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West
Mission Bay Drive is a primary arterial link between the
communities of Point Loma, Ocean Beach, and Pacific Beach,
in the City of San Diego. The West Mission Bay Drive Bridge
traverses the main channel of Mission Bay between Dana Point
and Pacific Beach. The structure is 1,200' long pre-cast
concrete girder bridge build on eight caps, supported by
16 columns, with two columns per bent, each column supported
by four existing batter pile per footing.
This
project, with Tralyor Pacific as General Contractor, jointly
funded by Caltrans, FHWA, and the City of San Diego, is
the seismic retrofit of the existing structure. The scope
of this project involves a substantial retrofit of the existing
footings, as well as stiffening of the existing columns,
the addition of restrainers at the hinges, and concrete
catcher beams at the abutments.
The
sixteen columns on this structure called for the addition
of tightly spaced #8 hoops from top to bottom with the addition
of 8-inches of new cast-in-place formed concrete. Truesdell
Corporation was able to convince the owner to allow the
placing of column concrete by shotcreting. First a prototype
mockup of one of the projects columns was constructed and
shot in Phoenix, Arizona. After the mockup was successfully
shot, and accepted by the Resident Engineer, Truesdell was
allowed to conditionally shoot the first two of sixteen
columns. Truesdell was successful and was allowed to shoot
all sixteen columns with shotcrete. Placement of the column
concrete by shotcreting reduced the overall cost to the
project and improved the column schedule by eliminating
the placement and stripping of forms, and allowing the column
work to progress independent of the footing retrofit work.
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