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normal patterns sooner. This is particularly important where a convenient detour
is not available, such as in rural areas, or in regions, such as the Puget Sound,
where most highways are already operating near or over their intended capacities,
leaving nowhere for additional traffic to go.
2. Reduced Impact on Traffic Flow. Construction methods that allow portions of
the bridge to be built off-site and then erected quickly on-site can significantly
reduce the negative impacts of on-site construction. In many cases, prefabricating
elements allows the on-site work to be completed during night and weekend
hours, when traffic volumes are lower. This consideration is critical in urban
areas.
Bridge designs that can be constructed rapidly are particularly useful when a
bridge is unexpectedly put out of service because of a vehicular collision, earthquake, or
other disaster. This was illustrated by the I-65 Bridge over I-59 in Birmingham, Alabama
(Barkley and Strasburg 2002). In 2002, a gasoline tanker collided with one of the piers of
the I-65 Bridge. The impact and ensuing fire damaged the bridge beyond repair. With
user costs from the closed bridge estimated at over $100,000 a day, the Alabama
Department of Transportation implemented a rapid construction solution that replaced the
bridge in only 53 days (Barkley and Strasburg 2002). Less than three years later, a similar
accident occurred less than one-half mile from the I-65 bridge, and the replacement
bridge was designed, fabricated, and constructed in 26 days (Endicott 2005).
Cast-in-place concrete bridges have been used extensively in Washington State.
Bridges constructed with cast-in-place concrete substructures, prestressed concrete
girders, and cast-in-place concrete decks have a good service record in terms of durability
and seismic performance; however, these bridges require lengthy construction periods.
Multiple concrete pours are required, and each pour must be allowed to cure before
construction can proceed. Construction activities associated with cast-in-place concrete, including the construction of falsework, placement of formwork, tying of reinforcing
steel, and removal of formwork, also increase construction time and must be completed
on-site where traffic patterns may be disrupted. This project aims to develop alternative
bridge designs that can be constructed rapidly while preserving the durability and seismic
performance exhibited by cast-in-place bridges.
1.2 PRECAST CONCRETE COMPONENTS: A POTENTIAL SOLUTION
Bridge designs incorporating precast concrete components are a potential solution
for providing rapid construction. Precast concrete components are reinforced concrete
members that are fabricated off-site, either in a fabrication plant or staging area, and then
brought on-site and connected together. The number of on-site construction tasks is
significantly reduced when precast concrete is used because the building of formwork,
tying of reinforcing steel, and pouring and curing of concrete for many of the components
can be completed off-site. Reducing the amount of work that must be done on-site
reduces traffic disruption, especially because the precast components can usually be
erected and connected at night. The overall construction time on-site can be reduced by
using precast concrete components because the components can be fabricated in advance,
eliminating the time spent waiting for concrete to cure.
Incorporating precast components into bridge designs can also provide several
secondary benefits. They include the following:
• improved worker safety because the on-site construction time, during which
workers are potentially exposed to high-speed traffic, is reduced
• higher quality members with better durability because of stringent quality control