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Deck Restoration
Due to time constraints in the final design phase
of the project, a design-build approach was chosen for the repair
program. Because of the very difficult access to work areas, CFRP
was the only reasonable choice for the strengthening needs of the
project. The successful contractor for the repairs employed an engineer
of record for the CFRP design. In general, the CFRP installation
consisted of applying sheets 10" to 20" (250 mm to 500 mm) in width
at lengths and spacings necessary to develop the full tensile strength
of the material located at the positive and negative moment areas
on the deck.
In order to access the performance of the installed
strengthening system, a full-scale insitu load test was performed.
The load test involved applying concentrated loads by positioning
a forklift on top of the deck. The forklift was loaded with 3,600
lbs (1633 kg) in addition to its own weight for the final load cycle.
This corresponded to a total load on the front axle of 16,600 lbs
(7530kg). The forklift was originally positioned directly above
one of the steel beams supporting the deck, then moved in increments
closer to the mid-span of the slab. As it moved closer to the mid-span,
the deflection of the deck under the wheel loads was monitored.
Figure 1 shows the deflections measured as the forklift moved closer
to mid-span.
These values were then used to compute the curvature of the slab
at mid-span. The curvature of the deck is related to how much the
slab bends under the applied load. Figure 2 shows the bending forces
(moment) required to produce a certain curvature in the slab. By
computing the amount of curvature induced in the slab, the induced
curvature can be compared to the maximum curvature that the slab
can withstand before failure. Figure 2 also shows that the levels
of induced curvature in the slab are well below the failure point.
It may be concluded that the strengthened
slab has safety factor of approximately 6.5 against failure under
the loads used during testing. This safety factor is sufficient
to accommodate higher loads as well as to guard against a brittle,
sudden failure of the slab. The latter is particularly important
in this deck since the original post-tensioning is no longer considered
effective.
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