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44 OCTOBER 2013 Concrete international
Texas Builds Worlds
First Precast NetworkArch BridgeProject to be completed in time
for upcoming holiday season
The worlds first precast network arch bridge is changingthe
landscape o downtown Fort Worth, TX. With itsseries o sculpted
network arches and modern architec-
ture, the new bridge will serve as the entrance to the
citysvibrant downtown and cultural district, where
buildingsdesigned by luminaries such as Louis Khan, Tadao Ando,and
Renzo Piano line the landscape.
The Texas Department o Transportation (TxDOT) has along history
o building durable, high-strength, precastconcrete bridges quickly
and at costs that consistently rankamong the lowest in the nation.
The innovative design othe Fort Worth bridge met the challenges o
quick construc-
tion, aesthetic beauty, and improved mobility and saetywhile
also providing a large hydraulic opening to mitigateflood
conditions.
The West 7th Street Bridge design and constructiontechniques are
urther examples o Texas leading the way ininnovation, said TxDOT
Executive Director Phil Wilson.In addition to being an
architectural and engineeringlandmark or the city o Fort Worth,
this precast networkarch bridge is a sae, sound, and high-quality
structure thatwill benefit both motorists and businesses.
This elegant and sophisticated signature bridge willspotlight
Fort Worth, the nations 16th largest city and
growing, said Fort Worth Mayor Betsy Price. Its going tobe a
beautiul asset or the city.
The idea was to turn to our successes in precast technol-ogy and
mass productiononly, we knew we wantedsomething more attractive or
the West 7th Street Bridge,said TxDOT Structural Engineer Dean Van
Landuyt.Aesthetics were paramount. We tried to do somethingworthy o
the great buildings and great architects who haveworked in the
city.
The new $26 million West 7th Street Bridge will replaceits
100-year-old predecessor with a unique and beautiuldesign that
offers much more pedestrian access. The bridge
will be 981 f (299 m) long and 88 f (27 m) wide, have our
lanes, and have two 10.5 f (3.2 m) pedestrian/bicycle
pathsoutside the 12 arches.1
Each arch is 163.5 t (50 m) long, weighs 300 tons(272 tonnes),
and will rise over 20 f (6 m) above theroadway surace at the
highest point. A network o stainless steelhangers with clevises and
tie-beam connections will protectpedestrians rom traffic while
allowing both motorists andpedestrians to enjoy a nearly
unobstructed view o the river.
Side Cast
The contractor, Sundt Construction, Inc., o SanAntonio, TX,
began work over a year ago with little to no
impact on motorists and businesses. The arches wereconstructed
at a nearby casting yard donated by ChesapeakeEnergy. Each was cast
lying flat on its side. While still in thatposition, initial
post-tensioning was applied and thestainless steel hangers were
installed. When the concretereached 6000 psi (41.4 MPa), the arch
was rotated to thevertical, the remainder o the post-tensioning
specified orthe arch tie was applied, and the nuts on the hangers
weretightened completely. Thus, when the rams were removed,the
hangers were loaded approximately equally. Thecompleted arch was
then slid to a storage area, ready ortransport and placement.
This spring, all 12 arches were transported (Fig. 1) andset on
columns located beside the original bridge prior toits closure and
removal. Over the summer, traffic on thebridge was detoured onto an
adjacent city street so theprecast beams and deck panels could be
set, ollowed byinstallation o a concrete slab and stainless steel
hand rails.
This new construction method is expected to result inonly 5
months o bridge closure, compared to a typical12 months or more
using traditional methods. Theestimated project schedule is shown
in Fig. 2.
Visit http://fortworthtexas.gov/SeventhStreetBridgeor updates on
the West 7th Street Bridge project. TxDOT is
responsible or maintaining 80,000 miles (128,748 km) o
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Concrete international OCTOBER 2013 45
road and or supporting aviation, rail, and public
transpor-tation across the state. TxDOT and its 11,000 employees
arecommitted to working with others to provide sae andreliable
transportation solutions or Texas by maintaininga sae system,
addressing congestion, and connectingTexas communities.
References
1. Seventh Street Fact Sheet, http://fortworthtexas.gov/
uploadedFiles/Transportation_and_Public_Works/Projects/
130604_factsheet.pdf. (last accessed Aug. 14, 2013)
Selected for reader interest by the editors.
Fig. 2: Estimated project schedule for the West 7th Street
Bridge1
Fig. 1: Installation of one of 12 precast arches for the West
7th
Street Bridge in Fort Worth, TX. Each arch is 163.5 ft (50 m)
long,
weighs 300 tons (272 tonnes), and will rise up to 20 ft (6 m)
above
the roadway. The precast girders (strong backs) above each
end of the arch were installed prior to final stressing of the
tie
and hangers. They will remain in place until the bridge deck
and
beam dead load counteracts the tie force
January 2012
January 2013
May 2013
June 2013
Fall 2013(weather permitting)
November 2013(estimated)
BEGIN PROJECT OFF-SITE
BEGIN ON-SITE CONSTRUCTION
CLOSE SIDEWALK & OUTSIDE LNs
CLOSE BRIDGE TO TRAFFIC
OPEN NEW BRIDGE TO TRAFFIC
PROJECT COMPLETE
Activities Pre-cast bridge elements off-site Move utilities
Stock Show & Rodeo
Activities Place traffic barrier Set & brace arches
Activities Demolish old bridge Set floor beams & panels
Complete bridge slab
Final work under new bridge
Legend Intermittent, short-term lane closures Bridge reduced to
one-lane each direction Total bridge closure thru traffic detoured
to Lancaster
