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Bravo 25 Upgrade Design
The NFESC upgrade design determined a required upgrade reinforcing
areas that was based on an equivalent maximum carbon fiber working
stress of 200 ksi (1,400 mPa) at a strain less than 0.7 percent.
This recognizes strength losses with time and repeated load application.
The NFESC design detailed a high strength carbon fiber area of 0.033
in.2/in.-width (0.083 cm2/cm) for the bottom surfaces and 0.018
in.2/in.-width (0.012 cm2/cm) for the areas on the top surface of
the deck. For a composite laminate with 65 percent carbon fiber,
this translates to a laminate area of 0.051 (0.125 cm2/cm) and 0.028
in.2/in.-width (0.071 cm2/cm) respectively. Table 2 lists the current
flexural capacities of the subject members as well as the target
upgrade capacities. All upgrade reinforcement materials were required
to be compatible with ordinary concrete as well as polymer concrete
with 12.5 pH and to not adversely effect the titanium-based cathodic
protection system. The design life of the upgrade was 20 years without
significant degradation. The contractor installed the following
reinforcement selections:
| · |
Top Reinforcement: pultruded, 3/8-inch diameter (9.6 cm),
high-strength carbon composite bars encapsulated by epoxy in
slots cut into the concrete surface. |
| · |
Bottom Reinforcement: Hand lay-up, prepregged, uniaxial, carbon
fiber tow sheets with epoxy matrix. |
Table 2. Flexural Capacities of Bravo 25 Deck Elements
| Members |
Direction |
Moment
Sign |
Current
in-kips/ft |
Upgrade
in-kip/ft |
%
increase |
| 13-1/2" deck (top) |
Transverse |
Negative |
Corroded |
600 |
-- |
| 13-1/2” deck (bottom) |
Longitudinal |
Positive |
Unreinforced |
549 |
-- |
| 8-1/2” deck (bottom) |
Transverse |
Positive |
222 |
312 |
41 |
8-1/2” deck (bottom) |
Longitudinal |
Positive |
110 |
216 |
96 |
| Track slabs (bottom) |
Longitudinal |
Positive |
1,480 |
1,735 |
17 |
Track slabs (top) |
Longitudinal |
Negative |
846 |
990 |
17 |
|
In accordance with NFESC drawings and specifications, the contractor
bonded tow sheets in the longitudinal direction of the bottom of
the deck between the continuous outboard girder and the curb and
the bottom of the track slabs (Figures 47 and 48).
Transverse, carbon laminate reinforcement was bonded to the bottom
of the deck between the track slabs (Figures 47 and 49).
Carbon/epoxy rods were embedded in the transverse direction to reinforce
the top of the 13-1/2-inch (34 cm) deck over of the outboard girders
to the curb and in the longitudinal direction to reinforce the top
of the track slabs over the transverse girders (Figures
47 and 50). The deck areas with large utility openings
near the curb were not reinforced since outriggers cannot be placed
on these locations.
Figure 47. Section view of basic locations of upgrade reinforcement.
Figure 48. Plan view of basic locations of longitudinal upgrade
reinforcement on bottom deck and rail stringers.
Figure 49. Plan view of transverse upgrade reinforcement on bottom
deck between rail stringers.
Figure 50. Plan view of basic locations of longitudinal upgrade
reinforcement on top deck.
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