About Access. Suspended metal decking (above) and
a "stairway to heaven" made of steel channels
(left) help contractors easily reach work areas. (Photos
by Michael Goodman for ENR)
Contractors are almost
complete with the second phase of a planned decade-long, $392-million
effort to keep San Franciscos storied Golden Gate Bridge
in place for future generations of span users and lovers.
The complex seismic retrofit of the link to Marin County,
Calif., is "a little like brain surgery," says Ewa
Bauer, deputy district engineer for the Golden Gate Highway
and Transportation District, the public agency that built
the bridge in 1937, and now operates and maintains it. "We
must modify the system but be cautious not to destroy the
intricate structure already in place," she says.
The current $122.3-million contract
for work at the bridges southern approach, which began
in mid-2001, includes complete replacement of bottom lateral
bracing and vertical supports for the viaduct. It also covers
construction of internal shear walls and replacement of the
west wall of the anchorage house. New bearings and energy
dissipation devices are being installed in the 320-ft-long
arch that carries the road deck over the Civil War-era Fort
Point, and the archs steel members are being replaced
and strengthened. Finally, some 5 million lb of steel plate
are being installed on two sets of approximately 220-ft-tall
concrete pylons at either end of the arch.
The catalyst for the retrofit was
the 1989 Loma Prieta earthquake. The span suffered no "observed"
damage from that temblor, but a subsequent vulnerability study
determined that consequences of a quake of Richter magnitude
7.0, with a nearby epicenter, could be more severe. A temblor
of 8.0 or greater could cause collapse of key structures,
such as both approach viaducts and the Fort Point Arch.
Much of work site is directly above a Civil War-era fort.
(Photo by Michael Goodman for ENR)
The retrofit aims to upgrade the
1.7-mile-long span so that it will suffer only minimal damage
in the equivalent of an 8.3 quake on the San Andreas fault,
seven miles west of the bridge. Work must be accomplished
without closing the bridge or altering its historic appearance.
"It must be done in such a way so that people will say
nothing is really happening here," says Bauer.
Although current work is being performed
over land, material layout area is limited. Construction is
concentrated within a compact area bound on the west by the
Pacific Ocean and east by steeply sloping terrain. Workers
are hampered by the notoriously changeable and sometimes severe
San Francisco weather that includes strong wind, high waves
Because the site is a tourist attraction
and a vital transportation link, contractors must contend
with work hour restrictions. "More limitations are stacked
upon limitations," says Paul Cocotis, president of Shimmick
Construction Co. Inc., Hayward, Calif. A joint venture of
his firm and Obayashi Corp., San Francisco, is general contractor.
The projects second phase is 90% complete and on schedule.
Work is within 3% of the bid price, and contractors have used
only a small portion of the contingency.
But progress has not been blemish-free.
In 2002, Kevin Noah, a joint venture carpenter, died when
he fell about 50 ft while working in the anchorage house.
The contractor appealed $26,025
in penalties for one general and three serious citations issued
in 2003 by the California Occupational Safety and Health Administration.
That process is on hold, pending outcome of a criminal probe
by the San Francisco district attorneys office. "If
[it] chooses not to prosecute, the appeal process will move
forward," says a Cal/OSHA spokeswoman. Neither the owner
or Shimmick-Obayashi will comment.
Other issues have plagued the overall
project. First phase work, which had a different contractor
and design team, called for retrofitting several structures
that make up the bridges north approach. But when work
was completed in 2001, it cost nearly double the original
1997 contract amount of $30 million (ENR 11/27/00 p. 15).
Domain. Bauer surveys Golden Gate from top of north
suspension tower. (Photo by Michael Goodman for ENR)
Officials say relations are much improved
in the current phase. "There is no you bid on this
job, it is your problem," says Bauer. Participants
point to a clear and complete set of contract documents for
providing a solid foundation for the job.
The key to the current phases
success is "plans that contractors want to build,"
says Thomas Jee, president of his own San Francisco-based
firm and the projects engineer of record. Sverdrup Civil
Inc., St. Louis, is prime engineering consultant. Jee had
been Sverdrups project manager for the Golden Gate job.
courtesy of Golden Gate Bridge Highway and Transportation
One improvement over phase one
was incorporating foundations for the south viaducts
temporary vertical supports into the permanent foundation
retrofit, say engineers. The 714-ft-long viaduct superstructure
is supported by a set of three girder spans and a set of three
truss spans. These sit on a series of bents and towers now
being completely replaced.
here to view drawing
Engineering documents required
removing only one vertical support at a time and specified
the order of replacement. Contractors started with Tower 3,
the support closest to the Fort Point Arch, followed by the
adjacent Tower 2. (
here to view drawing) They then replaced the bents and
are now completing replacement of the last support, Tower
Before replacement, existing foundations
were strengthened and enlarged to accommodate seismic forces.
They were also designed to support temporary adjustable and
reusable towers erected to the side of bents and existing
towers, prior to removal. This differs from the earlier north
viaduct retrofit, where separate...