traffic and a single railway track over the two main
branches of the Paraná River. The railway track is located eccentrically next to the traffic lanes on the one
level girder. One of the stay cables suddenly failed in 1996 and subsequently all stay cables were replaced.
THE PARANA RIVER (ZARATE-
BRAZO LARGO BRIDGE I&II)

14. 10.7 CABLE-STAYED BRIDGES FOR RAILWAYS
EXAMPLES OF CABLE-STAYED BRIDGES FOR RAILWAYS
The Skytrain Bridge in Vancouver, Canada, opened in 1990 and carries two tracks of light rail across
the Fraser River. The superstructure is a one-level prestressed concrete girder. The main span is 340 m
(1115 ft) and the bridge carries no road or pedestrian traffic.
SKYTRAIN BRIDGE

15. 10.7 CABLE-STAYED BRIDGES FOR RAILWAYS
EXAMPLES OF CABLE-STAYED BRIDGES FOR RAILWAYS
The cable-stayed bridge of the Øresund Fixed Link between Denmark and Sweden opened for traffic in
2000 and has a main span of 490 m (1608 ft). The stiffening girder is a two-level truss structure with the
double track railway located on the lower deck. The trusses and the lower deck are in steel whereas the
upper deck is in concrete. The depth of the girder is 11 m (36 ft), which provides significant stiffness and
distribution of local, concentrated loads. The pylons are H-shaped with the cross girder located underneath
the girder. The stay cable spacing is 20 m (66 ft) at deck level and the stays are arranged in a harp system.
ØRESUND FIXED LINK
BETWEEN DENMARK
AND SWEDEN

16. AERODYNAMIC ASPECTS

17. 10.8 AERODYNAMIC ASPECT
10.8.1 CABLE VIBRATIONS
A number of different vibration phenomena have been reported on completed cable-stayed bridges and
during construction, including;
(a) Rain-wind induced vibrations - the most common cause of stay cable vibrations. This is related to the
formation of water rivulets on the upper and lower surface of the stay cable under the combined action of
rain and wind. This changes the characteristics of the cable that in turn causes a change in the forces acting
on the cable.
(b) Vortex shedding induced vibrations and galloping - occurs in the crosswind direction. Vortices form
behind the stay cable in smooth airflow and when the frequency of vortex shedding is close to a natural
frequency of the stay cable vortex resonance or lock-in occurs. Vortex shedding induced vibrations occur at
limited wind speed ranges matching the natural frequencies of the stay cable. Galloping may be observed
when ice-coating changes the cross section of the stay cable.
(c) Indirect excitation - Vibration of the cable anchorage points may cause the stay cables to vibrate. This is
referred to as indirect excitation. Both vibrations of the anchorage points in the direction of the cable and
perpendicular to the cable can result in stay cable oscillations of high amplitude.

18. 10.8 AERODYNAMIC ASPECT
10.8.1 CABLE VIBRATIONS
Mitigation measures to counteract stay-cable vibrations can be classified into three groups:
(1) Aerodynamic control - involves changes of the shape of the element that is susceptible to vibrations.
Modification of the cable surface by introducing dimples or helical fillets to mitigate rain-wind induced
vibrations belong to this group.
(2) Structural control - modifies the mass or stiffness of the element and an example is the provision of
cross ties that changes the natural frequency of the stay cables.
(3) Mechanical control - is achieved by the application of damping devices. These devices are attached
directly to the stay cables and thereby dampen cable oscillations. In the case of indirect excitation damping
devices can be located at the stiffening girder and/or pylons to reduce the vibrations of the cable support
points.

19. 10.8 AERODYNAMIC ASPECT
10.8.2 GIRDERS
Buffeting is the dynamic response of the bridge to gusty wind. Box girders adopted for long spa
n cable-stayed bridges are often aerodynamically shaped to reduce the wind load effects. An
aerodynamically shaped “nose” can be either structural or non-structural in which case it is
often referred to as a wind fairing. However, vortices can form if the flow detaches from the
surface at the downwind corners. Vortex shedding excitation of the stiffening girder occurs
when the vortex shedding frequency matches the natural frequency of one of the vertical
girder modes. Typically the lower order modes are more critical and vortex shedding excitation
will occur at relatively low wind speeds where the flow is smooth. Guide vanes, wind fairings
and splitter plates have been adopted in practice and have proven efficient in preventing the
formation of vortices.

20. 10.8 AERODYNAMIC ASPECT
10.8.3 PYLON
Depending on the cross sectional shape pylons may be susceptible to vortex shedding
that may in turn cause the stay cables to oscillate due to indirect excitation. This can
be counteracted by modifying the cross section to a more favorable shape, for instanc
e by introducing corner cuts, by installation of deflector plates or tuned mass dampers
.

21. 10.8 AERODYNAMIC ASPECT
10.8.4 WIND TUNNEL TESTING
Computational fluid dynamics (CFD) is a useful tool, which can be used to study and
optimize the cross sectional shape of girders and pylons. Section model wind tunnel
testing provides the wind load coefficients and can also provide input for the
assessment of vortex shedding excitation and flutter stability. Full aeroelastic bridge
model tests are used to check the buffeting response and flutter stability of the bridge
during construction and in the completed stage. Terrain models can be used to
provide specific information on the wind climate including the turbulence intensities
at the bridge site if site measurements are not available or need to be supplemented.

22. ARCHITECTURAL LIGHTING

23. Lighting schemes can be static or the lighting controls can be dynamic, and should be
programmed such as not to distract traffic. The light intensity shall be adjusted to
match the surroundings of the bridge.Environmental and sustainability aspects are
obviously an important part of the design of architectural lighting that should consider
issues such as energy consumption and how light pollution can be avoided. The recent
development in LED lighting technology and lighting controls has added to the
popularity of architectural lighting.
10.9 ARCHITECTURAL LIGHTING