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C urrently, the PCI is undergoing major reorganization and is
beginning to head in anew direction. But these changes can only
guide and point to what needs to bedone to revitalize our industry.
Ultimately, the success we achieve will depend upon theindividual
talent and motivation of management and all persons within the
individualcompanies to implement the suggestions, ideas, materials
and services provided by PCI.The output of PCI staff and committees
is only the beginning and is useful and importantin the process of
accomplishing our goal for a larger Market Share. Thereafter, it
will beup to the individuals to provide the spark necessary for the
companies to aggressivelycarry through the required programs.
As individuals, all of us strive for recognition for the job we
are doing whether thiscomes in the form of a pat on the back, a
kiss from the spouse, a salary increase, or anaward or commendation
from our peers. PCI over the years has provided a large array
ofprestigious awards in various categories to recognize excellence
within the industry:
Annual Awards Program to recognize professionals who have
designedoutstanding buildings, bridges and other structures.
Harry H. Edwards Industry Advancement Award for new concepts.
products,processes, designs, methods, and ideas that will benefit
our entire industry.
Martin P. Kom, Robert J. Lyman and State-of-the-Art Awards for
best authored PCIJOURNAL papers.
Certificates of Merit for outstanding PCI committee
accomplishments. Plant Certification Awards for quality procedures
and products. Safety Awards for best safety records in precasting
plants. Gale M. Spowers Awards for marketing ideas. Associate
Member Award for exceptional company services to the industry.
Architectural Student Awards. Medal of Honor Award for an
outstanding leader in the industry.These awards provide some of the
incentive to individuals in our industry for the
considerable challenges that lie ahead. The recognition is a
small token of ourappreciation to the individuals, groups, and
firms that have committed themselves to abetterment of our
industry.
PCI JOURNALISeptember-October 1987 21
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Awards Jury and PCI Officers (I-r): Terence J. Williams, FRAIC,
Ted J. Gutt, PCI Chairman of theBoard, Dirk Lohan, Donald J. Hackl,
FAIA, Clellon Loveall, Thomas B. Battles, PCI President, R.E.
Stotzer, Jr., Dan Barge, Jr., and Dan Fleming.
1987 Pul ProfessionalDesign Awards Program
Fourteen outstanding projects werenamed winners in the 1987 PCI
Pro-fessional Design Awards Program. In ad-dition, five other
projects received spe-cial jury awards. A total of 151 entries
(di-vided into ten categories) were reviewed.
The purpose of the design awards pro-gram is to recognize design
excellence inthe use of precast prestressed concreteand/or
architectural precast concrete. Thewinners are selected on the
basis of ex-ceptional achievement in aesthetic ex-pression,
function and economy, as well asingenuity in the use of materials,
methodsand equipment. Because the design prob-lems faced by
architects and engineers areso diverse, no single first place award
isgiven. Each winning project is given equalrecognition for
excellence. The special juryaward is given to projects which
display anhonorable mention level of achievement.
Seven prominent architects and engi-neers comprised this year's
jury; four onbuildings and other structures, and threeon bridges.
Jury chairman was Donald J.Hack /, FAIA, president, American
Institute
of Architects and principal, Loebl,Schlossman and Hackl,
Chicago, Illinois.Assisting Mr. Hackl were Dan Barge,
Jr.,president, American Society of Civil Engi-neers and principal,
Barge, Waggoner,Sumner & Cannon, Nashville, Tennessee;Dirk
Lohan, president, Lohan Associates,Chicago, Illinois; Terence J.
Williams,FRAIC, president, the Royal ArchitecturalInstitute of
Canada and partner The WadeWilliams Partnership, Victoria, British
Co-lumbia. For bridges, R. E. Stotzer, Jr., en-gineer director,
State Department of High-ways & Public Transportation,
Austin,Texas; ClelIon Loveall, assistant executivedirector,
Planning and Development, De-partment of Transportation, Nashville,
Ten-nessee; and Dan Fleming, director, Officeof Bridges and
Structures, Department ofTransportation, St. Paul, Minnesota.
The designers of the winning projectswere honored during award
ceremonies atthe 1987 PCI Convention in New Orleans,Louisiana on
October 20. Descriptions, to-gether with jury comments, of each
win-ning project follow.
22
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The Hyatt Regencyat Greenwich, Connecticut
Architect: Kohn Pedersen Fox Associates. PC, New York, New
York.Structural Engineer: Lev Zetlin Associates, New York, New
York.Construction Manager: Turner Construction Co., Norwalk,
Connecticut.Precast Prestressed Concrete Manufacturer: Pre-Con
Company, Brampton, Ontario,
Canada.Floor Slab Manufacturer: Coreslab Limited, Burlington,
Ontario, Canada.Owner: The Hyatt Development Corporation, Chicago,
Illinois.
S everal design challenges existed in constructing this luxury
hotel. First, afterdeveloping a design concept which complemented
the image and quality of thelocal community, the architects needed
to use a material which allowed for a highlevel of detail but which
fell within a reasonable budget. Secondly, the height of
thestructure was set by the local zoning ordinance at 48 ft (14.6
m). Thirdly, theconstruction schedule required that the building be
completed within five months.
All these considerations were uniquely met by utilizing precast
concrete andinnovative design and construction strategies. The
precaster and architect workedtogether to resolve the intricacies
needed to mold the details for such items as the infillbrick, the
Tuscan arches at the entry, and the atrium's tripartite
columns.
Jury Comment: "This luxury hotel is a good example in showing
how architecturalprecast concrete panels can be blended
attractively with brick to produce a building thatportrays a warm,
rich, light and airy feeling."
PCI JOURNAL1September-October 1987 23
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Olympic OvalCalgary, Alberta
Prime ConsultantlArchitect, GrahamMcCourt, Calgary,
Alberta.Structural Engineer: Simpson, Lester, Goodrich, Calgary,
Alberta.General Contractor: W. A. Stephenson Construction (Western)
Ltd., Calgary, Alberta.Precast Prestressed Concrete Manufacturer
and Post- Tensioning: Con-Force
Structures Ltd., Calgary, Alberta.Owner: The University of
Calgary, Calgary, Alberta.
p recast prestressed concrete arch and perimeter beam segments
provided themajor structural strength for the roof of this gigantic
Olympic speed skating ovaland athletic and recreational fieldhouse.
The diagonally intersecting arch systemallowed the building shape
to precisely reflect the shape of the speed skating track.Because
of the curved faceted roof shape and low perimeter height. there is
noundesirable visual impact on the surrounding campus.
Jury Comment: "A superbly engineered structure which is also
aesthetically pleasing.The roof seems to float effortlessly,
creating a light airy comfortable feeling."
24
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Commissioners of Public WorksAdministrative OfficesCharleston,
South CarolinaArchitect: Lucas Stubbs Pascullis Powell &
Penney, Ltd., Charleston, South Carolina.Structural Engineer:
Johnson & King Engineers, Inc., Columbia, South
Carolina.General Contractor: D.R. Allen & Son, Inc.,
Fayetteville, North Carolina.Precast Prestressed Concrete
Manufacturer: Arnold Concrete Products, Raleigh,
North Carolina.
A bout 350 architectural precast concrete panels in varying
sizes were used to cladthis office building situated in a
residential neighborhood. The precast concretewas designed to give
the appearance of wood clapboard. The total effect of thedetailing,
plus the efficient cooperation of the precaster, resulted in a
magnificent jobtotally true to the original concept.
Jury Comment: "The design uses precast concrete in a very
innovative way, bringingthe material down to a scale that is
clearly residential and yet it also complements thefabric of the
neighborhood."
PCI JOURNAL/September-October 1987 25
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1700 California StreetSan Francisco, California
Architect: Jorge de Quesada Inc., Architects, San Francisco,
California.
Structural Engineer. Raj Desai Associates, Inc., San Francisco,
California.
General Contractor: Williams and Burrows General Contractors,
Belmont, California.
Owner: American Savings, San Francisco, California.
G lass fiber reinforced concrete (GFRC) was selected as the most
suitable material to clad this prestigious ten-story building which
combines retail, office space andresidential condominiums. Nearly
1000 GFRC panels with granite inlays and greenglass were used to
conform 10 the complex articulation of the building's facade.
Thelightweight panels were easy to install and contributed to an
aesthetically pleasing,structurally safe and cost effective
building.
Jury Comment: "This is a high tech solution to the use of
precast concrete in amarine environment. We particularly liked the
interplay of the blue, green and whitecolors,"
26
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Residence for Mr. and Mrs. Hans KeilhackCharlotte, North
Carolina
Architect: Gene Leedy, Architect, Winter Haven,
Florida.Builder., Hans Keilhack, Keiltex Corporation, Charlotte,
North Carolina.Precast Prestressed Concrete Manufacturer: Exposaic
Industries, Charlotte, North
Carolina.
Owner: Hans Keilhack, Charlotte, North Carolina.
recast columns, beams, double tees and lintel beams formed the
shell of this handsome residence. The structure was designed for a
couple who entertainquite often and is built on a 30-acre wooded
hill site overlooking a large lake. Thestructural system was left
exposed for aesthetic considerations.
Jury Comment: The architect and owner really thought of precast
concrete as abuilding material from the outset because the
discipline is apparent. The home iswarm and inviting, and the
structure has grandeur. We particularly liked the strengthof the
horizontal precast beams as contrasted with the presence of the
trees."
PCI JOURNAL/September-October 1987 27
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Lincoln PlazaSacramento, California
Architect: Dreyfuss Blackford Engler Architects, Sacramento,
California.Structural Engineer: Buehler & Buehler Associates
Structural Engineers, Inc.,
Sacramento, California.
General Contractors: NVE Constructors, Inc., Sacramento,
California, & the M. M. SundtCorporation, Phoenix, Arizona.
Precast Concrete Manufacturer: Tecon Pacific, West Sacramento,
California.Owner: California Public Employees' Retirement System,
Sacramento, California.
ome 2000 architectural precast panels and trellis members were
used to clad thisfive-story headquarters office building. The
panels and trellis members were cast
with the same delicate warm gray concrete mix as the exposed
concrete columns andbeams, thereby presenting a complete and
unified building theme based on theintricate texture of these
exposed surfaces.
Jury Comment: "This building makes a significant contribution to
the civic setting notmerely because of its scale but because it
creates an exciting and stimulating workingplace environment."
28
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Stevenson Place, San Francisco, CaliforniaArchitect:
Kaplan!McLaughlin/Diaz. San Francisco, California.Structural
Engineer: Cygna Consulting Engineers, San Francisco,
California.Contractor. Cahill Construction, San Francisco,
California.Owner: Tishman West Management Corp., San Francisco,
California.
orne 2000 architectural precast concrete panels with 600
different configurationswere used effectively to clad this
distinctive 23-story office building set in San
Francisco's financial district. A special design feature was the
integration of polishedgranite into the precast panels. Reveals 11
1/2 in. (38 mm) deepI at the junction betweenthe panels and stone
not only animate the appearance of the facade but also help maskthe
panel joint.
Jury Comment: "The facade of this building is carefully detailed
with the granite backedpanel well integrated into the overall
design. The building is a handsome addition to thecity's
skyline."
PCI JOURNAUSeptember-October 1987 29
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Stanford University ParkingStanford, California
Architect & Engineer: The Watry Design Group, Redwood City,
California.General Contractor: C. Overaa & Company, Richmond,
California.Owner: Leland Stanford Jr., University, Stanford,
California.
A major feature of this 1064-car five-level university parking
structure is thedistinctive architectural precast concrete
railings. Built to resist high impact
loads, the rails were designed with gentle curves to allow the
structure to "flow" andindicate vehicle traffic behind them. The
serrations, indentations, and color of the railsgive texture, scale
and beauty to the parking structure.
Jury Comment: "The architectural treatment of the facade of this
parking structure isunique. In particular, the fractured rib
texture of the railings is beautifully thought out."
30
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Arkansas Valley Correctional FacilityOrdway, Colorado
Architect: RN. L. Design, Denver, Colorado.Structural Engineer.,
S.A. Miro, Inc. : Denver, Colorado.General Contractor: G.E. Johnson
Construction Company, Colorado Springs,
Colorado.Precast Prestressed Concrete Manufacturer: Stanley
Structures, Denver, Colorado.Owner: State of Colorado, Department
of Corrections, Colorado Springs, Colorado.
P recast concrete was used extensively to build this 742-bed
medium securityprison. Because of the repetitive characteristics of
the housing units, precastConcrete proved to be the ideal material.
Yet there was enough variation and color in theelements to give the
facility the desired humanizing environment. The project utilized
afast track construction technique to meet critical deadlines and
economic restrictions.
Jury Comment: "This structure represents the most integrated use
of precastconcrete we have seen. It is a humane facility
refreshingly different from thetraditional type of prison."
PCI JOURNAUSeptember-October 196731
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Olin Library, Kenyon CollegeGambier, Ohio
Architect: Shepley Bulfinch Richardson and Abbott, Boston,
Massachusetts.General Contractor: The Albert M. Higley Company,
Cleveland, Ohio.Precast Concrete Manufacturer: Masolite Concrete
Products, Inc., Fort Wayne,
Indiana.
A rchitectural precast concrete was beautifully conceived in
cladding this smallcollege library. The smooth horizontal banding
and window trim contrasts withthe rough finish of the exposed
aggregate surface in the same manner that themolded stone banding
contrasts with the rough cut stone on many of the
surroundingbuildings. The panels were erected at a rapid rate and
the job proved to be costeffective.
Jury Comment: "Precast concrete is used in a rather novel way.
The architecturalconcrete is done very cleanly, is sharp and crisp
with beautiful detailing."
32
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Special Jury Award
Brandywine Shoal LighthouseDelaware Bay, New Jersey
Design Engineer: Duffield Associates, Wilmington,
Delaware.Construction Engineer: Gredell & Paul, Wilmington,
Delaware.General Contractor: Page Hill Corporation, Winterport.
Maine.Owner: United States Coast Guard, Shore Maintenance
Detachment,
Governors island, New York.
recast concrete was selected as the most durable material to
structurallyrehabilitate this historic and still functioning
lighthouse which annually guides
some 3000 ocean-going vessels along a hazardous shipping
channel. Severelydeteriorated components that supported and covered
the first level deck werereplaced by ornate precast components
which included brackets, columns andcornice segments.
Jury Comment: 'This is an imaginative and surprising application
of precastconcrete. The project appealed to the romantic side of
the judges. It shows thatprecast concrete can be used in a hostile
environment where other materials woulddeteriorate."
Design engineering was performed by principals of Gredell &
Paul, who formed theirown firm upon completion of construction
documents.
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Special Jury Award
Tom Bradley International TerminalLos Angeles, California
Architect: Pereira Dworsky Sinclair Williams, Los Angeles,
California.
Structural Engineers: Brandow & Johnson Associates, and
Sinclair & Associates, LosAngeles, California.
Contractor: Tutor-Saliba-Perini J. V., Sylmar, California.
Precast Prestressed Concrete Manufacturer: Rockwin Corporation,
Santa FeSprings, California.
Owner: Los Angeles Department of Airports, Los Angeles.
California.
A rchitectural precast concrete was used extensively to clad
this international airlineterminal. The precast panels provide a
durable and attractive finish, and alsoallow for precise
dimensional quality and control. The use of concrete panels alsowas
beneficial to the team in meeting the stringent construction
schedule.
Jury Comment: "Considering the enormous scale, this is a very
straightforward anddirect use of precast concrete and this building
carries it off very well."
34
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Special Jury Award
Ten Central Car ParkKansas City, MissouriArchitect: Patty
Berkebile Nelson Immenschuh Architects, Kansas City, Missouri.
Structural Engineer: Norton and Schmidt Consulting Engineers.
Kansas City,Missouri.
General Contractor: Dasta Construction Company, Kansas City,
Missouri.
A large variety of precast prestressed concrete components were
used to framethis three-level 410-car parking structure located in
a central business district.To complement adjacent buildings,
limestone-toned precast concrete panels withdeep-set reveals were
used on the exterior. The structural system comprised
precastcolumns, bearing walls, double tees and other
components.
Jury Comment: `The design of this parking structure is well
integrated with thebuilding adjacent to it while at the same time
it makes excellent use of precast andprestressed concrete."
PCI JOURNAL/September-October 1987 35
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Sunshine Skyway BridgeTampa Bay, Florida
EngineerlDesigner: Figg and Muller Engineers, Inc., Tallahassee,
Florida.Owner: Florida Department of Transportation, Tallahassee,
Florida.Contractors: Paschen Contractors, Inc., Chicago,
Illinois/American Bridge, Chicago,
Illinois/Morrison-Knudsen, Boise, Idaho. Joint
Venture.Consultant to Paschen Contractors: J. H. Pomeroy & Co.,
lnc.IPomco Associates, Inc.,
Port Manatee-Palmetto, Florida.
his 4.14 mile (6.7 km) long precast prestressed segmental box
girder bridge isrecognized for its many design innovations and
advanced construction
techniques. The 1200 ft (366 m) main span is one of the longest
cable stayed spans inthe world and comprised some of the largest
match cast segments ever fabricated.For so large a project, the
quality of the precasting, the dimensional accuracy andgeometric
control of the segments, and speed of erection are unexcelled.
Jury Comment: "This precast prestressed cable stayed bridge is a
superblyengineered structure which is destined to have a profound
impact on the futurepractice of bridge construction across North
America."
U
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Richard P. Braun BridgeMississippi River BetweenCoon Rapids and
Brooklyn Park,Minnesota
Architect/Engineer: Minnesota Department of Transportation, St.
Paul, Minnesota.General Contractor: Park Construction Company,
Fridley, Minnesota.Precast Prestressed Concrete Manufacturer: Elk
River Concrete Products,
Minneapolis, Minnesota.
Owner: Minnesota Department of Transportation, St. Paul,
Minnesota.
P recast prestressed concrete I girders were selected for this
eleven-span highwaybridge situated in a suburban park near
Minneapolis primarily for the economyoffered by the repetitive use
of prestressed components. Simultaneously, thefunctional, long-term
maintenance costs and aesthetic requirements of this facilitywere
amply satisfied. A total of eighty-eight 81 in. (2057 mm) deep
Minnesota girderswere used at spans ranging from 111 to 122 ft (34
to 37 m).
Jury Comment: "The prestressed girders blended beautifully with
the concretesubstructure, deck slab and railings to create a bridge
with clean efficient lines. Thestructure is an aesthetically
pleasing addition to the park system."
PCI JOURNAL/September-October 1987 37
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L fr 4 &:i
Research Boulevard BridgeKettering, OhioEngineer: Harold D.
Jones, Lockwood, Jones & Beals, Inc., Dayton, Ohio.Architect:
Edward Durell Stone, New York, New York.Consulting Architect:
William E. Wells, California Department of Transportation,
Sacramento, California.Contractor: Fratz Brothers Construction
Company, Sidney, Ohio.Precast Prestressed Concrete
Manufacturer:
Fascia Panels: Concrete Technology, Springboro, Ohio. Bridge
Beams: Prestress Services, Inc., Decatur, Indiana.
Owner: Tom Stabler, City of Kettering, Kettering. Ohio.
recast prestressed concrete box beams with architectural precast
fascia panelswere selected for this three-span 192 ft (58.6 m) long
highway bridge located at a
distinguished research park. The exposed aggregate, concrete
color and finish oT theprecast panels were chosen carefully to
blend with the panels on surroundingbuildings. In addition, the use
of recessed pier caps and set-back columns enhancedthe long
horizontal lines of the structure.
Jury Comment: "The combination of architectural and structural
precast concreteblended admirably with the surrounding buildings
and park environment."
38
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University BridgeMississippi River atSt. Cloud,
MinnesotaArchitect/Engineer: Howard Needles Tammen &
Bergendoff, Minneapolis,
Minnesota.General Contractor: Lunda Construction Company, Black
River Falls, Wisconsin.Precast Prestressed Concrete Manufacturer:
Elk River Concrete Products,
Minneapolis, Minnesota.Owner: City of St. Cloud, St. Cloud,
Minnesota
To keep costs down, precast prestressed concrete girders
together withcantilevered pier tables were used effectively to
build an eight-span 1167 ft (356 m)roadway bridge adjacent to a
college campus and park. By post-tensioning the piertables, it was
possible to achieve longer than usual span lengths, keep down the
numberof spans and piers, and allow for future expansion of the
structure. The 63 and 81 in.(1600 and 2057 mm) deep girders ranged
in length from 107 to 136 ft (32.6 to 41.5 m). Atotal of 63 beams
were required.
Jury Comment: "This is an imaginatively engineered bridge which
is alsoaesthetically pleasing. Structural continuity between the
prestressed girders and piertables creates smooth graceful
lines."
PCI JOURNALSepternber-October 1987 39
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Special Jury Award
Lightfoot Mill RoadSouth Chicamauga CreekHamilton County,
TennesseeStructural Engineer: Division of Structures, Tennessee
Department of Transportation,
Nashville, Tennessee.Contractor: Highland Construction Company,
Cleveland, Tennessee.Precast Prestressed Concrete Manufacturer:
Ross Prestressed Concrete, Knoxville,
Tennessee.Owner: Tennessee Department of Transportation,
Nashville, Tennessee.
T his four-span 390 ft (119 m) long highway bridge is unique in
that the precastprestressed concrete beams are designed to be
integral with all substructuresrather than only continuous. In
addition, the bridge is integral for all live loads and
isconstructed with no expansion joints to create a structure with
almost nomaintenance.
Jury Comment: "A creative solution to a frequent problem which
simultaneouslyresulted in an aesthetically pleasing and economical
bridge."
40
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Special Jury Award
Harbor Street Grade SeparationPittsburg, California
Designer: CH2M Hill, Emeryville, California.Precast Prestressed
Concrete Manufacturer: J. H. Pomeroy and Company, Inc.,
Petaluma, California.
Owner: City of Pittsburg, Redevelopment Agency, Pittsburg,
California.
This structure, situated at the Atchison, Topeka and Santa Fe
Railway Companytracks, is a four-span, two-track railroad bridge
with a total length of 143 ft 8 in.(43.8 m). The cross section
consists of nine 4 ft deep x 3 ft 6 in. wide (1.22 x 1.07 m)precast
prestressed concrete box girders. Precast concrete allowed
rapidconstruction of the grade separation, minimizing disruption to
automobile traffic on thebusy street below.
Jury Comment: "it is refreshing to see precast prestressed
concrete used soeffectively in a railroad bridge. This type of
construction should be encouraged."
"f j 1!
1I
U A
PCI JOURNAL/September-October 1987 41
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Production and Erection ofPrestressed Concrete Poles
for a RailroadElectrification Project
Leonard G. McSaveneyChief EngineerFirth Stresscrete
DivisionFirth Industries LimitedAuckland, New Zealand
During the oil crisis of the 1970s theNew Zealand Government
com-mitted itself to doing all it could to re-duce the effect on
the country of futurerises in oil prices. One of the options atthat
time was to convert the most heav-ily trafficked section of the New
Zea-land Railways Corporation system fromdiesel powered to electric
locomotives.
In 1981 the decision was made toelectrify a major part of the
North Islandmain trunk line. While in this time oflowering world
oil prices and risingelectricity costs the initial economicsmay he
hard to justify, the long term ad-vantages of the scheme will
benefit boththe Railways Corporation and the coun-try in the
future.
The section to be electrified, throughthe center of the North
Island, contained
many steep grades through difficult ter-rain. In addition to the
savings in im-ported fuel, electric locomotives offeredthe
additional advantages of better trac-tive power on the steep
sections of track,resulting in longer trains hauling greaterloads,
increased reliability and im-proved operating efficiency.
Electriclocomotives also have the advantagethat regenerative
braking on the down-hill runs can be used to power other
Io-comotives on the system.
In 1983 bids were called worldwidefor the electrification of a
172 km (108mile) section of track using a 25,000 voltalternating
current system. This projectwas split into several contracts:
Loco-motives, Signals and Communications,and Traction Overhead
(catenary cablesand support structures). Local contracts
42
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were also let for track realignment, tun-nel alterations and
general upgrading ofthe line.
Included in the pole supply bid con-ditions was the option for
the New Zea-land Railways Corporation to extend theStage I contract
to Stage 11, a further 230km (144 miles) of track.
The contract for the Traction Over-head portion of the project,
valued atNZ$35,000,000 (US$20,000,000), waswon by a joint venture
company: Mc-Connell Dowell Constructors Ltd fromNew Zealand and
Multi ConstructionEngineering Ltd from Australia. TheMcConnell
Dowell MCE Joint Ven-ture awarded a subcontract to
FirthStresscrete, a division of Firth Indus-tries Ltd, for the
design and supply ofthe prestressed concrete poles.
Electrical SystemThe prestressed concrete poles sup-
port a combination of conductors sus-pended from a steel
framework. The25kV system comprises five conductors:the earth wire
connected to the back ofthe pole, the protection wire separatedfrom
the pole by two 3kV porcelain in-sulators, the auto-transformer
feederwire supported from a 25kV insulatorand the contact and the
catenary wiressuspended over the middle of the trackfrom a steel
tube frame with 25kV insu-Iators at its end.
All the conductors, with the exceptionof the earth wire, are
insulated from thepole's "earth potential" by the 3kVstand-off
insulator between the pole andthe rectangular hollow steel
stand-offtube. The stand-off tube allows forheight adjustments to
the cantilever armwhen registering the equipment.
Pole OptionsPreliminary discussions with the New
Zealand Railways Corporation had indi-cated that approximately
4000 poleswould be required for Stage I and a fur-
PCI JOURNAL/September-October 1987
SynopsisA long line production method for
producing prestressed concrete polesto support overhead catenary
wiresfor a railroad electrification project hasbeen developed in
New Zealand-
The method is ideally suited to pro-ducing poles economically
from aconventional multiproduct preten-sioned precast concrete
factory usingsemiskilled labor.
This paper describes the evolutionof the design concept, optimum
poleshapes, quality assurance, productionand installation
methods.
they 6000 poles for Stage II. Since thereseemed little
likelihood of further sec-tions of track being electrified, a
pro-duction process that could produce10,000 poles over a 4-year
period was allthat was required. Because of the rela-tively small
number of poles, FirthStresscrete felt that a sophisticated
spe-cial purpose factory to produce the spunhollow circular poles
that are used inother electric rail systems around theworld could
not be justified for thiscontract.
The company chose, therefore, to baseits bid on a pole that
could be manufac-hired in any of its existing prestressingfactories
along the route of the electri-fied track. The method chosen had to
fiton existing long line pretensioningbeds, be able to use concrete
from aready mixed concrete truck, and not re-quire any production
plant or laborskills that are not normally associatedwith the
production of structural precastpretensioned concrete flooring or
bridgeunits.
The bid specification provided anumber of material options for
the poles:steel, timber and concrete. All alterna-tives were
investigated by the contractor
43
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A VARIES
803.73'
A
s5 I
170 ( 8.63"1
SECTION A-A
All Holes 25 mm Die.!T'1
---I I - 250 1 9.6 .7 1 -- - - 455 1 181
NO TES AND DESIGN LOADINGSPoleLength 10.000m. (32 =
9-7)TransverseW.L. 6-80 MN (1530Ibs.)
DownLineW1. (.70 NN (380IL's.)
LoadApplied fromtopat 305 mm (?-0)
SafetyFactoratW.L. r2GroundLine 2000 mm (6"-7)
WeightofPole 1100 kg (2424 IL's)
Fig- 1. Front and side elevations, cross-sectional details,
design loadings and otherparticulars of Pole Type 510C 10 m (32 ft
9.70 in.).
44
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and the New Zealand Railways Corpo-ration, taking full account
of both theelectrical and structural properties ofthe
materials.
The final decision in favor of pre-stressed concrete was based
on thismaterial offering the most economicalsolution, together with
an aestheticallypleasing appearance when combinedwith the overhead
equipment.
Pole prices in Firth Stresscrete'sNZ$3,000,000 (US$1,700,000)
pole sup-ply contract ranged from NZ$150.00(USS84.00) per pole to
NZ$190.00(US$106.00) per pole for the typicalpoles, and up to
NZ$350.00 (US$196.00)per pole for the special poles.
Design and form costs were coveredby a separate lump sum
payment.
Design and EngineeringFirth Stresscrete is New Zealand's
largest manufacturer of precast pre-stressed concrete. The
company hasbeen designing and manufacturing pre-stressed concrete
power poles in NewZealand since the early 1950s.
Computer aided designs for a range ofdifferent poles have been
well proven inservice and by load tests.
It was decided to adapt a standard ta-pered I-section pole to
give a series ofpoles to suit the varying load and
serviceconditions. Fig. 1 shows front and sideelevations, cross
section, design load-ings and other details of a typical pole.
Each pole location is designed anddetailed for its particular
loads. Thepoles, cantilever arms and foundationsare selected to
provide the most eco-nomical solution for each location. Polesare
manufactured to various lengths andstrengths to cater for varying
groundlev-els and bending moments.
Twelve types of poles were even-tually required. These were
producedfrom five different molds. The fivemolds produced:
1. Long and short poles for straighttrack.
2. Long and short poles for curvedtrack.
3. Extra long poles for steep foun-dation sites.
4. Crossing loop poles with canti-lever arms on each side.
5. Poles to bolt on the sides ofbridges.
6. Portal poles to support steel crossbeams over several tracks
in sta-tion areas.
7. Headspan poles to support multi-ple conductors off a
suspendedcatenary wire for multiple tracksin marshalling yards.
S. Bolted base poles for use on padfootings.
9. Substation poles and overheadfeeder poles.
10. Clearance poles to raise otherpower distribution lines
abovethe main power feed wire.
All poles were designed to have com-patible strand patterns
using 12.5 mm(V in.) diameter seven wire strand, Thisenabled them
to be cast end to end onlong line stressing beds.
The poles were designed and manu-factured to New Zealand
Standard NZS3115 (1980) "Concrete Poles for Electri-cal
Transmission and Distribution."This is a performance standard
allowingany recognized concrete design methodto be used but
specifying cracking mo-ments and ultimate capacity in terms
ofdesign working loads.
The standard specifies test loadingprocedures to destruction to
prove thedesign and also load tests to workingloads as part of the
quality assuranceprocedure.
The design parameters set out in thestandard are:
1. No cracks under working loads.2. A factor of safety against
collapse of
2.0.3. A down line strength of 25 percent
of the transverse strength.4. Tip deflection under working
load
of 1150 of the height above ground.5. Minimum concrete cover to
any
PCI JOURNAUSeptember-October 1987 45
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steel reinforcement of 20 mm (0.8in.).
The only amendment to this standardwas to reduce the allowable
tip deflec-tion to limit the deflection at conductorlevel to 50 mm
(2 in.), This was done toensure that the conductor wire wouldnot be
blown off the locomotive panto-graph contact under maximum
operatingwind speeds.
Form Design and PoleProduction
An essential item in reducing produc-tion costs is an efficient
and durableform. Hinged steel forms were used thathave required
very little maintenanceafter the 700 casting days that they
havebeen in production to date.
The poles are cured by circulating hotwater through tubes built
into the forms.Insulated fabric covers are used to min-imize heat
losses. The design 28-daycylinder strength of the poles is 45
MPa(6500 psi) and transfer strengths in ex-
cess of the 28 MPa (4000 psi) minimumare achieved after 16 hours
of curing.
The factory producing the poles isalso manufacturing poles for
local powersupply authorities, flooring products forbuildings, and
bridge beams. No specialskills are called for in the production
ofthe railroad poles and no additional me-chanized equipment was
required. Theminimum equipment is one overheadcrane to strip the
poles from the moldsand a forklift to stockpile the poles andto
load the rail wagons. Production laboraverages 3 to 4 man hours per
pole andthe poles are produced at a rate of 90poles per week.
With each pole made for a specifictrack location, schedules of
poles aregiven as soon as the pole location anddesign parameters
are determined bythe main contractor and the New Zea-land Railways.
A wagon Ioading se-quence is also given for each wagon loadof
poles. This ensures that poles can beplaced from the train in the
correct se-quence.
Fig. 2. Hi-Rail crane with auger attachment prepares to excavate
a pole foundation.
46
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Quality AssurancePoles are manufactured to a rigid
quality assurance program. This startswith the design of the
product and themolds; includes quality control checkson the
component materials, the pro-duction methods, the finished
product,and transport and handling.
Part of the requirements of NZS 3115requires one pole in every
100 to be testloaded up to the design working load. Atthis load it
must have no cracks and itsdeflection must be within 15 percentof
the average deflection for all poles ofthat type tested.
The aim of the quality assurance pro-gram is to ensure that all
poles leavingthe factory are satisfactory. Remedialwork at remote
sites, often without roadaccess, is very expensive.
Pole InstallationInstallation of these poles through
particularly rugged sections of the cen-tral North Island of New
Zealand ishampered by lack of access. Often theonly access is from
the rail track. This isa single track and must be cleared forthe
passage of trains at regular times.
This problem has stretched the in-genuity of the McConnell
Dowell -MCE joint venture and has led them todevelop a novel series
of dual road-railand rail mounted machines. These ma-chines are
able to perform all the majorpole installation functions and
arequickly able to lift themselves clear ofthe track to enable
trains to pass.
The installation starts with the pas-sage of a supply train
hauling wagonloads of poles. The poles are laid along-side the
track by a hydraulic cranemounted on a rail wagon. Workmen
thendress the poles with the insulators andstand-off tube, and fit
any other specialhardware. When the poles have beenlaid out, the
foundation holes are au-gered by two rail mounted hydrauliccranes
equipped with power swivels andpendulum augers (Fig. 2). A third
rail
Fig. 3. Pole installation using rail mountedcrane.
mounted Palfinger crane (Fig. 3) followsthe auger cranes and
lifts the poles intoposition where they are temporarilybraced in
the correct alignment.
Concrete is delivered to the founda-tion holes by a
hydraulically driven railmounted truck transporter (Fig. 4).
Thistransporter is capable of carrying a fullyloaded ready-mixed
concrete truck atspeeds of up to 25 km per hour (15 milesper hour).
This machine is also able tolift itself clear of the track onto
trans-portable stands similar to those used bynormal track
maintenance machines.The concrete transporter has proven tohe so
ideal for the job that a further fivemachines have been sold for
use onAustralian railroads.
Fig. 5 shows the equipment used forrunning out the contact
wire.
The conductors were installed using arail mounted truck with a
hydraulic lift
PCI JOURNALSeptember-October 1987 47
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Fig. 4. Rail mounted concrete transporter for casting in place
pole foundations.
Fig. 5. Equipment used for running out the contact wire.
platform, as shown in Fig. 6.Fig. 7 shows the final adjustment
of
contact wire and the finished pole con-figuration.
Using the above specialized equip-ment, the joint venture's
small highlymotivated crew have been able to installpoles at a rate
of tip to 150 poles per
5-day week.The erection of the overhead con-
ductors is split into three separate oper-ations:
1. Running out and sagging of thefixed termination
conductors.
2. Running out and tensioning of thecounterweight tensioned
contact
48
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Fig. 6. Hi-Rail truck with hydraulic lift platform installing
conductors.
and catenary system.3. Registration to line and level of the
contact and catenary wires andfinal adjustment to the
cantilevers,
For each of these operations equip-ment has been developed using
bothroad-rail vehicles and modified NewZealand Railways rolling
stock.
Foundations
An economical method of overcomingvarying ground levels and soil
bearingcapacities without the need to produce awide range of
different pole lengths wasessential to reduce both the pole
pro-duction costs and the cost of foundations.
PCf JOURNAL'September-October 1967 49
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Fig. 7. Final adjustment of contact wire showing finished pole
configuration.
The solution arrived at, after exten-sive site testing, was able
to accommo-date the typical range of ground levels,and soils
varying from poorly compactedembankment fill to well compacted
soilsand soft rock, using only two lengths ofpoles.
Concluding RemarksThe choice of an I-shaped section re-
stilts in a pole that ideally matches theservice loads. The pole
is designed for
the load of wind on the wires in the di-rection transverse to
the track. In theopposite down line direction the loadcapacity of
25 percent of the transversestrength provides an adequate marginfor
handling loads, wire tensioningloads and accidental overloads.
By choosing a production method thatis compatible with the
normal range ofproducts in a typical precast prestressedconcrete
factory, the system is economicalfor small production runs in
factories thatwish to diversify their product range.
50
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The prestressed concrete poles forthis railroad electrification
project havewon the New Zealand Concrete Soci-ety's 1986
Prestressed Concrete Award.
In making this award, the judges wereimpressed by both the
structural effi-ciency of the design and the aestheticallypleasing
appearance of the slenderfluted poles. They were also impressedby
the on-going commercial implica-tions of the project. The design
andmanufacturing systems have been sosuccessful that they have been
licensedfor use in other countries.
The use of these slender prestressedconcrete poles has minimized
the in-trusion of the overhead electrificationon the predominantly
rural environmentthat the railroad passes through.
Stage I of this railroad electrificationhas been completed.
Stage II is due tohe completed by February 1988. Thesuccessful
manufacture and installationover more than 8000 poles without
aproblem is a tribute to Firth Stress-crete's production personnel
and toMcConnell Dowell MCE's fieldcrews.
NOTE: Discussion of this article is invited. Please submityour
comments to PCI Headquarters by June 1, '1988.
PCI JOURNAL/September-October 1987 51
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Special Report
Cable Stayed BridgesWith Prestressed Concrete
Fritz LeonhardtProf. Dr. Ing.Consulting EngineerStuttgartWest
Germany
T he number of cable stayed bridgeswith concrete or steel has
increaseddramatically during the last decade. Ref.1 presents a
survey of some 200 cablestayed bridges that have been designedor
built throughout the world,
Although most of these bridges aremade of steel, many of them
could havebeen designed with prestressed con-crete. In fact, by
using this material, thedesign, structural detailing and
construc-tion method can be simplified, thus pro-ducing a bridge
that is economically andaesthetically superior.
Unfortunately, there are many bridgeengineers today that do not
fully under-
Note: This paper is based upon the Keynote Lee-hire presented by
the author at the FTP Congress inNew Delhi, India, February 16,
1986, and a similarlecture, including steel bridges, at the
Symposiumon Strait Crossings in Stavanger, Norway, in Oc-tober
1986.
stand the basic principles of cable staybridge design and
construction. Thepurpose of this article is to present thelatest
state of the art on cable stayedbridges while elaborating upon
thefundamentals and possibilities pertain-ing to such structures.
The text willcover highway, pedestrian and railroadbridges using
prestressed concrete.
1. Range of Feasibility ofCable Stayed Bridges
There are some misconceptions re-garding the range of
feasibility of cablestayed bridges. For example, the state-ment is
often made that cable stayedbridges are suitable only for spans
from100 to 400 in (about 300 to 1300 ft). Thisstatement is wrong.
Pedestrian bridgeswith only about 40 m (130 ft) span can bebuilt to
be structurally efficient and cost
52
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Based on his more than 50 years of experience as aconsulting
engineer on specialized structures, theauthor presents a state of
the art report onprestressed concrete cable stayed bridges
withauthoritative advice on the design-constructionintricacies
involved with such structures.
effective. Employing prestressed con-crete, the superstructure
can be madevery slender using a few cable stays anda deck with a
depth of only 25 to 30 cm(10 to 12 in.).
Highway bridges can be built of pre-stressed concrete with spans
up to 700 in(2295 ft) and railroad bridges up to about400 m (1311
ft). If composite action be-tween the steel girders and a
concretedeck slab is utilized, then spans of about1000 and 600 in
(3279 and 1967 ft) forhighway and railroad bridges, respec-tively,
can be attained safely.
For the crossing of the Messina Straitsin Italy (see Fig.1), our
firm designed anall-steel cable stayed bridge with a mainspan of
1800 m (5900 ft) for six lanes ofroad traffic and two railway
tracks with-out encountering any structural or con-struction
difficulties.
Many bridge engineers believe thatfor spans above 400 m (1311
i), a sus-pension bridge is preferable. This as-sumption is false.
In fact, a cable stayedbridge is much more economical, stifferand
aerodynamically safer than a com-parative suspension bridge. The
author
Fig. 1. Messina Straits Bridge, linking Sicily and Italian
peninsula; design by GruppoLambertini (1982).
PCI JOURNALISeptember -October 1987 53
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hSuspension Bridge
Cable stayed Bridge"h t. t 5
weight t
50000width of bridge 38m
46 000 t
1.0 Gip 1
46 000 = 240
30 000 f9 200
0
12300.2.16 yQ
20? 0005 70oL,^e ^\rQ 19 2DD t
1z 30oapt`'
1;^ ocio i5, e
5 700
0500'100015001800mspan
Fig. 2. Comparison of quantity of cable steel for suspension
bridges andcable stayed bridges.
showed this was true as early as 1972)In designing a cable
stayed bridge
there is first the problem of finding therequired quantity of
high strength steelfor the cables. For a bridge with a 1800m (5902
ft) main span and 38 m (125 ft)width, a suspension bridge needs
46000t (50700 tons) of steel whereas a cablestayed bridge only
needs 19200 t (21170tons) of steel (see Fig. 2). In the lattercase
this represents only about 40 per-cent the amount of steel.
Furthermore, a suspension bridgeneeds a stiffening girder with a
bending
stiffness which must be about ten timeslarger than that of the
cable stayedbridge. The suspension bridge needsadditional heavy
anchor blocks whichcan be extremely costly if the
navigationclearance is high and foundation condi-tions are poor.
The total cost of such asuspension bridge can easily be 20 to
30percent above the costs of a cable stayedbridge.
Currently, the second Nagoya Har-bour Bridge (in Japan), at 600
m (1967ft), has the longest span of a cable stayedbridge in steel.
This structure, which
54
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Fig. 3. Nagoya Harbour Bridge, Japan.
was designed by Dr. Ing_ KunioHoshino (a former student of the
au-thor), is now under construction. Whencompleted, it will look
similar to the firstNagoya Harbour Bridge (see Fig.3). Theauthor is
confident that in the near fu-ture similar such spans will be
builtusing prestressed concrete.
Range of span is only one importantparameter in designing cable
stayedbridges. Special situations such ascurved spans and skew
crossings can beeasily solved using stays.
The engineer can choose between alarge variety of
configurations: sym-metrical spans with two towers, un-symmetrical
spans suspended from onetower, or multi-spans with several towersin
between. This is an ideal field forcreativeness in design to
satisfy thefunctional requirements of the projectand to obtain an
aesthetically pleasingstructure which complements the
envir-onment.
2. The Main Girder System
2.1 Development of multi-stay cablesystem
Some of the first cable stayed bridges(like the Maracaibo
Bridge) had only
one cable at each tower (see Fig.4),leaving long spans requiring
a beamwith large bending capacity. Soon threeto five cables were
used, decreasing thebending moments of the beam and theindividual
cable forces to be anchored.However, structural detailing and
con-struction procedures were still difficult.
The desired simplification was ob-tained by spacing the cables
so closelythat single cables with single anchorheads were
sufficient which could eas-ily be placed and anchored. The
spacingbecame only 4 to 12 in (13 to 39 ft), al-lowing free
cantilever erection withoutauxiliary cables. Simultaneously,
thebending moments became very small, ifan extremely small depth of
the longi-tudinal edge beams and very stiff cableswere chosen.
This multi-stay cable system can nolonger be defined as a beam
girder.Rather, it is a large triangular truss withthe deck
structure acting as the com-pressive chord member. The depth ofthe
longitudinal beams in the deckstructure is almost independent of
themain span, but it must be stiff enough tolimit local
deformations under concen-trated live load and to prevent
bucklingdue to the large compressive forcescreated by the inclined
cables.
PCI JOURNALSeptember-October 1987 55
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Fig. 4. Development of structure to multi -stay cable bridge.
Note that additional cablesallow beam of superstructure to be
progressively more slender.
The stiffness of this new system de-pends mainly on the angle of
inclinationand on the stress level of the cables. Fig.5 shows the
enormous influence of thestress in such cables on the
effectivemodulus of elasticity. Low stresses givea large sag and
low stiffness. The stressin the cables should be at least 500 to600
N/mm2 (72500 to 87000 psi). Forlong spans, stiffening ropes (as
shown inFig. 6) are needed to prevent an exces-sive change of sag.
The simplification ofthe structural design and of the
erectionprocess gained by this multi-stay cablesystem should be
used whenever suit-able.
2.2 Arrangement of stay cablesIf all the cables are anchored at
the
top of the tower, the structural system iscalled a fan-shaped
configuration (seeFig.7). Unfortunately, the concentrationof the
anchorages causes structural diffi-culties when the number of
cables islarge. Therefore, it is preferable to dis-tribute the
anchorages over a certain
length of the tower head and get asemi-fan arrangement (as shown
inFig.8), which also improves the appear-ance of the bridge.
In the author's early bridges acrossthe Rhine River in
Dusseldorf, the ar-chitect wanted to have all the cablesparallel
and the anchorages equally dis-tributed over the height of the
tower.This is called the harp-shaped arrange-ment (see Fig. 9). The
system requiresmore steel for the cables, gives morecompression in
the deck and producesbending moments in the tower. How-ever, the
structure is aestheticallypleasing, especially when looking at
thebridge under a skew angle. Dr. UlrichFinsterwalder, the world
renownedbridge engineer, prefers this harp ar-rangement with many
closely spacedcables. Such a scheme was chosen forthe Dame Point
Bridge in Florida (seeFig.10), with a main span of 396 m (1298f3),
which is now under construction.
In these multi-stay bridges, the deckis hung up with cables near
the tower
56
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Y Z f2 E,EeffN1mm2
eff - o12 G3
205 000700
180 000 ^; SO 600
steel stressSao
140 000^p0
100 000oti
T
60 000sag
T{C
0100200300400 fc
Fig. 5. Effective modulus of elasticity depends primarily on
steel stress incable which in turn affects the cable sag.
Fig. 6. Stiffening ropes afixed to long cables reduce cable
sag.
PCI JOURNAL/September-October 1987 57
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Fig. 7. Fan shape arrangement of cables.
rFig. 8. Semi-fan arrangement of cables.
Fig. 9. Harp shape arrangement of cables.
also, to avoid a stiff bearing at the tower.This could cause
very large negativebending moments which might be un-acceptable for
the small depth of deckgirder used.
Normally, the bridge is supported bycables in two planes along
the edges ofthe deck. In some cases (mainly formedium spans),
cables in one plane areused along the centerline of the deck. Abox
girder with sufficient torsionalrigidity is then needed which
requiressome depth so that it can also resist thelarge bending
moments. Such a girdermust be supported at the tower to
resisttorsion and as a consequence the cablescan begin at a certain
distance from thetower, leaving a "window" in the cablenet open.
The Brotonne Bridge in
France is such an example (see Fig.11).Of course, other cable
configurations
are possible, depending on Iocal condi-tions, like very short
side spans. A har-monic arrangement of cables is impor-tant for
good appearance and it shouldbe chosen with care and diligence.
2.3 Ratio between main and sidespans
The ratio between side span l andmain span I has an important
influenceon the stress changes in the back staycables which holds
the tower back to theanchor pier. Live load in the main
spanincreases these stresses whereas liveload in the side span
decreases them.These stress changes must be kept
58
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"Jam 396m 192m
Fig. 10. Dame Point Bridge across St. John's River, Florida,
with centralexpansion joint; design by Ulrich Finsterwalder.
458.50_ 55.5DJ. 143 .5032C,DO I143, SO17D.o0 155.50 39
Fig. 11. Semi-fan arrangement of cables leaving a "window' open
near thetower; Brotonne Bridge, France.
safely below the fatigue strength of thecables. This fatigue
strength is a criter-ion for the allowable ratio 1,/1, which
de-pends mainly on the relation betweenIive and dead load, p
tog.
Prestressed concrete bridges allowlonger side spans than steel
bridges.The author has published charts in astate of the art report
for IABSE (1980)from which suitable ratios can he read.For concrete
highway bridges 1,ll can beabout 0.42; for railway bridges the
ratioshould not be larger than 0.34, The ratiodecreases with the
span length. Themagnitude of the anchorage forces at theanchor pier
also depends on the ratio1,/I. In particular, short side spans
givelarge anchorage lorces.
If there is no need for large free sidespans, then a rather
heavy continuousbeam bridge with spans of about 40 m(131 ft) can be
used as a long anchoragezone in which all cables act as back
stays
and concentrated vertical anchorageforces can be avoided (see
Fig. 12). Thissolution is especially advantageous if avery long
span is hung up to one tower.
If only a short or even no side span ispractical, then the back
stay cables canbe ground anchored over a certainlength or even be
joined in an anchorblock. This has been done for theC. F. Casados
Bridges in Spain, the Bar-rios de Luna Crossing (see Fig.13)which
at 440 m (1443 ft) is currently thelongest span of prestressed
concrete,and the Ebro Bridge (see Fig.14) whichhas an inclined
tower and back stay ca-bles spreading sidewise into two
planes,giving a most interesting impressionfrom the highway.
The inclination of the tower back-wards makes the main cables
longer, thebackstay cables shorter and steeper.There is no
technical or economical ad-vantage in this but a more thrilling
ap-
PCI JOURNAUSeptember-October 1987 59
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heavy beam bridge-alight stayed bridge
Fig. 12. Heavy beam bridge used as anchor zone for back stay
cables.
90,00
anchor anchor
joint in center_J+ 101.71 440,00 101,71Fig. 13. Back stay cables
anchored in ground; Barrios de Luna Bridge, Spain.
jjjj'.anchors on rock -
' 1371232,0025,50
146,30 57,6D
I ly, l 11 1 -I l l lIl l1411 IIIII I I f H I :IIINI ry I I H
d{I 6# -_ ^
y nl'^III'1.111lfl IIIIH1'IIIIII h+I H..
tower^cable5 In median 4m medianbackstay cables
Fig. 14. Back stay cables spread sidewards: Ebro Bridge,
Spain.
60
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fan shapeharp shape
4^ /hh 11
3ti
o^u`O 2
C ianQ
a 1 harpNgood
range
h/{
0,10,20,30,4
Fig. 15. Quantity of cable steel as a function of relativeheight
of towers.
pearance. A forward inclination of thetower towards the main
span producesuneasy and uncomfortable feelings.Towers should
normally be vertical.
3. Optimal Height, Shape andStiffness of the Towers
The cable forces and the requiredquantity of cable steel
decrease with theheight of the tower above the road level(see
Fig.15). A good range is between021 and 0.251. For bridges with
only onetower the height must be related to about1.81. Towers of
cable stayed bridgesmust be higher than those fbr suspensionbridges
which usually have h/I = 0.10.
The height of the tower also definesthe angle of inclination of
the longestcables. This angle should not be smallerthan about 25
degrees because other-wise the deflections will become
toolarge.
In the longitudinal direction the tow-
ers should be slender and have a smallbending stiffness, in
order to avoid largebending moments to he reacted by
thefoundations. If the soil conditions arepoor, then towers can
even he hinged atthe foot and fixed only during erection,The towers
of some of the author's RhineRiver bridges have such foot
hinges.Towers should be built of concrete be-cause concrete towers
are much cheaperthan steel towers.
The shape of the towers can be verysimple. Even for large spans
up to 500 m(1640 ft), free standing tower legs maybe sufficient if
they are fixed and trans-versely connected in the foundationonly i
see for example the Kniebriicke inDusseldorf (Fig.16) ] , No
transversebracing is needed if the cables are in avertical plane
and if the cross section ofthe tower is unsymmetrical with most
ofthe load carrying area close to the bridgedeck (see Fig.17). This
arrangementbrings the center of gravity close to the
PCI JOURNAL,+ September-October 1987 61
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""1
Fig. 16. The slender free standing towers of Kniebrucke in
Dusseldorf, West Germany.
section at top
cable - anchor-zone
cables
Sectionat deck
Fig. 17. Efficient cross section for freestanding towers.
plane of the cables and still gives muchtransverse bending
stiffness to carry thewind reactions to the foundation. Suchtower
legs should be tapered in both di-rections. Modern climbing forms
allowthis tapering without much extra cost.
The bridge deck with the railingsshould run clear through the
tower legsand the cable anchorages should beclose to the railings;
therefore, veryslender tower shafts become desirable.If the
semi-fan cable arrangement isused, then one or two transverse
brac-ings between the tower legs are suitable(see Fig.I8). The
bracing above the roadlevel should be slender and look lightbetween
the thin cables.
For very long spans and especially inregions with strong wind
forces, the A-shaped tower is the optimal solution forappearance
and wind stability (seeFig.19). In high level bridges, the
towerlegs can be joined under the deck levelin order to combine the
foundations.The Farb Bridge in Denmark was de-signed in such a way.
These A-shapedtowers with the cables sheltering thehighway give a
feeling of safety to themotorist and an exciting and pleasingview
(see Fig. 20).
62
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Fig. 18. Tower shapes for two planes of cables.
m-00_I high level bridge
tower sections
1V
River bridgelow level sea -high level
Fig. 19. A-shaped towers for two cable planes_
PCI JOURNAL/September-October 1987 63
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Fig. 20. View of A-shaped tower as motorist approaches bridge.
There isan inherent feeling of comfort and safety.
For bridges with cables in one plane itis best to design a
slender single towerin the median strip and to protect thecables
and the tower with strong guard-rails (see Fig. 21) as was done for
theRhine Bridge in Bonn, the BrotonneBridge in France, the Sunshine
SkywayBridge in Tampa, Florida and otherbridges. Tower shapes for
such bridgesare shown in Fig. 22.
4. Development of CrossSection of Deck Structures
The cross section which the authorselected in 1972 for the first
long span
cable stayed bridge using precast pre-stressed concrete, namely,
the Pasco-Kennewick Bridge (see Fig. 23) over theColumbia River in
Washington Statewas influenced by the wind tunnel testsconducted at
the NFL of Ottawa (1968).These tests were done to find the opti-mal
aerodynamic shape for the author'sdesign of the Burrard Inlet
Bridge inVancouver for a span length of 760 m(2492 ft).
The wind nose and the slight inclina-tion of the bottom face
gave the lowestwind coefficients and, therefore, thebest provision
for wind stability. How-ever, during the design of the Parana
f
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Fig. 21. Tower in median of Rhine Bridge in Bonn-Nord,West
Germany.
Bridges in Argentina for highway plusrailway traffic, it was
conceived that thisaerodynamic shape was useless when400 m (1311
ft) long freight trainswere on the bridge. Through dynamictests it
was learned that multi-stay cablebridges have very strong damping
coefficients and do not need the same goodaerodynamic shape as
suspensionbridges do. Therefore, the cross sectioncould be
simplified further.
The following can be concluded:For spans up to about 150 in (492
ft)
and for widths up to about 20 m (66 ft), avery simple solid
concrete slab withoutan edge beam is the best solution (see
Fig. 24). The thickness of the slab de-pends primarily on the
transversebending moments which can be in-creased towards the
towers to respond tothe increasing longitudinal normalforces.
Dr. Finsterwalder had proposed suchslender slabs as early as
1967 for his de-sign of the Great Belt Bridge and lateralso for the
Pasco-Kennewick Bridge.The thickness of the slab was so small
inrelation to the span that the safetyagainst buckling under high
longitudi-nal compressive forces was subse-quently questioned
especially in thecase of high deflections under concen-
PCI JOURNAL/September-October 1987 65
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Fig. 22. Tower shapes for one plane of cables.
4coble%
22.50 m
Fig. 23. Cross section of Pasco-Kennewick Bridge (1972),
Washington State.
50 -60cm
15 20 m
Fig. 24. Cross section with solid slab only for highway bridges
with spans up to 150 m(490 ft).
66
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Fig. 25. Bridge across the Rhine at Diepoldsau, West Germany.
Span = 97 m (318 ft).
trated live load and the possibility thatone cable could break
in an accident.
This buckling safety was meanwhilestudied by Professor Renee
Walther inLausanne, Switzerland. Second ordertheory calculations
were checked bytests with a relatively large model.Buckling safety
could now be checkedreliably. It was found that a certainamount of
longitudinal reinforcement isrequired for obtaining sufficient
ductil-ity in such thin slabs.
Professor Walther became the firstengineer to build a highway
bridge 15 m(49 ft) wide across the upper RhineRiver in Diepoldsau
with a slab only 50cin (20 in.) thick for a main span of 97 m(318
ft) with no edge beams (see Fig.25). He even reduced the slab
thicknessat the edges to 36 cm (14 in.).
For wider bridges, B>2() ni (66 $),transverse T beams are, of
course, moreeconomical (see Fig. 26). The spacing ofthe beams
should not be Iarger than 4 to
25-30m
t,y
1+- 4=6m^
Fig. 26. Cross section with transverse beams for width greater
than 20 m (66 ft) andspans up to 500 m (1640 ft).
PCI JOURNALiSeptember-October 1987 67
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27, 53-
1,3712,160,4512,161,37
prefab. stab 280rnm+50mm special layer
8 0.4'2%2%O.CB
2.33r 1.75 L165A
Steel cross girder @3,8m
28,Q m
Fig. 27. Cross section of Sunshine Skyway Bridge, Florida,
showing composite structure(not built).
6 m (13 to 20 ft) and the slab on topshould always span
longitudinally tomake good use of the longitudinal com-pressive
forces from the cables. Thecross beams can he cast in place or
pre-fabricated and end in a thick edge beamwith a depth of not more
than 1.0 to 1.5m (3.2 to 4.9 ft), giving ample bucklingsafety and
keeping the curvature of thedeflection line under concentrated
loadswithin allowable limits even for spansup to 5{l0 m (1640
ft).
Such cross sections are especiallysuitable for composite
structures, usingsteel cross girders between concreteedge beams
which the author designedfor the East Huntington Bridge. Its 274m
(898 ft) span hung up to one towercorresponds to a span of about
500 m(1639 ft) if suspended from two towers.In the proposed design
(conducted bythe author's consulting firm) of the Sun-shine Skyway
Bridge (see Fig. 27) in1980, a 2 m (6.6 ft) deep steel edge beamwas
used to simplify the erection pro-cess and to allow the use of
prefabri-cated deck slabs.
Soon thereafter, this type of sectionwas chosen for the Annacis
Bridge inCanada with a main span of 465 m (1525ft) together with
some advanced details.The project was built in 26 monthswhich is
remarkable considering the
structure is 1000 m (3286 ft) long. Thisefficiency shows the
ease and simplicityof the erection method.
In these composite structures, theconcrete must remain the main
struc-tural material. The deck slab has to carrythe compressive
chord forces. If for verylong spans these thrust forces becometoo
large for the normal deck slab, thenits thickness should be
increased to-wards the tower or a concrete edgebeam should be
added. However, thesteel section should remain small inorder to
avoid creep problems.
If the bridge is hung up with cables inthe median only, then a
box girder isneeded. The cross section of the Bro-tonne Bridge (see
Fig. 28) has become astandard for this type. The requiredamount of
torsional rigidity depends onthe width of the deck and the length
ofthe main span. Smaller cross-sectionalareas of the box may often
be sufficientand this would allow sections like thatshown in Fig.
29, which is simpler toconstruct and has a smaller depth andsimple
cable anchorages.
For railroad bridges, especially forhigh speed trains, large
mass is neededto get a good dynamic behavior. There-fore, the DB
German Federal Rail-ways carry the 40 cm (15 in.) deepballast over
their modem bridges and
68
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i,506,50 ^1^05.501,50
5,60 -- 4.00 --- 4,00 5.60 --
Fig. 28. Cross section of Brotonne Bridge, France, showing
cables in the median.
prefer thick concrete deck slabs. Withhigh strength cables it is
not difficultand also not too costly to carry suchheavy dead loads
over long spans (seeFig. 30).
Edge beams 1.5 to 2.0 m (4.9 toi.6 ft) deep should he sufficient
to
satisfy deflection limits if the cables arenot too flat. For
very long spans and se-vere deformation limits, a flat box sec-tion
may be needed (see Fig. 31). Thecables of such railroad bridges
shouldhave angles of inclination above 30 de-grees.
Fig. 29. Slender cross section for cables in the median with
simple anchorage (BrotonneBridge, France).
PCI JCURNALJSeptember-Oclober 1987 69
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14,00
Fig. 30. Cross section of railroad bridges for spans up to 140 m
(459 ft).
Fig. 31. Cross section of railroad bridges with spans longer
than 140 m (459 ft).
liveload______________iiii11111111 II liiiLI..L.i._II1.1I
111111111111
L 0,4510.45Fig. 32. Deflection line showing large angular
changes at the endsof side spans.
70
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Fig. 33. Continuity to a short approach span avoids largeangular
changes.
5. Situation at the Ends ofCable Stayed Bridges
The sudden change from an elasticsupport to a stiff support at
the ends ofthe side spans causes large bendingmoments and
consequently a large an-gular change of the deflection line
(seeFig. 32). These angular changes are un-acceptable for railroad
bridges.
The difficulties can easily be avoidedif the edge beams continue
with an in-creasing depth into a small approachspan (see Fig. 33).
The length and thebending stiffness of this smootheningtransition
span must be well designed toavoid large bending moments.
This transition span can also be usedto counteract the uplift
forces of the backstay cables by its weight or even by bal-last
concrete within its depth. It also al-lows the distribution of the
anchoragesfor the back stays over a certain lengthbehind the axis
of the anchor pier.
6. Cables and TheirAnchorages
6.1 Cables and Their ProtectionThe cables are the most
important
members of this system. They must besafe against fatigue,
durable and wellprotected against corrosion especially
in an aggressive environment. The besttype of cable must be
chosen and not thecheapest. It is unwise to save a few per-cent of
steel and to later have to replaceropes with broken or corroded
wiresafter only 8 to 12 years as was the case inthe Knhlbrand and
Maracaibo Bridges.
Regarding the choice of cables, testresults and practical
experience of morethan 30 years are available. The follow-ing is
the author's opinion based on ex-perience and judgment.
There is no doubt that bundles ofparallel wires or parallel long
lay strandsdeserve preference due to their highand constant modulus
of elasticity. Thequality of the wires or strands must bewell
controlled because very differentqualities are on the market. Wires
with adiameter of 7 mm of St 1470/1670 N/mm2are generally used, the
number of wiresper cable can be 337, giving a maximumultimate force
of Pq = 21.7 MN or 2170tons. Applying the rather high factor
ofsafety of 22, the allowable cable force isabout P = 10.0 MN or
1000 tons. Itwould be better to choose a lower safetyfactor, Le.,
1.7, but instead refer it to the0.2 percent yield strength.
Strands are available of St 1500/1700Nlmm2 with a diameter of
12.7, 15.7 and17.8 mm (0.5, 0.6 and 0.7 in.). The big-gest bundles
have 91 strands, yielding toP = 31.4 MN or 14 MN allowable
force.
The wires or strands are closely
PCI JOURNAUSeptember-October 1987 71
-
rig, s4. Section through cable with strands.
packed together to minimize the diam-eter for the protecting
pipe (see Fig. 34).These cables should only be used forwide and
heavy bridges; normallysmaller cables lead to a reasonablespacing
and can he easier handled.
With regard to the high stress changesof back stay cables,
special anchorageshave been developed which avoid thedamaging
effect of hot metal filling insockets which is generally used for
ropeanchors.
The Swiss firm BBR developed theHIAM (high amplitude) anchorage
(seeFig. 35) using their button heads at theends of the wires or
strands to set a coldsteel ball filling tinder transverse pres-
DEAD ENDCircular shim-- Locking plateWires
Button headPE:"pipe ,LIVE END-- Steel pipe
Fig. 35. HIAM anchorage of BBR.
Anchor headNutBearing plate
Neoprene damper
FTension ringConnection pipe
Stay tube
Grout capL7ransition pipe
Fig. 36. VSL anchorage for strands.
72
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Fig. 37. Cables in polyethylene pipe on reels for transport.
sure inside the cone of the socket.Hereby, stress amplitudes of
o- = 300Nlmm2 (43500 psi) can be resisted withover 2 million cycles
(according to thelatest Swiss publications). Japanesetests
confirmed these favorable values ofthe HIAM anchorage.
Since the number of wires in one an-chorage has influence,
special testingmachines had to be developed to testthese big
bundles at full size with pul-sating forces up to 700 t (772 tons).
TheSwiss firm VSL has developed an an-chorage (see Fig. 36) holding
up to 91strands with wedges, yielding a fatigueamplitude of Av =
200 N/mm2 (290000psi). The Freyssinet group and Dywidaghave
anchorages for strands with similarqualities.
For corrosion protection, a polyethyl-ene (PE) pipe around the
wire bundle isthe optimal solution. The PE is maderesistant against
ultraviolet rays byadding 2.5 percent of carbon black.
More than 40 years of experience hasshown that this material is
durable intropical regions as well as in polluted airof an
industrial environment. The fewcases in which PE pipes were
damagedby cracking have been traced to causeswhich can safely be
avoided. Of course,quality control, sound judgment or theretention
of a consultant are necessary.
The PE pipe can be pulled over thebundle or applied by
extrusion. Itshould be at least 7 mm (0.275 in.) thick.PE is
impermeable to vapor and givesfull corrosion protection. Therefore,
thematerial to fill the voids inside the pipein order to take
moisture and oxygenout, must not have anti-corrosive qual-ities.
Usually, cement grout is injectedafter the cable is under dead
Ioadstresses because cement grout is thecheapest filling material
and also hasgood corrosion protection characteris-tics. However,
this injection procedureis not always liked on the site. In the
PCI JOURNAL/September-October 1987 73
-
Cable in PE pipeRubber sleeve
Thick steel pipe
Height forprotection/Neoprene pad
(damperl
HIAM Anchor, fixed, adjustment in tower
Fig. 38. Standard cable anchorage at the deck.
future, the cables will most likely befilled in the factory with
a rubberlikedeformable material.
The PE pipe must be tightly and reli-ably fixed to the anchor
socket so thatthe cable can be finished in the factory,
Fig. 39. Crossing of cable anchorages intower head.
rolled on reels (see Fig. 37) for shipping,and easily handled at
the bridge site.These advantages cannot be obtainedwith steel pipes
around the bundlewhich must in addition get painted
forprotection.
The only disadvantage of the PE pipeis its black color, which
detracts fromthe good appearance of the bridge in itsenvironment.
Therefore, the cables ofsome bridges have been wrapped with atape
ofa brighter color like ivory or winered. The tapes of PVC used at
thePasco-Kennewick Bridge deterioratedafter about 6 years. Later,
Tedlar tapesof polyvinyl fluoride were used forwhich a 20 year life
is expected. Thiswrapping does not cost much but it em=bellishes
the bridge as can be seen fromthe color photos of the East
HuntingtonBridges
6.2 AnchoragesThe anchorages must be designed to
allow adjustment of length and replac-ing a cable damaged by an
accidentwithout interrupting the traffic. They mustfurther be
designed to prevent bendingstresses in the wires or strands at
thesocket due to change of sag or due toslight oscillations. The
anchorage
74
-
easyaccess
main side span
neoprene pad
sleeve\ __-
steel pipe
crosssection
prestress - bars orloops
Fig. 40. Cable anchorage inside tower with box section.
should further comprise dampers toprevent resonance oscillations
of the ca-bles caused by wind eddies (followingthe von Karman
effect).
The anchorage at the deck structurewhich the author designed for
thePasco-Kennewick Bridge in 1972 hasmeanwhile become the accepted
solu-tion (see Fig. 38). A strong steel pipe isencased in the
concrete with the correctangle of inclination. The diameter islarge
enough to thread the anchor socketof the cable through the pipe and
placeshims or turn the anchor nut on, which
allows length adjustment. The steelpipe extends about 1.2 m (3.9
ff) abovethe road level to protect the cableagainst aberrant
vehicles. On its topthere is a thick soft neoprene pad, whichacts
as a damper and stops flexuralmovements of the cable. The top
issealed with a rubber sleeve.
At the tower head, cables runningover a saddle like in a
suspension bridgeshould be avoided because their re-placement would
be rather difficult. It ispreferable to anchor the cable at
eachside individually and to design devices
PCI JOURNAL September-October 1987 75
-
il`IIA_____ iII^ IIYVII
I.
Fig. 41. Cable anchorage by means of a steel beam insideconcrete
tower.
to carry the horizontal component of thecable forces through the
tower. Thesimplest solution is shown in Fig. 39 inwhich the cables
cross each other, againin steel pipes. This is easy if there
aresingle cables towards the main span andtwin cables for the short
side span.
Since the concrete towers usuallyhave shafts with a box section,
it is prac-tical to arrange the anchorages insidethis box section
as shown in Fig. 40. Thehorizontal component of the cables istaken
up in the longitudinal box wallsby prestressed bars. All anchorages
areeasily accessible. There must be suffi-cient space for applying
a jack to adjustthe cable length, which can be donehere much easier
than at the deck an-chorages. At the end of the steel pipethere is
again the neoprene pad and thesleeve.
For the Annacis Bridge, the pre-stressing was avoided by placing
short
steel beams inside the box sectionwhich take the horizontal
component ofthe cable forces (see Fig. 41). Thesebeams must be well
anchored for unbal-anced horizontal forces during erectionor for
the case in which a cable must beexchanged. The tower box must be
wideenough to allow access and handling ofthe jacks. All these
solutions make theerection very simple if prefabricatedflexible
cables with slender anchorsockets are used.
7. Dynamic Behavior andAerodynamic Stability
The cable stayed bridges with con-crete decks and highly
stressed cables[Efn > 180000 N/mm2 (26,100,000 psi)]have a very
favorable dynamic behavior.The deflections under live load are
ex-tremely small because the effectivedepth of the large cantilever
truss
76
-
^AL4Sd6^iY.d4C^.H.VA'.6'.O
.^QiASO'.6^iQ60^i8^i6^^6fiY.4G6'r62G5y^6'G^ ^l4L9q
- t
B a 10 H
H
B 10 H+i
Fig. 42. Geometrical relations for obtaining wind stability
withcables at beam edges.
formed by the cables is much larger thanfor beam girders.
Most important is the fact that the in-crease of amplitudes due
to resonanceoscillation is prevented by systemdamping caused by the
interference ofthe many cables. This is an advantage ofthe
multi-cable system. Measurementsat the Tjbrn Bridge in Sweden
showedthat the damping increases with in-creasing amplitudes and
the logarithmicdecrement gets well above 0.10.
This damping is very favorable for thewind stability. Current
theories whichcalculate critical wind speeds do notadequately
represent the actual be-havior and have only limited validity.The
same is true for wind tunnel testswith sectional models in which
only aconstant damping factor is applied.More tests should be made
of actualbridges to improve our theories basedon observed
facts.
From our present knowledge we cansay that there is no danger by
wind withconcrete bridges hung up with cables in
two planes along the edges, if the fol-lowing geometrical
relations are ob-served (see Fig. 42);
1.B >10H2. For B < 10 H, a wind nose should
be added.3. B -- 1130 L. This means that the
width of the bridge should not betoo small in relation to the
mainspan. If this ratio gets smaller, thenA-shaped towers and wind
shapingof the cross section must be used.
The A-shaped tower gives a triangularshape of the cable planes
and the deck,which increases the torsional rigidity.
The author was a consultant in the de-sign of the bridge at
Posadas Encar-nacion, Argentina (see Fig. 43), whichhas to be safe
against tornados with theirenormous uplift forces. A rather
heavybox girder and A-shaped towers wereselected to get the
required safety.H. Cabjolsky reported on this bridge atthe FIP
Congress (1986) in New Delhi.
Bridges hung up with cables in oneplane along the center line
have almost
PCI JOURNAL'September-October 1987 77
-
Fig. 43. Erection of Posadas Encarnacibn Bridge, Argentina.
no damping for torsional oscillations.Caution is recommended
because thiscase has not been sufficiently studied.
Caution must also be taken for someerection stages mainly during
free can-tilevering on both sides of the towersespecially if the
cantilever length be-comes larger than 20 B. Unsymmetricaland
inclined wind forces can causetrouble. Temporary wind noses or
ropesto submerged anchor blocks can preventdangerous
oscillations.
8. Prestressing ofCable Stayed Bridges
For bridges with cables along bothedges longitudinal
prestressing of thedeck structure is needed only over acertain
length in the middle of the mainspan, if towers stand on both
sides. Thehorizontal thrust forces of the cables arezero in 1/2;
there may even be tensiondue to restraint forces caused by
bear-ings and unsymmetrical live load. Fur-ther, there are bending
moments due to
concentrated live load. In slabs asshown in Fig. 24, the
longitudinal ten-dons can be distributed over the widthof the
bridge with some concentrationnear the edges. In cross sections
likeFig. 26, all tendons can be placed in theedge beams.
The longitudinal thrust in the deckdue to the cable forces
increases to-wards the towers, causing so much com-pression that no
additional prestressingis needed there. However, towards theends of
the side spans, this thrust de-creases and the bending moments
in-crease; consequently, longitudinal pre-stressing is needed.
Since the bendingmoments are mainly caused by local liveload with
maxima conditions rarelyhappening, partial prestressing will
besufficient.
Transverse prestressing is desirablefor widths between 10 to 15
m (33 to 49ft) mainly at the ends of the side spans,where the
spreading out of the cableforces over the width of the deck
causestransverse tension. For wider bridges,transverse prestressing
should generally
78
-
be used against transverse bending andtransverse normal forces
caused by thecable forces. The degree of prestressingnay be chosen
for no tension in the con-crete due to dead load plus 20 to 40
per-cent live load depending upon theweights of national live load
specifica-tions which vary considerably through-out the world.
For bridges hung up by one row ofcables along the centerline
with a boxgirder, more longitudinal prestressing isneeded, because
the large bendingstiffness of these girders cause large pos-itive
and negative bending moments.The tendons may be placed in the
topand bottom slabs. Transverse pre-stressing is needed for the
transversebending moments and to counteract tor-sional stresses
which can be rather largetowards the towers. A high degree
ofprestressing is suggested here, becausethe torsional rigidity
gets almost lost, assoon as cracks due to tensile stressesoccur
(see Chapter 7 in Ref 4).
If segmental construction with prefab-ricated elements is chosen
with no lon-gitudinal reinforcement across thejoints, then a rather
high degree of pre-stressing is imperative in the longitudi-nal
direction. This prestressing preventspartial opening of these
joints due todifferential shrinkage and creep whichis caused by
frequent high temperatureof the deck slab (sunshine) and often bya
different thickness of the members(web thicker than bottom slab,
etc.). Thehigh degree of prestressing is especiallyneeded if
unbonded external tendonsare used and no reinforcement crossesthe
joints, in order to get the requiredsafety for the ultimate limit
state.
9. Construction MethodsThe common construction method for
multi-stay cable bridges is free canti-levering from the tower
towards bothsides.
The final cables are used to supportone segment after the other.
Since full
symmetry of loadings can usually not besecured, the tower must
be stiffenedunder the deck by struts or by retainingcables from the
tower head to suitableanchor points.
For cross sections like those shown inFigs. 24 and 36, casting
the segments inplace is preferred because the joints canbe secured
by overlapping longitudinalreinforcement which helps to
preventcracks due to unforeseen restraintforces. Such reinforcement
also aids insecuring the required safety for the ul-timate load
condition, A part of the edgeor edge beam with the anchor steel
pipein the correct position can be prefabri-cated and fixed to the
cantilevering steelgirder carrying the forms. The construc-tion
head can be sheltered against theweather.
For bridges with box girders, prefab-ricated segments can be
used withmatch cast joints but using a paste in thejoint which
compensates for differentialshortening during the curing and
hard-ening period. Prefabricated segmentscan also be mounted,
leaving a gap Foroverlapping longitudinal reinforcementby means of
steel hinges on the webs,which allow adjustment for the
correctpositioning of the segment. This hasbeen done successfully
at the ParanaBridge in Posadas EncarnaciOn (see Fig.43).
Bridges with a deck of compositebeams allow the simplest and
quickesterection. The grid of steel cross girdersand light steel
edge girders, includingthe cable anchors, are installed with
lightderricks and then the prefabricated con-crete slabs are
placed, leaving gaps foroverlapping reinforcement and
shearconnectors which are closed by cast-in-place concrete. The
Annacis Bridge inVancouver, British Columbia, is a goodexample.
The cables in PE pipes have recentlybeen pulled up to the towers
from thereels standing on the deck or even fromboats without any
auxiliary cables usingonl y curved saddles with rollers in
order
PCI JOURNAUJSeptember-October 1987 79
-
to prevent excessive bending. Thehauling equipment must be
strongenough to pull the cable socket into thedeck anchor. The last
stretch is done bya hydraulic jack which can resist the fulldead
load cable force.
During the last ten years, constructionmethods have shown major
progress to-wards simplification and reducing erec-tion equipment,
The construction must,however, be well planned using step bystep
calculations for the alignment,forces, exact lengths and angles
consid-ering temperature and creep influences,which depend on
seasonal, climatic andeven daily conditions. The old rule mustbe
observed that all measurementsshould be made early in the
morningbefore the sun rises. Special expertise isstill needed,
which is rather rare, sincemost universities do not teach such
es-sentials for practical work.
10. Closing RemarksDue to limited space, the author had
to omit several subjects which are im-portant for a modern
design of a cablestayed bridge. For example, in multi-span bridges,
the best arrangement ofbearings and joints or provisions
againstseismic damage are not covered. Also,codes of practice and
project specifica-tions, which often are not up to datewith respect
to the latest research andexperience, are not mentioned.
Nevertheless, the author hopes thathe has demonstrated how
simple thecross sections and the details of thesebridges can be if
our collective experi-ence and knowledge gained during thepast
thirty years is well exploited. Theauthor is confident that such
cablestayed bridges of prestressed concretewill have a wide field
of application inthe future in countries throughout theworld to
serve the needs of human soci-ety.
But in our work, let us always searchfor good quality,
durability, ease of in-spection and maintenance and espe-cially let
us not forget the aesthetics of astructure as it affects the
environment.
REFERENCES1. Leonhardt, F., and Zellner, W., "Verg-
leiche zwischen Hange- andSchragkabelbrucken fur SpannweitenCher
600 m, " Band 32 der IVBH-Abhandlugen, Zurich, 1972.
2. Leonhardt, F., and Zellner, W., "CableStayed Bridges," IABSE
Surveys, S 13/80,Zurich, 1980.
3. Saul, H., Svensson, H., Andra H. P., andSelchow, H. J., "Die
Sunshine SkywayBriicke in Florida, USA," Bautechnik,Hefte 7 9,
Berlin, 1984.
4, Leonhardt, F., Vorlesungen Ober Mastic-ban, Teil 4, Springer
Verlag, Berlin, 1984.
5. Grant, A., "Design and Construction of theEast Huntington
Bridge," PCI JOURNAL,V. 32, No. 1, January-February, 1987,
pp.20-29.
80
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Toughness of Glass FiberReinforced Concrete Panels
Subjected toAccelerated Aging
Surendra P. ShahProfessor of Civil Engineering
and DirectorCenter for Concrete and
GeomaterialsNorthwestern UniversityEvanston, Illinois
James I. DanielSenior Structural EngineerConstruction
Technology
Laboratories, Inc.Skokie, Illinois
UtDarmawan LudirdjaGraduate StudentDepartment of Civil
EngineeringNorthwestern UniversityEvanston, Illinois
G lass fiber reinforced concrete(GFRC) is a cement based
com-posite product which is reinforced withglass fibers. GFRC
cladding panels areincreasingly being used in the UnitedStates and
other countries. These panelsare generally produced by
simultane-ously spraying a portland cement mortarslurry and alkali
resistant (AR) choppedglass fibers onto molds. The size ofproperly
designed panels with appro-priate configuration can he as large as
8x 30 ft (2.4 x 9.1 m) with only Vz in, (1.27cm) skin thicknesses.
GFRC panels are
relatively light in weight facilitatingtheir handling,
transporting and erec-tion. GFRC cladding panels are pro-duced as
wall units, window units,spandrels, mullions, and column covers.In
1985,