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SkyTrain Millennium Line
Vancouver, BC
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SkyTrain Millennium Line
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Precast concrete segmented box girders
enabled the Millennium Line project to remain on schedule
and under budget. |
The SkyTrain Millennium Line extension is a 10-mile precast concrete
segmental box girder aerial structure that adds to the existing
SkyTrain automated guideway system in Vancouver, British Columbia,
Canada.
Superstructure
The Millennium Line uses a single-cell, precast concrete segmental
box girder. The cross section of the segment was designed to be
torsionally stiff, allowing the construction of long spans through
curved sections of the alignment. Each guideway beam was typically
120 feet long, 7 feet deep, and consisted of twelve 25-ton concrete
segments.
About 5,700 concrete segments were cast at a special facility constructed
for the Millennium Line. The segments were stored at the facility
and moved to their erection sites using flatbed trucks. Each segment
was unique to fit the horizontal and vertical geometry of the guideway
rails in the section for which it was destined. Each segment took
one day to form and cast, using about 13 cubic yards of concrete.
The job was a massive undertaking, requiring about 130,000 cubic
yards of concrete. Even so, construction of approximately 10 miles
of standard elevated guideway was finished in only 16 months.
Most of the guideway, which is designed for a 100-year lifespan,
was built along existing rail and highway corridors and features
an unprecedented and unique application of truss-erected segmental
precast guideway construction. Four of the massive 200-ton overhead
erection trusses, with lengths in excess of 325 feet, were used
to build the guideway. Standing on the guideway’s support
columns, the launching girders raised precast guideway segments
into place. Crews then threaded steel post-tensioning tendons through
the concrete segments to form self-supporting beams wide enough
to carry the two SkyTrain tracks.
The inserts for rail fasteners were cast into the segments at the
plant, and then the trackwork was laid directly on the structural
concrete. After the spans were erected, the elevations were surveyed,
the profile grade was adjusted, and shims were introduced beneath
fasteners as required. The average shim thickness for the entire
project was less than 1/4 inch. This is the first application of
direct fixation rail onto a segmental constructed guideway without
the use of plinths.
Substructure
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The substructure consisted of cast-in-place
caissons and columns. |
More than 500 cast-in-place concrete columns support the Millennium
Line elevated guideway. The support columns are eight-sided and either
5 feet, 3 inches or 6 feet, 10 inches wide (wider at SkyTrain stations
and some other locations). The columns flare out at the top to meet
the inward angle of the guideway segments placed above them. About
26 cubic yards of concrete was required to build an average column.
The foundations that hold the columns were typically created using
drilled pier technology: steel casings with a diameter of 6 feet,
6 inches were vibrated into the ground, the earth was then augured
from the center of the casing, a reinforcing steel cage was lowered
into the casing, and concrete was placed. In areas where it was appropriate,
spread footing foundations were used instead of drilled piers.
Unique Station Designs
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Concrete was used for substructure
elements at each of the unique stations along the extension. |
The Millennium Line’s 13 stations are key to the success of
the expanded rapid transit system. Each station is unique and was
designed by British Columbia’s prominent architects and structural
engineers, with input from an extensive public consultation process.
Designed to be futuristic while complementing the communities in
which they are located, the stations are built with provisions for
public amenities and security features to ensure that commuters
of all abilities and ages can use the line safely and efficiently.
Stations are all constructed primarily with concrete elements up
to the platform level. Columns and foundations are constructed with
cast-in-place concrete, and the platforms are carried with precast
concrete beams. The station ancillary cores utilize architectural
concrete blocks.
The first section of the Millennium Line was turned over to the
operating authority in December of 2001, with the balance of the
line completing operational testing in August of 2002, less than
three years after groundbreaking. The project is forecast to be
completed on budget and within the established construction schedule,
and once fully operational, the Millennium Line will have approximately
20 million riders annually by 2003. The total project cost was $1.1
billion in Canadian dollars.
Project Credits
Location: Greater Vancouver, British Columbia, Canada
Owner: RTP 2000 Ltd.
Engineer: Earth Tech
Contractor: SAR Transit JV
Concrete Supplier: Lafarge Canada
Precaster: SAR Transit JV
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