Civil Engineering Reference
In-Depth Information
Topside Weight Change
This factor accounts for the likelihood of failure of the platform due to changes in
deck weight due to deck extensions, additional static or rotating equipment or
change of use. Defining deck weight change is not easy for platforms from the
past (e.g., over 40 years old) because, without computerized archives of drawings
and reports, it is very difficult to make the calculations. The main sources of data
are the original drawings, if they still exist, the actual condition of the platform, and
collection of information from people who worked on the platform before.
There are four possible scenarios: you have no data at all; you have minor data
but you cannot know if the weight has increased or decreased from the original;
you have data and estimate that the growth in weight has been less than 10%; or
you estimate the weight growth has been more than 10%. The score for this factor
is shown in
Table 8.21
.
Additional Risers, Caissons and Conductors
This factor is intended to account for the effect that additional risers, caissons
and conductors (over and above those that the structure was originally designed
for) have on the likelihood of failure of the platform.
The score depends on both the number of risers, caissons and conductors
that the structure was designed for and the additional number subsequently
installed (
Table 8.22
). Note that the overall weight of the total score is 5.
If there is uncertainty concerning the basis of the original design, a con-
servative estimate of the number of additional risers, caissons and conductors
is used.
If you have the diameter of the original riser and conductor design and the
diameters of the actual existing riser and conductors, this factor can be calculated
by obtaining the ratio of the sum of the diameters of the existing risers and
conductors to the sum of the diameters for the original design of conductors
and risers.
TABLE 8.21
Topside Weight Change
Criteria
Score
Not known if weight has increased or decreased
2
Estimated weight growth
≤
10%
5
Estimated weight growth
>
10%
8
No data
10
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