OUTSTANDING ENGINEERING ACHIEVEMENTS
PRESTRESSED CONCRETE IN CANADA
A Short History - 1952 to 2000
John R. Fowler
Canadian Precast/Prestressed Concrete Institute,
Ottawa, Canada
- Introduction
- Bridges
- Buildings
- Stadiums and Arenas
- Building Systems
- Other Structures
- Design Code
- Conclusion
This short history looks at how prestressed concrete came into use in 1952 in
Canada. Some innovative early applications of prestressed concrete are examined.
Research and more accurate design methods helped engineers to better understand
the behavior and performance of prestressed concrete. Prestressing materials
and technology developed rapidly worldwide. Outstanding bridges, buildings and
building systems, stadiums, arenas and other structures that have been constructed
between 1952 and 2000 are described.
The construction of the Walnut Lane Bridge was a most significant event and
is mentioned here even though it was built in the United States. It was the
dramatic groundbreaking project that showed North American engineers the practical
value of combining the compressive strength of concrete with high tensile strength
prestressing steel. The design of the bridge was based on European prestressing
technology and design methods introduced to North America after the Second World
War. Professor Gustave Magnel (1885-1955) of Belgium gave lectures to engineers
in the US and Canada in the mid 1940's to the early 1950's. Magnel's book "Prestressed
Concrete" attracted considerable interest in North America of the potential
for prestressed concrete.
Walnut Lane Bridge - 1949
Philadelphia, PA
The successful completion of the first bridge structure in the US with its
impressive 160-ft main-span and 74-ft end span precast prestressed concrete
girders inspired many engineers on both sides of the border to closely examine
the properties, benefits and design methods of prestressed concrete. Over 300
engineers from 17 states and 5 countries witnessed the formal testing to destruction
of an identical girder used in the main span of the bridge.
Owner Representative: Pennsylvania Bureau of Engineering, Surveys & Zoning
Designer: Preload Corporation
Contractor: Corbetta Construction Company & Raymond Concrete Pile Inc
Mosquito Creek Bridge - 1952
North Vancouver, BC
The Mosquito Creek Bridge in Vancouver has the distinction of being the first
prestressed concrete bridge built in Canada. This bridge proved to be both economical
and satisfactory from a structural viewpoint. The bridge is still in service,
having been widened on both sides over the years.
Engineer: Prestressed Concrete Engineering
Ross Creek Bridge - 1954
Medicine Hat, AB
This 60-ft span quickly bridge quickly followed the Mosquito Creek Bridge.
It is the first segmental precast concrete bridge in Canada and the first prestressed
concrete bridge in Alberta. Ross Creek Bridge has a span of 60 ft (18.3 m) and
a 25 ft (7.3 m) roadway. The deck consists of 10 side by side precast T-girders
with a depth of about 39 in (1000 mm). The equipment in 1953 did not allow for
safe transportation of 60 ft long girders. Therefore, the girders were precast
in three 20 ft (6.1 m) segments and shipped to the site where they were erected
on two temporary timber bents. After concreteing the 4 inch (100 mm) gap between
the ends of the segments at the splice, the girders were longitudinally post-tensioned.
The bridge was also laterally post-tensioned through the girder top flanges
and the diaphragms. It was subsequently determined that full size girders could
have been plant-cast, prestressed and trucked to the site.
Milestones: The bridge was designed in 1953. The girders were erected in January
1954. The bridge was completed in March 1954 and is still in service.
Owner: City of Medicine Hat
Designer: Structural Engineering Services of Calgary (now Lamb McManus Associates)
Precast Contractor: Con-Force
The success and lessons learned from this bridge and subsequent projects lead
to the development of standard factory cast bridge girders. The practice of
post-tensioning in the plant using high-strength wires gave way to pretensioning
with seven-wire strands and deflecting some strands in the forms. Supplemental
post-tensioning came to be used whenever extra prestress force or continuity
was required. Standard I-girders, box girders, channel slabs, solid and voided
slabs and bulb-tee girders were developed and increasingly used across Canada
by individual provinces, municipalities, the federal government and the railways
as the benefits of economy, durability and faster constructions were realized.
This process continues with larger, more efficient sections being developed
and placed in service.
Champlain Bridge - 1959-1962
Montreal, QC
At the time, this was the largest application of prestressed concrete in Canada.
Designed in concrete and steel, the precast concrete option used 53.6 m (176
ft) long precast pretensioned girders supported on T-shaped piers for 46 spans
across the St. Lawrence River and the Seaway at Montreal. The prestressed concrete
design came in 17% below the steel alternate.
Owner: National Harbours Board
Design & Construction Joint Venture: McNamara (Quebec) Ltd., Key Construction
Inc., Deschamps et Bélanger Ltée.
Design: Wardycha & Skotecky, Enterprise Fougolle, STUP
Design Review: H. H. Pratley
Kinnaird Bridge - 1964
Over the Columbia River, BC
This spectacular 5-span, 408 m long bridge's roadway is 55 m above the fast
flowing Columbia River. 15 special 45.8 m (150 ft) drop-in precast prestressed
concrete girders span between the triangular pier shafts and abutments. The
girders, each weighing over 100 t, vary in depth from 1.8 m at the supports
to 2.7 m at mid-span. They were post-tensioned in 3 stages during construction.
A launching truss was used to install the girders in sets of 3 @ 4.4 m c/c for
the 5 spans. Precast prestressed concrete hexagonal piles support the piers.
Precast diaphragm elements were used in the cast-in-place bridge piers.
Owner: BC Department of Highways
Engineer: Choukolos, Woodburn and McKenzie Ltd. with assistance from Professor
Morandi
Contractor: Northern Construction Co. and J. W. Stewart Ltd.
Bensfort Bridge - 1969
Peterborough, ON
The bridge is 34 ft (10.4 m) wide. 5 lines of standard 54 in (1.37 m) deep
CPCI IV girders 75 ft (24.4 m) long were spliced with 67 ft (20.4 m) haunched
pier segments to achieve the two 150 ft (42.7 m) main spans and the two 110
ft (33.5 m) end spans. The girders were erected on timber falsework with a double
key cast-in-place joint. The bridge was continuously post-tensioned over all
5 spans. This bridge design was very significant: precast girders capable of
spanning only 120 ft (36.6 m) in one piece were spliced in segments to achieve
much longer spans.
Owner: United Counties of Northumberland and Durham/County of Peterborough
Engineer: Totten Sims Hubicki & Associates
Precast: Wilson Concrete Products (now Pre-Con Inc.)
Post-tensioning: Conenco Canada
Refinement of the techniques used in the construction of the Bensford Bridge
lead to the construction of many other spliced-girder bridges across Canada,
including the Perley Bridge (1998) over the Ottawa River, Hawksbury, ON, with
main spans of 68.5 m.
Bear River Bridge - 1972
Digby, NS
This bridge was the first precast segmental box-girder bridge in North America
to be built using the short-line match-casting method. The curved bridge is
609 m (1998 ft) long with 6 interior spans of 80.8 m (265 ft) and 2 end spans
of 62.1 m (204 ft) Alternate bids were $3.36 million for the segmental precast
option and $3.6 million for a steel bridge. 145 single-cell box girder sections,
typically 11.4 m wide and 3.6 m deep, were required. Typical sections were 4.3
m long and weighed 82 tonnes.
Owner: Government of Nova Scotia
Design: A. D. Margison
Consultants: Bouvy, v.d. Vlugt & v.d. Niet
Post-tensioning: Potenco Inc.
Contractor: Beaver Marine Ltd.
Vancouver ALRT - 1982-1986
Vancouver, BC
The aerial guideway is a 16-km (10 mile) long ribbon of precast prestressed
concrete that follows the curvature of the track profile. The guideway has long
spans, in-depth crossheads and a minimal visual impact on the urban areas through
which it passes. This project was the largest precast contract ever awarded
- and one of the most complex precast projects ever built in Canada at the time.
Beam production cost $54 million, the total guideway cost $249 million and the
total project cost was $802 million. Typical spans up to 45 m used single precast
trapezoidal girders in each direction, as a series of two-span continuous structures,
that rested on graceful T-shaped column piers. For Phase II, 1040 (484 tangent,
556 curved) girders were manufactured between April 1983 and October 1984. Girders
were cast in two stages: first the bottom flange and webs with the prestressing
and shear reinforcing. The following day the interior forms were removed and
the reinforced top flange was cast. A jig containing threaded inserts was used
to accurately position the track fastenings in the girders. A complex adjustable
articulated form was used to cast the curved and superelevated girders. The
prestressed straight and curved box girders were found to be the most economical
solution for the aerial guideway.
Owner: BC Transit
System Contractor: Metro Canada Ltd.
Guideway Designer: ABAM Engineers Inc.
Prebuild Precast: Con-Force Structures Ltd.
Phase II Precast: Supercrete, A Division of Canada Cement Lafarge Ltd.
Prebuild Erector: Commonwealth Construction Ltd.
Phase II Erector: Peter Keiwit Sons Co. Ltd.
Confederation Bridge - 1993-1997
Cape Tormentine, NB, to Borden, PEI
No accounting of the accomplishments in prestressed concrete in the 20th century
would be complete without including the Confederation Bridge, a two-lane fixed-link
12.9 km (8 mile) bridge. The main bridge has 44 - 250 m spans that rise up to
a navigation channel in the middle of the structure. This part of the bridge
used 175 precast concrete components (hardpoint segments, pier bases and shafts,
main and drop-in girders). The bridge used the latest in high performance concrete
technology and is designed to achieve a 100-year service life. The bridge was
built in record time using massive precast concrete segments, the largest being
the 160 m long pier sections that weigh 7500 tonnes. Components were moved about
the casting yards using 8000-tonne capacity Huisman sleds and installed by the
Svanen, a specially designed floating catamaran crane. The shallow water approaches
were built using tapering box girder segments erected using the balanced cantilever
method.
Developer: Strait Crossing Development Inc.
Contractor: Strait Crossing Joint Venture
Independent Engineer: Buckland & Taylor Inc.
Engineer of Record: J. Muller International
Design Engineer: JMS Joint Venture - Partners - J. Muller and SLG/Stanley
Grosvenor House - 1960
Winnipeg, MB
This apartment building was originally designed as cast-in-place concrete.
The City of Winnipeg was just accepting prestressed concrete at the time of
construction. An alternate design was prepared in precast with assistance from
Lawrence Cazaly. When completed, this 8-storey apartment building was the tallest
all-precast building in Canada. Over the years, acceptance of precast prestressed
concrete is higher per capita in Winnipeg than anywhere in Canada.
Precast Contractor: Building Products & Coal Ltd., later PRECO, now Con-Force
Bromley Place
Calgary, AB
This
31-storey apartment building is the tallest totally precast concrete building
in Canada.
Owner & Contractor: MBS Construction (1977) Ltd.
Architect: IKOY Architects
Consulting Engineers: J. R. Spronken & Associates / W. H. Milley & Associates
Precast Concrete: Con-Force Structures
Saddledome - 1981-1983
Calgary, AB
The stadium was built to host the 1998 Winter Olympics. The building form is
a 67.7 m radius sphere, intersected by a hyperbolic parabaloid generating the
roofline and a plane to delineate the base. This arrangement provided the absolute
minimum building volume and unobstructed views of the playing surface.
The Saddledome is divided into 5 independent parts: two grandstands having
3 tiers each, 2 grandstands having 2 tiers each and a roof constrained at 2
ends by 4 stability A-frames anchored into rock. The entire structure is of
precast prestressed concrete construction.
The sphere is divided into 32 equal parts by radial columns that support the
ring beam. The ring beam was precast in 16 massive sections which were joined
together with cast-in-place joints and post-tensioning. A 6 m x 6 m grid network
of sagging and hogging cables support 391 lightweight precast concrete roof
panels which were concreted together to form a thin-shell roof.
The roof can freely move on multidirectional bearings (transfer vertical loads
only) on top of the exterior columns. The grandstand structures (concourses
and seating inside the stadium) are all precast and consist of interior framing,
bleacher support raker beams, double tee floor slabs and bleacher slabs. Framing
members were welded and post-tensioned together to resist lateral loads. The
Saddledome was a featured venue when Calgary hosted the 1988 Winter Olympics.
Structural Engineer: Jan Bobrowski and Partners Ltd.
Architect: Graham - McCourt
Precast & Post-tensioning: Con-Force
Olympic Skating Oval
Calgary, AB
The Olympic Oval features a unique precast prestressed concrete, segmental
arch roof that resulted in a world-class lattice arch structure built on a very
austere budget. The actual construction cost was $27 million. The building measures
87.5 m (287-ft) wide by 198.5 m (651-ft) long.
Typical arch segments are 1.8 m deep precast concrete trapezoidal thin-walled
box sections. Typical segment length is 24 m and weight is 48 tonnes. 84 precast
arch segments and 28 perimeter beams were erected on interior scaffolding and
exterior steel truss supports. Interior node joints between the segments were
concreted. The joints were post-tensioned through ducts in the arch segments.
The scaffolding towers were lowered 10 mm at a time in a predetermined sequence
to evenly distribute the load through thrust bearings to the 28 buttresses that
surround the building. This economical solution was built using an existing
precast plant and standard techniques.
Owner: University of Calgary
Architect: Graham - McCourt
Engineer: Simpson Lester Goodrich Partnership
Engineering Review: Dr. Walter Dilger, Dr. Gamil Tadros
General Contractor: W. A. Stephenson Construction (Western) Ltd.
Precast/Post-Tensioning: Con-Force Structures Ltd.
Extruded Hollow Core Slabs - 1962
For many years, hollow core slabs were produced with voids formed by inflatable
rubber tubes. After the concrete had hardened, the air was released and the
tubes were pulled out of the slabs. This was an expensive, labour intensive
process. In 1962, the Spiroll process was invented in Winnipeg under the direction
of Glen C. Booth, Building Products and Coal Ltd. A vibrating machine which
used zero slump concrete, was developed to extrude a hollow core slab over the
prestressing tendons. Today this same process with many subsequent refinements
is used all around the world to manufacture floor and roof building slabs in
a wide variety of widths and cross sections. Approximately 15 million square
feet of these slabs are produced annually in Canada - using enough concrete
every year to build 5 CN-Towers!
CN Tower - 1973 to 1975
Toronto, ON
Truly
a Canadian landmark, the tower at 1815 ft (553 m) is the world's tallest freestanding
structure. Over 1000 tons of prestressing steel was used extensively in the
superstructure of the tower and in the foundation.
The project contains 53,000 cy (40,500 m3) of concrete. The 1450-ft concrete
shaft for the superstructure has a 3-legged cross section that tapers inward.
This shaft was slip-formed in about 8 months under conditions of high winds
and freezing weather.
Tendons were placed, secured, stressed and grouted vertically as the slip forming
continued on a scale never before attempted anywhere. The tower prestressing
is arranged concentrically and designed to disallow tensile stresses under all
estimated dead and live loads and 50-year wind loads.
The shear stresses due to wind are greatly reduced because of the tapering
shape of the tower.
Owner: CN Tower Ltd.
Engineer: Nicolet Carrier Dressel & Associates Ltd.
Architect: John Andrews International, Roger du Toit, Webb Zerafa Menkes Housden
Partnership
Manager / Contractor: Foundation Company of Canada
Post-tensioning: VSL Canada Ltd., Conenco Canada, Dywidag Canada Ltd., BBR Canada
Ltd.
Clinker Storage Silo - 1975
St. Constant, QC
This conical structure is used to store 120,000 tons of cement clinker (which
enters the storehouse at 1200 F) is entirely constructed above ground using
precast prestressed concrete elements. The silo has an inside diameter of 214
ft (65.2 m), a height above ground of 130 ft (29.6 m) and a depth below grade
of 79 ft (24 m). It was estimated the precast prestressed design saved $225,000
in construction and operating costs. The circular structure is divided into
64 equal segments. The precast consisted of 64 identical pieces of: 27 ft (8.2
m) long radial tie beams, 15 ft (4.6 m) long slanted V-columns, 33 ft (10.1
m) lower cone elements, 46.5 (14.2 m) ft long wall panels and 116 ft (35.4 m)
long conical roof elements. Connections were: welding between precast elements
for erection stability and to transfer forces, cast-in-place joints with overlapping
reinforcement for continuity and post-tensioning to join the segments at the
two exterior ring beams. A temporary erection tower supported the upper ends
of the roof elements during construction. This very large and heavily loaded
structure was designed effectively and economically using only five different
types of precast components. The structure is in full use today after 25 years
of service.
Owner: Lafarge
Engineer: William E. Pery, Kilborn Engineering
General Contractor/Precast Supplier: Francon
Construction Manager: Cipriano DaRe
Post-tensioning: Potenco Inc.
CSA A135-1962
Standard for Prestressed Concrete
This
first standard code was published in 1962. The 25-page 3 mm thick document overcame
the last objections to using prestressed concrete in Canada.
The
standard was included in the CPCI Design Handbook by Cazaly & Huggins. Published
in 1964, this was the first precast handbook in North America.
It is not an easy task to pick a mere handful of outstanding prestressed concrete
projects from the thousands of bridges, buildings and other structures built
over the past 48 years. While others may have favorite projects, I hope for
agreement that the ones chosen represent excellence in the design and application
of prestressed concrete.
In our current climate of rapid technological change, it is encouraging to
look back to the early days of prestressed concrete in Canada. A great many
designers and builders immediately recognized the economies, advantages and
design possibilities of prestressed concrete and used courage and imagination
to work with this new material for so many different applications.
References
Huggins, M. W. (Nov.-Dec. 1979) Reflections on the Beginnings of Prestressed
Concrete in America - Part 8 The Beginnings of Prestressed Concrete in Canada
- PCI Journal, Prestressed Concrete Institute, Chicago, IL - V. 24, No.6
Knoll, F., Prosser, M. J., Otter, J. (May-June 1976) Prestressing the CN Tower,
- PCI Journal - V. 21, No. 3
Brancatelli, D., (1984) The Saddledome: The Olympic Ice Stadium in Calgary,
Canada - L'Industria Italiana del Cemento - N. 5
Lester, B., Armitage, H. (Nov.-Dec. 1987) Olympic Oval Roof Structure, - PCI
Journal, V. 32, No. 6
Fowler, J. R., Adams, R. V. (Nov.-Dec. 1986) CPCI Celebrates 25th Anniversary
- PCI Journal, V. 31, No. 6
Nettles, T. A.., Lowe, P.A.R. (Nov.-Dec. 1988) Aerial Guideway for the Vancouver
ALRT Project - PCI Journal, V. 33, No. 5
Pery, W. E. (Jan.-Feb. 1976) Precast prestressed clinker storage silo saves
time and money - PCI Journal, V. 21, No. 1
Fowler, J. R. (Nov.-Dec. 1980) 20 years of progress - CPCI forges ahead -
PCI Journal, V. 25, No. 6
Maranda, L. G. (April 1965) design of Columbia river bridge at Kinnaird, B.
C. Canada - PCI Journal, V. 10, No. 2
