2383

These strands were placed and tensioned one-

by-one. Individual placement was extremely economical, but tensioning required a new

technique, already developed by the cable

supplier for the erection of three bridges: the

Arrade and Guadiana Bridges in Portugal,

and the Chalon-sur-Saone Bridge in France.

The fast strand of each cable is tensioned to a

computed value and equipped with a pressure cell which gives the tension at any time. Each

new strand, when installed, is tensioned to

have exactly the same tension as the pilot strand at that precise moment, which is given by the cell. All strands thus receive the same

tension, which is the desired one if the initial

tension of the pilot strand had been appropriately computed. If not. an adjustment

is made the same way. This process is not

susceptible to influences from temporary operations, such as the movement of construction equipment.

Finally, cables received an external duct made of a series of two half-ele- ments which are forced into each other. These ducts are not for corrosion protection; they are air and water permeable. They aim at reducing drag

forces and avoiding rain-induced vibrations of the cables. In addition, they totally eliminate the vibrations of strands in the bunch which makes each cable, which are produced by wind interaction between strands by a kind of "wake" effect.

Interconnecting Ropes

In his design for the Messina Straits, Fritz Leonhardt envisioned connecting all cables in each plane of the cables by tying ropes, which aimed at increasing the apparent modulus of elasticity of the suspension, lowered by sag effects in long cable-stayed spans. In some other bridges, such as the Faro Bridge in Denmark or the two cablestayed bridges of the Kojima-Sakaide route of the Honshu-Shikoku link, ropes were, installed to limit cable vibration which was rain-induced in the Faro Bridge and coming from the wake effect in the Japanese bridges.

The purpose is totally different in the Normandie Bridge: due to the very, long span of the bridge, the main vibration period for vertical bending would have been of the same magnitude as the vibration period of the longer cables, 4.5 s, compared to about 4.0 s. In this situation, it was feared that cable vibrations would be induces by the deck movements. Interconnecting ropes were designed to totally change the vibration periods of cables, at least transversally, reducing them to 1.25 s and less.

Four ropes connect all cables in each plane of stays. Their tension was selected to avoid de-tensioning from vi-

brations produced by wind turbulence.			sketches and of premature options and
Their constitution is composite, with			decisions.
steel and plastic to increase fatigue re-			Although there was no public money
sistance because it is obviously diffi-			in the Normandie Bridge, the French
cult to simultaneously achieve a high			government had to approve the project.
damping coefficient and a high fatigue			The Road Director at the time, lean
resistance.			Berthier, decided to invite an as-
Concluding Remarks			essment of the design by an
			international group of experts: Marcel
			Huet (Project Manager of the
The design and construction of very			Tancarville Bridge), Henri Mathieu,
large bridges which go beyond existing			Charles Bngnon, Roger Lacroix, Rene
limits require the strongest determina-			W'alther and Jorg Schlaich. This group
tion from the Owner, who must invest			proposed various amendments, some
enormous confidence in, and support			of which were included in the final de-
of, the engineers in charge. The most			sign.
dangerous	tempests	that audacious	Nevertheless, some engineers from one
projects face are not produced by wind			of the erection contractors considered
on site, but by antagonistic opinions			the wind forces to have been un-
that find a willing audience.			derestimated and, thus, the safety
The success of the Normandie Bridge			questionable. The debate became pub-
is due in large part to the confidence			lic, even international.
and support that the project received			The Owner and the Road
from the Owner, the Road Director and			Director decided to consult Alan
the local authorities. Some organi-			Davenport to evaluate the wind tunnel
sational aspects and some episodes			tests and the estimated wind forces. He
during construction indicate the deci-			approved the performed analyses and
sive importance of human factors.			recommended some additional wind
The Owner gave the design engineers			tunnel, tests, the results of which were
total responsibility for the design and			even more favourable than the first
granted them complete freedom to as-			evaluations. This confirmation of the
semble the design team. Under these			design helped the project very much,
circumstances, improvements could be			and from the summer of 1991, all
introduced at each step of the project,			contractors worked with enthusiasm
with no consideration other than effi-			and energy to complete the bridge on
ciency. This is far superior to design			schedule, within budget and up to the
competitions, now preferred by some			prescribed standards of quality.
administrations, where projects can be			Any decision can be questioned, any
selected based not always on structural			action criticised. The clear conclusion
; aspects, and where designers can			is that a complex and ambitious project
become	prisoners	of their initial	like the Normandie Bridge cannot be
			successfully realised without a strong

Project Manager - as Bertrand

Structures

and Buildings,

August,

Deroubaix has been for this project -to

1993, pp. 281-302.

B. Presentation

guide it over the years from conception

[6] DEROUBAIX,

to completion, even when questioned

du projet et developpement de la

from many sides. Going further than

constructio . In: Le point sur le Projet

ever before in any given field calls for

du Pont de Nor mandie. Annales de

courage. The Owner and the local

1'ITBTP, Paris, September-October

authorities remained

totally

confident

1993.

in the design and in the engineers in

[7] LEGER, P. Finaiicvment du Pont

charge, even in difficult times. This

de Normandie. ibid.

was decisive for success; complex

[8] DAVENPORT, A. Analyse des

structures cannot be built with

etudes des effets du vent sur le Pont de

hesitations and doubts!

Normandie. ibid.

References

[9] VIRLOGEUX, M. Le projet du

[1]

VIRLOGEUX. M.;

FOUCRIAT,

Pont de Normandie. ibid.

J.-C; DEROUBAIX, B. Design -of the

Owner:

Normandie Cable-Stayed Bridge near

Chambre de Commerce et d'lndustrie

Honfleur. Proc. of the Int. Conf. on

du Havre

Cable-Stayed Bridges, Bangkok, pp.

Project Management:

1111-1122, November, 1987.

[2] V1RLOGEUX, M. Projet du Pont

Mission du Pont de Normandie

de Normandie, Conception generate de

I'ou-vrage. Proc. of the 13th IABSE

Design:

Congress,

Helsinki,

IABSE,

June,

SETRA,

Sofresid,

Quadric,

SEEE,

1988.

Sogelerg, Setec and Europe-Etudes

[3] DEROUBAIX, B.; VIRLOGEUX,

Gecti. Architect: Charles Lavigne

M.

Design and Construction of the

Wind Laboratories:

Normandie Bridge. Proc. of the IABSE

CSTB and ONERA

Symposium,

St

Petersburg,

Russia,

Contractors (concrete): GIE du Pont

September 1991.

[4] VIRLOGEUX, M. Wind Design

du Normandie (Bouygues, Campenon

and Analysis for the Normandie

Bernard,

Dumez,

GTM, Quillery,

Bridge. In: 'Aerodynamics of Large

Sogea. Spie Batignolles

Bridges,'

A.

Larsen,

ed.

Balkema,

Contractors (steel):

Rotterdam 1992, pp. 183-216.

[5]

VIRLOGEUX,

M. Normandie

Monberg and Thorsen

Bridge:

Design

and

Construction.

Sub-contractors:

Proc. of

the

Inst.

of

Civil

Engs,

Bilfinger -\ Berger, Freyssinet, Munch,

Lozai,VSL, SDFM	Service date:
	January 1995

THE RAINBOW BRIDGE, JAPAN

Kazuo Yamazaki, Mgr, Design and Design Div. Mitsunobu Ogihara, Research Div. Kimihiko Izumi, Mgr, Chief, Design Div. Metropolitan Expressway Public Corp., Tokyo,

Japan

Introduction	The bridge is a 3-span, 2-hinge stiffen-
The Rainbow Bridge has become a	ing truss suspension type with a centre
new landmark in the Port of Tokyo.	span of 570 m and a total length of 798
The bridge provides direct access	m (Fig. 30). It has a double deck
between central Tokyo and a wa-	construction: the upper deck carries
terfront development now under con-	two two-lane expressways while the
struction. It also connects two express-	lower carries two two-lane roads serv-
ways on both sides of the Port, creating	ing the Port, as well as a railway and
the first express route across the city	footpaths (Fig. 31). The diameter of
and is expected to significantly ease	the main cable is 762 mm.
traffic congestion in the centre of
Tokyo.

Fig. 30

The bridge is founded on mudstone	for the Port of Tokyo crossing to satis-
(consolidated silt or soft rock) far be-	fy three significant constraints:
low the surface. Few suspension	- 500 m wide ship access with 50 m
bridgeshave their foundations on	clearance
mudstone and several innovative tech-	- main tower height, including erec-
nologies were employed to overcome	tion equipment, of less than 155 m due
this unfavourable condition.	to the proximity (9 km) of Haneda
Planning	International Airport.
	- limited length for the side spans to
	link up with existing expressways on
A suspension-type bridge was selected	both sides of the bridge.

A cable-stayed bridge could have been considered for the 570 m span, however the height of the towers for this type of design would have been about 200 m. Besides, a cable-stayed design would have suffered excessive negative reaction (uplift) at the link shoe of the side spans. For these reasons and economic considerations, a suspen- sion-type bridge was determined to be the best choice.

Fig. 31

Substructure

The water depth at the site is approximately 12 m, and the subsurface ground consists of a weak alluvial clay layer on top of a mudstone stratum. The mudstone bearing layer was found at levels between -30 and -38 m.

Pneumatic caisson foundations were designed and constructed for the two

main towers and the two anchorages. The anchorage caissons are 70 m X 45 m. One anchorage caisson v as constructed at sea using a steel box caisson prefabricated in a shipyard; the other was constructed on land.

For the pneumatic caissons, robotic excavation was employed. A computercontrolled caisson shovel was operated remotely using a video camera. Excavated materials were placed onto an automatic belt conveyer for removal. This method ensured worker safety and construction efficiency under the high atmospheric pressure (3.5 bar) in the caisson's chamber. In addition, special digging machines were used for the excavation of the hard mudstone.

Since an anchorage would be subjected to a huge eccentric force due to the cable tension (230 MN) a precise prediction of long-term (100 years') deformation of the mudstone bearing layer was essential) The initial prediction was modified repeatedly using a measured displacement at each construction stage, and the values obtained were considered in the design of the superstructure.

Item	Content
Type of bridge	3-span, 2 hinged-stiffening truss, doubledeck suspension
girder
Span layout	Stiffening truss: 107.5 + 562.0 + 107.5 m
	Cable: 147.5 + 570.0 + 147.0 m
Tower works
Structural type:	Longitudinal direction: flexible hinge at top of tower
	Transverse: 3-story frame rigid (1 story above road)

Tower height:	121.866 m (cable theoretical top: 126.0 m)
Height of tower	P36	(Shibaura Main Tower): 2.866 m
foundation:	P37	(Daiba Main Tower): 4.5 m
Centre distance	P36	(Shibaura Main Tower) at foundation:	30.862 m
between towers:		at tower top:	30.084 m
	P37	(Daiba Main Tower) at foundation:	30.851 m
		at tower top:	30.084 m

Cable works
Cable type:	PWS (parallel wire strand)
Structure	Main span sag: /= 57.6 m; sag ratio: n = 1/9.9
dimensions:	Centre distance between cables: 29.0 m
Cable diameters:	Main span: 762 mm; 127 strands per cable
	Side span: 771 mm; 130 strands per cable
Strand:	Diagonal; 69.8 mm 0
Wire:	5.37 mm 0; tensile strength: 160-180 kg/mm2
Hanger rope:	Centre Fit Rope Core (CFRC); 4 ropes/panel point
Stiffening girder works
Structural type:	Main structure: parallel chord Warren truss
	Lateral bracing: K-truss
Hanging type:	Anchoring to upper chord
Structure	Main structure height: 8.9 m
dimensions:	Main structure width: width: 29.0 m
Upper floor	Expressway (multi-span continuous steel deck
system:	girder, effective width: 9.25 m) Note: Main span is
	of 56 span continuous structure, rigidly connected at
	both ends
Lower floor	Port roadway (multi-span continuous steel deck
system:	girder, effective width: 7.5 m, including walkway
	1.5-2.5 m wide)
	Rail transportation system (multi-span continuous
	steel deck girder, RC track gauge: 1.7 m)

Table 3: Basic structural specifications

The concrete volume of each anchor-	ing in temperatures of about 3°C for
age, including the top slab of the cais-	the sand and -27 to 15 °C for the grav-
son, amounted to 60000 m3. In order to	el. Finally, preset water pipes further
reduce cracking caused by the heat of	helped to cool the mix after placement.
hydration, an ultra-low-heat cement	Superstructure
was used. In addition, liquid nitrogen
was sprayed onto the aggregate, result-

The steel weights for the superstructure included 14100 t for the towers; 83001 for the cables, 23 7001 for the stiffening girders. The basic specifications for the tower, cable and stiffening girder works are shown in Table 3.

main cables, free-standing towers of suspension bridges experience vibration due to wind forces. Based on wind tunnel tests, damping devices including an active mass damper, were installed at the tower tops to resist possible vortex-excited vibration.

A main cable consists of 130 strands (each composed of 127 wires) in the side spans and 127 strands in the centre span. Since the short side spans of the Rainbow Bridge might have encountered a problem due to unbalanced tensile forces in the main cables on each side of two towers, three additional cable strands were installed in the side spans to balance the stress level in the main cable. In addition, a "horizontal frictional board" with an increased surface friction coefficient was fitted to the towers' top cable saddles to further resist cable slippage due to any unbalanced tension. After erection of the strands, the cable was shaped using a squeezing machine.

The Rainbow Bridge also features a multi-continuous (56-span continuous) steel deck floor system with improved shoes on its upper deck. There are no expansion joints in the centre span of the expressway, resulting in a comfortable driving surface and reduced maintenance requirements.

AESTHETICS

Fig. 32

The main towers (Fig. 32) are made of hollow steel box section and were each assembled in three large blocks using 33001 and 41001 (hanging weight) floating cranes. Until erection of the

From the outset, the owner was very conscious of the environmental and visual impact of the bridge, given its prominent location in the Port of Tokyo. A Committee on Aesthetics was established and much attention

was paid to architectural and structural				illumination	design,	the	Rainbow
details throughout the design and				Bridge was awarded the Paul
planning of the crossing.				Waterbury Award of Distinction for
The rounded corners and reduced bolt				Outdoor Lighting by the Illumination
connections of the main towers'				Engineering Society of North America.
columns and beams, as well as the con-				Owner/Engineers:
figuration and surface finish of the an-						Metropolitan
chorages, resulted from aesthetic con-				Expressway	Public	Corp.	(MEPC),
siderations. The graceful configuration				Tokyo
of the bridge is illuminated at night by				Construction duration: 6.5 years
white, green and coral pink lighting.
The lighting pattern varies with the				Service Date: August, 1993
seasons and times of day. For its
THE TÄHTINIEMI BRIDGE, FINLAND
				land, with a total length of 924 m. The
Esko Jarvenpaa, Technical Dir.				main span is 165 m and the width of
Pekka	Pulkkinen,	Civil	Eng.	the deck varies from 22 to 30 m.
Suunnittelukortes AEK		Ltd,	Oulu,
Finland
Reiner Saul, Managing Dir.
Leonhardt, Andra and			Partner,
Stuttgart, Germany					Fig. 33

INTRODUCTION	DESIGN COMPETITION
In 1988 the Finnish Roads Administra-	The competition was limited to four
tion organised a design competition for	Finnish bridge engineering companies.
a technically advanced bridge which	The design brief was very demanding.
would adapt well to the lake landscape	Among the most important parameters
near the city of Heinola. Heinola is one	were the site, the difficult foundation
of the most beautiful cities in Finland,	conditions, the curvature of the
about 130 km north of Helsinki on the	roadway and the need to maintain free-
route to a lake area where many	flowing marine traffic, including a
vacation cottages are located.	busy logging channel. Maximum water
The winner of the competition, now	depth at the site is 24 m, and the bridge
known as the "Star of Heinola", is a	is situated in a natural lake landscape,
single-pylon cable-stayed bridge (Figs.	near the town.
33, 34). It is the largest bridge in Fin-

Ten proposals were delivered to the	was required, there were inclined steel
competition jury. Five were traditional	struts in the cross sections of two steel
composite girder designs; one was a	girder designs for this type.
single pylon design and three were	The cross section alternatives for the
double-pylon cable-stayed designs.	cable-stayed bridge designs were a
There was also one truss bridge pro-	concrete box girder, a composite gird-
posal.	er, a composite box girder and a com-
In the superstructures of the composite	posite slab beam which was pre-
girder bridges, reinforced compression	stressed in two directions.
slabs were used in the areas of the	The foundation solutions were very
intermediate supports, and longitudinal	similar in all bridges. In deep water,
prestressing in the deck slab. Due to	composite steel pipe piles were used.
the considerable width of the deck that

Fig. 34

Other supports were founded on soil or	signed for far heavier traffic loads than
rock. The diameter of the piles varied	current Finnish load codes specify.
from 700 to 1500 mm.	Deviating from Finnish load specifica-
The winning design, with its single	tions, the full traffic load can be car-
105 m high pylon, serves as a dramatic	ried on one side of the bridge deck
gateway to the lake district of Finland.	when there is simultaneously a special
Its cable-stayed spans are placed over	heavy truck on the other. If the cables
the open lake so that the heavy marine	have to be changed in the future, only
traffic can operate with minimal ob-	one edge lane has to be closed. Also,
struction.	the pylon was designed for greater
	wind loads than specified in the
BRIDGE DESIGN	existing code. Crash loads of ships
	have been taken into consideration in
The client wanted to assure adequate	the design of the intermediate support.
traffic-handling capacity of the bridge	The five middle supports are founded
far into the future as well as under ex-	on composite steel pipe piles; other
ceptional circumstances. Thus, it was	supports are founded on soil or rock.
decided that the bridge should be de-	The steel piles were designed as a