2383

Brett H. Pielstick, Civil Eng.

of the old crossing which lay between

Steinman,

Boynton,

Gronquist &

a railroad bridge and the new bridge.

Birdsall, Daytona Beach, FL

The third and final stage of construc-

Project Description

tion entailed maintaining traffic on the

new eastern bridge and constructing

The new Acosta Bridge is a USD 148

the western bridge.

Scour Protection

million project crossing the St. John's

River in

downtown

Jacksonville,

Florida. This project features twin five-

As downtown Jacksonville grew, more

span structures, each totalling 501 m in

land was created by filling the St.

length.

Cast-in-place

segmental

John's River in areas adjacent to the

concrete box girder construction was

Acosta Bridge. The substantial reduc-

used throughout with the exception of

tion in river area created a scour con-

the approach spans.

dition that removed over 10 m of ma-

The asymmetrical main span of 192 m

terial from areas around the founda-

was built by balanced cantilever con-

tions of the old bridge. Several founda-

struction with traveling forms. The ap-

tions of the old bridge had only 0.6 m

proach spans for the river crossing

of embedment remaining at the time of

were constructed span-by-span on

demolition. After the superstructure of

falsework. The approaches and corre-

the old structure was removed, stability

sponding ramps to the river bridge

cables were required to keep the old

were constructed of steel plate and box

columns from falling over.

girders.

Gabion mats were used to combat the

The project was designed to be con-

extreme scour conditions around the

structed in three separate stages in or-

old Acosta Bridge, the 60 year old rail-

der to maintain the flow of traffic and

road bridge, and the new Acosta

limit the amount of additional right of

Bridge. These 4.9 m x 11.0 m mats

way required for the new structure.

were constructed using PVC-coated,

Stage one involved the construction of

chain link fabric mesh mattresses filled

the eastern three lane bridge, while

with rock to a thickness of 230 mm.

traffic was maintained on the old

The gabion mats were placed in layers

Acosta Bridge. Stage two involved the

on the river bottom arid laced together

placement of traffic on the new eastern

underwater. Rip-rap and filter fabric

three lane bridge, allowing demolition

were placed around piers and drilled

shafts to provide continuity of the

MN pot bearings and are among the

scour protection system.

largest bearings of their type in North

FOUNDATION

AND

America. One of each of these large

bearings was tested at the US National

SUBSTRUCTURE

Testing

Laboratory

near Washington,

DC.

The new Acosta Bridge is supported

The cantilevers were erected by bal-

on 1.5 m diameter drilled shafts with 7

anced

cantilever

construction. The

to 8 shafts per back span support, and

cantilever was limited to about one-

31 and 22 shafts for each of the two

half of a segment out of balance

main piers making a total of 82 shafts

through the entire casting process to

per bridge. An extensive test program

minimize the unbalanced moments.

utilizing 900 mm test shafts was used

A stability system was required to sup-

to check capacities. Testing involved

port the out of balance moment. This

the use of sister bar strain gauges,

system consisted of three 1.1m

Osterburg cells, telltales and a wire

diameter concrete filled steel pipes

line to measure stresses and

with 15.9 mm walls. One support was

movements. The use of the Osterburg

located under each web of the box.

hydraulic cell was innovative for this

Grout pads on the footing provide

type of equipment, being applied in a

lower support for this system. These

silty clay marl to determine end bear-

pipes served as compression posts on

ing capacity.

each side of the column 4.9 m from the

center of rotation. At the top of each

Waterline footings were constructed on

the drilled shafts using a ring support

post, a sand jack with a concrete

bolted to each drilled shaft. With the

wedge was placed to provide the con-

rings in place, a 230 mm thick precast

nection under the pier table bottom

seal slab was set. A top yoke support

slab.

system was then used to support the

Superstructure

footing side forms. A 460 mm to 530

mm seal was then placed, enabling the

The river crossing is a five-span

removal of 1 m of water from the

forms. The footing, column and cap

continuous structure composed of a 67

were then constructed with

conven-

m back span, 110 m side span, 192 m

tional cast-in-place methods.

main span, 83.8 m side span and a 48.8

m back span. The superstructure

Due to physical restraints, and in an ef-

fort to minimize the size of the founda-

utilized cast-in-place segmental con-

tions, the designer used pot bearings to

struction with a typical box section

support the bridge at all pier locations.

measuring 23.10 m wide at the deck

The larger of the two cantilevers was

(Fig. 24). The box girder out-to-out

erected on three 53.4 MN fixed pot

width of 14.94 m consists of two cells

bearings. The second antilever bearing

and three web walls. The depth of the

system consists of three guided 38.7

boxes varies from 3.66 m at mid-span

Fritz Leonhardt proposed a cable-

1200 m. All problems found

stayed solution in 1968-1970 for cross-

appropriate solutions, illustrating the

ing the Messina Straits with two

fantastic possibilities of cable-stayed

pylons in the sea and a main span 1300

bridges, but navigation requirements

m long. He was followed by Rene

finally called for a 1624 m long main

Walther, who proposed that concrete

span, longer that the longest suspended

cable-stayed bridges can be economi-

span in the world, and the cable-stayed

cally built up to 600 m, and composite

solution was abandoned.

ones up to 800 m.

It is now interesting to compare the

Recent Progress

cable-stayed bridges which held the

successive world records:

- Saint-Nazaire Bridge, 1975: steel

The preliminary design of the Nor-

orthotropic box-girder ...

mandie Bridge - called the Honfleur

- Barrios de Luna Bridge, 1983:

Bridge at the time - was developed be-

prestressed concrete bridge

tween September, 1986 and Spring,

-

Anacis Bridge, 1986:

1987. The project was presented in the

composite deck with two I-shaped

first conference devoted to cable-

beams and a concrete sfab

stayed bridges, in Bangkok, in Novem-

-

Ikuchi Bridge, 1991:

ber 1987.

steel main span (and concrete access

Since that time, the world record pro-

spans, like the Normandie Bridge)

gressed with two bridges designed and

made of two parallel box-girders

built very quickly, probably helped by

-

Skarnsund Bridge, 1991: prestressed

the Normandie Bridge project, which

concrete

psychologically opened the way for

- Yangpu Bridge, 1993: composite

very long spans: the Skarnsund Bridge

construction

in Norway (530 m in November,

- Normandie Bridge, 1994: steel

1991), and the Yangpu Bridge in

orthotropic box-girder for its main

Shanghai, China (602 m in October,

span.

1993). Two other projects were clearly

The cycle is closed, and a concrete ca-

inspired by « the Normandie Bridge:

ble-stayed bridge with a main span of

the Honshu Shikoku Bridge Authority

about 1000 m cannot be expected; nor

decided,

after

the

Bangkok

probably a composite one due to high-

Conference, that the Tatara Bridge

er weight and increasing costs of ca-

would not be a suspension bridge, but

bles. But the competition which exist-

a cable-stayed one. Its erection began

ed during twenty years between con-

in 1993, and it will become, in 1998 or

crete, composite and steel decks is an-

999, the new world record with its

other indication that the limits have not

main span 890 m long. Danish

have reached.

engineers designed a new cable-stayed

MAIN ASPECTS OF THE

to be adapted to both concrete and

DESIGN

steel structures, since the deck is in

prestressed concrete in the access

While the Normandie fridge is likely

spans (Fig. 26) and in steel in the

be surpassed by even longer bridges in

central part of the main span (Fig. 27).

the years to come - the Tatara Bridge

and still longer ones very soon there-

after - it is of major importance in the

technical evolution of long-span

bridges. It is the first cable-stayed

bridge entering the domain of very

long spans, which was reserved up to

now for suspension bridges. For this

reason, it is worth pointing at the most

important aspects of its design.

Fig. 26

inverted Y to concentrate the higher

Fig. 27

anchorages of ables on the bridge

longitudinal axis.

- A high torsional rigidity, to clearly

- The shape of the pylon - an inverted

separate the vibration periods in

Y - is also extremely efficient at

torsion and vertical bending. For this

resisting transverse wind forces (Fig.

reason, the deck is a box girder

28).

suspended on both sides. In addition,

Fig. 28

the

pylons have

the shape of an

-

The

concrete

and

steel

composite

Fig. 29

deck, with concrete access spans on

Composite Construction

close supports extended at a distance

The second major point in the design

of 116 m from each pylon in the

of the Normandie Bridge is the combi-

central span, as well as the rigid

nation of prestressed concrete and

connection between deck and pylons,

steel. Composite designs, where con-

increases the structure's rigidity. Wind-

crete and steel are used to their greatest

induced

deflections

are

drastically

efficiency, are strongly endorsed by

reduced. Alan Davenport compared the

the designers of the Normandie Bridge.

deformability of the Normandie Bridge

The Normandie Bridge combines con-

with the Littlebelt suspension bridge -

crete and steel for the design of the

also efficiently built with a streamlined

deck, prestressed concrete in the access

deck based on the English experience

spans, on close supports, with an

and a main span of only 600 m - and

extension in the main span on both

concluded that the Normandie Bridge

sides. Only the central part of the m, in

behaves like a cable-stayed bridge with

span is an orthotropic steel box girder,

a much shorter main span and is much

much lighter (9 t/m, instead of the

more rigid than a suspension bridge

usual 45 t/n) to limit the cable size.

with a span of 500-600 m.

The use of concrete in the access spans

reduces total costs and increases the

bridge's rigidity, as well as the back

staying efficiency of all rear cables.

This efficient combination of concrete

in using different weights for a specific

divided into two half-elements) to be

structural purpose proved to be ex-

lifted by the site crane (capacity: 20 t),

tremely useful (the bridges at

and welded on site. The typical

Ottmarsheim and Tricastin and the

element was designed to anchor a pair

cable-stayed bridge over the Elorn

of cables on each side. The main plates

River).

were divided in ties for the transfer of

The Normandie Bridge also uses a

forces from the main span to back-

composite design for the upper part of

stays in order to lighten the elements,

the pylons, where cables are anchored

reduce in situ welds and facilitate

(Fig. 29). It is far more efficient to de-

access from the lateral cells of the

sign a steel anchorage box to anchor

pylon - with a lift - to the anchorages.

the cables, since steel plates easily car-

High Performance Concrete

ry tensile stresses from back-stays to

cables suspending the main span. In

addition, it is much easier to fabricate

The main advantage of high perfor-

these steel anchorage boxes - or the

mance concrete for standard and

elements which will constitute them -

medium span bridges is substantially

in a factory than on site in concrete

enhanced durability. But for heavily

100 or 200 m above ground. To

loaded elements, such as the pylons of

achieve the proper geometry, it is

cable-stayed bridges with long spans,

necessary to precisely adjust the

or the concrete deck of the Normandie

position of steel elements ants which

Bridge, which has to balance high

are later completed by concrete walls.

stresses from wind effects, high perfor-

Probably the first application of this

mance concrete has great structural

technique was in Belgium, for the

advantages.

construction of the Ben Ahin and

All concrete on the Normandie Bridge

Wandre Bridges, designed by Rene

contains silica fume for a characteristic

Greisch ond Jean-Marie Cremer. The

strength of 60 MPa. This allowed for a

idea was used again for the Evripos

reduction in the cross section of the

Bridge in Greece and for the Chalon-

concrete in the pylons and deck and

sur-Saone Bridge in France. The

thus a reduction in weight and founda-

problem was more complex in the

tions.

Normandie Bridge, with the transverse

Erection of the Access Spans

inclination of cables. A design was

developed with Jean-Claude Foucriat,

introducing horizontal prestressing

The erection of access spans on both

tendons to press the concrete walls

banks required the contractors to de-

against the steel anchorage boxes to

velop a new technology. Classical

help the transfer of vertical forces from

erection techniques, with Teflon pads,

steel to concrete.

would have produced very significant

The steel anchorage tower was divided

horizontal forces due to friction (up to

into 21 elements (the lower one being

5%) and to the slope of the access

ramp (6%). For this reason the initial

measurements obtained by sensors or

design did not use the incremental

video cameras.

launching method, although it was of

Erection of the Main Span

great interest due to the complex cross

section shape and to the high rein-

forcement ratio necessary to resist

The 116 m long concrete cantilever

wind forces.

which extends the side spa is in the

To be able to use it despite the slope,

main one on each bank, and the 96 m

the contractors invented a so-called

long last side span have been built by

«staircase» method for horizontal span

the balanced cantilever method from

launching. The deck is supported on

the pylon with the help of temporary

each pier by two trapezoidal blocks -

stays. In the last side span, the closure

one on each side - which can slide

was made 6 m before r 'aching the

horizontally on the pier. This

pier

with

the

incrementally

movement is permitted by special

launched typical spans.

bearings, made of a series of small

The steel part of the main span, 624m

rollers, on top of the pier. After the

long, has been erected by the

forward movement, the deck is lifted

cantilever method from the completed

by jacks commanded from a central

access spans with the help of a mobile

computer and the trapezoidal blocks

derrick to lift the successive segment

are pushed backwards, ready for a new

19.6

m long, on

each bank.

launching step. The launching opera-

A New Generation of Cables

tion proceeds by successive launching

steps: 15 cm horizontally and then 9

mm vertically to correspond to the

The preliminary design called for

slope of 6%.

locked coil cables, which were consid-

Such a procedure was only made

ered very well adapted to such long

possible by the use of a series of

spans, but which arc unfortunately

sensors, to control horizontal and

very heavy. Their erection cost thus

vertical movements on all supports,

proved prohibitive.

and of a central microcomputer which

For this reason, the contractors pro-

could command horizontal and vertical

posed alternative cables made of indi-

movements. It was of special

vidually protected strands of hot-dip

importance, of course, that vertical

galvanised wires which were re-drawn

movements be the same on all supports

to keep all their structural characteris-

at any time.

tics. After coiling and after the corre-

In addition, this new technique reduces

sponding thermal treatment, the voids

the

necessary manpower

during

between wires were filled with oil wax

launching, since control is only n

to repel any water. The strand was then

necessary at supports, which can be

protected by extruded high density

dome

at the central command

from,

polyethylene at least 1.5 mm thick.