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Analysis of Bravo-25 Load Response
NFESC utilized detailed finite element analysis (FEA) modeling
to characterize the structural behavior, determine reinforcement
requirements, and verify proposed upgrade reinforcement designs.
Finite element models were optimized and calibrated with the Impact
Load Method (ILM) test results of 1996. They were further modified
to reflect the additional CFRP reinforcement and were used to predict
the load response of the as-built, upgraded structure.
The FEA program, STARDYNE, was used in the analysis. A detail of
the FEA modeling is shown in Figures 41 through 45. The models are
composed of three-dimensional elements representing portions of
the deck and all girders, orthogonal shell elements for the remaining
deck areas, beam elements for the piles and utility loops, and rods
for the reinforcement bars. Two sets of models with the same overall
geometry were developed. The first represented the pier in its original
condition validated to match the ILM response and the second represented
the pier in the upgrade configuration (e.g., Figure 45). Reinforced
concrete properties were obtained from the ILM testing. The original
FEA models provided flexure and shear response of the pier due to
mobile crane operations. Using the FEA results, NFESC determined
strength increases necessary to meet the additional demands of 70-ton
(64 metric ton) crane operations over the existing capacity.
The upgrade FEA model set included the stiffness effects of the
added carbon reinforcement. Carbon composite mechanical properties
used in the FEA models were obtained from coupon tests using carbon
fibers with a minimum ultimate strength of 500,000 psi (3,4500 mPa)
and a minimum Young’s modulus of 30,000 ksi (207,000mPa).
Additional stiffness restrictions were imposed to control deflections,
mitigate crack growth, and minimize crack width. Table 1 contains
the maximum flexural response to 130-kip (580 kN) outrigger loads
in the upgraded slabs.
Figure 41. Top view of Bravo 25 finite element model detail with
access hole cut in curb deck and patch load applied near curb.
Figure 42. Bottom view of Bravo 25 finite element model detail.
Patch load applied to center slab.
Figure 43. Cross section detail with load applied near curb.
Figure 44. Model cross section detail with outrigger load on midspan
of center slab.
Figure 45. Finite element model detail of upgraded Bravo-25. Carbon
rods installed on top surface.
| Table 1. Outrigger Load Response of Bravo 25 Deck
Elements |
| Member |
Location |
Direction |
Moment
Sign |
Max Flexure
in-kips/ft |
Shear
kips/ft |
| 13-1/2” curb deck |
Edge of pile girder |
Transverse |
Negative |
102 |
25.0 |
13-1/2” curb deck |
Edge near curb |
Longitudinal |
Positive |
52 |
|
| 8.5” center deck |
Midspan |
Transverse |
Positive |
130 |
19.5 |
8.5” center deck |
Midspan |
Longitudinal |
Positive |
95 |
|
| 8.5” center deck |
Edge of transverse girder |
Transverse |
Positive |
80 |
|
| Track slabs |
Edge of transverse girder |
Longitudinal |
Negative |
200 |
26.0 |
| Track slabs edge |
Midspan |
Longitudinal |
Positive |
295 |
|
|
