By: Bill Wilson
Fight big with big. Designers of the San Francisco-Oakland
Bay Bridge East Span Replacement (Oakland Skyway Project) were presented the
task of creating a structure hefty enough to withstand the largest earthquake
event on the planet.
"It has to survive intact because it's needed for
emergency personnel to make it from Oakland to San Francisco," Scott
McNary, project manager for Parsons, told Roads & Bridges. "When that
big earthquake hits, all you'll see is a little bit of cracking."
The Oakland Skyway Project is the top hit of R&B's 2003
Top 10 Bridge list, marking the second time the San Francisco-Oakland Bay
Bridge East Span Replacement project has earned such recognition. The
cable-stayed portion of this engineering feat was No. 1 in 2001.
At $1.04 billion, the Oakland Skyway Project is the largest
contract ever awarded by the California Transportation Department (Caltrans).
The precast segmental bridge comes with enormous specifications. In order to
create sound footing crews are hammering 300-ft steel tubular piles 8 ft in
diam. with a 2-in.-thick wall through 100 ft of bay mud. After the piles are
set, massive steel footings will be constructed followed by concrete columns
and the superstructure.
The precast concrete pieces, currently being produced at a
yard about 80 miles away in Stockton, Calif., dominate the size of normal
40-ft-wide by 10-ft-long sections. The ones destined for the Oakland Skyway
Project are designed to be 82 ft wide, 26 ft long and weigh 800 tons. After a
barge trip to the site, super-sized equipment move the pieces in place. Locking
the concrete together are steel cables and a slow-curing, hard-gripping epoxy
spread to 1?16 of an in. on each joining segment.
"The winch mounted on the bridge to hoist the segments
is probably larger than a house," said McNary. "It was a design
decision (for the bigger pieces) made early on in the project. The most
efficient way to build this bridge would be to use large pieces, and it was
felt that because there was water access (from the precast yard) you could
handle the large pieces. What it means is you could build a lot of bridge
fairly quickly."
As of press time about 50 of the total 450 precast pieces
had been delivered and about half of the piles were in place. The first two of
the 28 concrete columns were up, and superstructure erection is scheduled to
begin in late spring 2004.
2. Bill E. Emerson Bridge
Cape Girardeau, Mo.
It's not easy to stand in the Mississippi River, especially
during an earthquake. The Bill E. Emerson Bridge is 3,956 ft long and composed
of a three-span, 2,086-ft steel and concrete composite cable-stayed unit.
Located 50 miles from a major fault line, the span is designed to withstand a
major earthquake event.
3. Victory Bridge
Middlesex County, N.J.
One may not be able to smell Victory, but they can certainly
see it. The New Victory Bridge will feature a 440-ft-long precast match cast
concrete main span and a 355-ft horizontal navigational channel. Four World War
I memorial obelisks will be on display at the bridge abutments.
4. Maybank Bridge
Charleston, S.C.
Soon motorists will be able to cross the Stono River without
hesitation. The Maybank Highway Bridge will replace a swing span bridge which
causes traffic to wait through open/close cycles. The new stretch will be 65 ft
tall and 90 ft wide.
5. Four Bears Bridge
New Town, N.D.
Three Indian tribes--Mandans, Hidatsas and Arikaras--will
show their colors on the Four Bears Bridge in North Dakota. The 4,500-ft-long
span will honor the three groups with a linear library along a pedestrian
walkway and tribal medallions above the piers. The bridge is designed to handle
severe ice loadings. The project was bid at $55 million.
6. New Julien Dubuque Bridge
Dubuque, Iowa
A tied-arch bridge will secure the historical integrity of
the existing Julien Dubuque Bridge. The 5,635-ft structure, which must be
differentiated from the existing and be compatible with the historic features,
etc., will feature a composite floor/tie system, a continuous deck and bolted,
high-performance steel girders. The project carries a price tag of $160
million.
7. Pearl Harbor Memorial Bridge
New Haven, Conn.
The Pearl Harbor Memorial Bridge is the first dose of new
engineering in the U.S. This extradosed prestressed bridge has a main span of
515 ft. There are 24 extradosed prestressed bridges in the world, with the
Pearl Harbor serving as the first one on home soil. The bridge resembles a
cable stay, but behaves like an externally prestressed girder bridge.
8. Ocean City-Longport Bridge
Ocean City, N.J.
The Garden State's newest bridge is 3,450 ft long and
carries two lanes of traffic. The 26-span structure cost $52 million to build.
9. I-95 Airport Access Bridges
Philadelphia, Pa.
The fastest growing airport now has the interstate firepower
to handle an increase in traveler load. The $80 million project featured a 1,440-ft-long
viaduct which provides the direct link from I-95 to the Philadelphia
International Airport.
10. Wakota Bridges
St. Paul, Minn.
The Wakota Bridges are two parallel, 1,900-ft-long segmental
concrete box girder bridges that will carry I-494 over the Mississippi River.
Design considerations included accommodating a deck that is 50% wider at the
abutments than in the center.
