Civil Engineering Reference
In-Depth Information
TABLE 8.17
Remaining Wall Thickness
Remaining Wall (%)
Score
>
≤
50
10
50
80
8
80
99
3
100
0
Number of Members
Weight
≥
≤
4
0.2
5
9
0.4
10
1
Total score = tabulated score
×
weight
damaged and flooded members, since the remaining wall is the key factor.
Remaining wall is expressed as a percentage of the nominal thickness.
Table 8.17
presents a score between 0 and 10, where a score of 0 corre-
sponds to a wall retaining 100% thickness and a score of 10 corresponds to a
wall that has thinned to less than or equal to 50%. This score is then multiplied
by another factor that is determined by the number of members thinned. The
resulting scores range from 0 (no risk of failure) to 10 (increased risk of failure).
The overall weight of this factor in the total score is 7.5.
The remaining wall and the extent are both inspection results. Consequently,
the corrosion factor is taken as a strong indicator of the current condition of the
platform.
However, for this factor, the effect on likelihood of failure has been kept
independent of bracing pattern and number of legs, because a member with a
corroded wall would still be considered to be contributing to the structural stiff-
ness and thus would carry load with a reduced capacity. When the remaining
wall turns into a through-thickness hole, a crack or a dent, it would be re-cate-
gorized as a damaged member, for which separate qualitative calculations exist,
as described above.
Likelihood Calculation for Load
Design Loading
Previous studies concluded that the first generation of platforms in the Gulf of
Mexico were designed for a hydrodynamic loading that is 55% of today
'
s
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