Civil Engineering Reference
In-Depth Information
7.6.12 Effects of Changes in Tubular Member Design
The load calculation underwent a minor change in the new revision of the
design code; however, the most changes were made in the resistance formula
special to the strength of tubular joints, due to the continuous improvement
in the software for finite element analysis.
The average reliability index evaluated for the resistance formulations in
each RP2A edition is presented in
Table 7.8
. The table illustrates clearly that
there has been very little change in the average reliability index over the
years as a result of changes in the equation of resistance. Based on
OTO report
index (1999)
, the average reliability index for the twentieth edition, which is
applicable from the seventeenth edition, is 2.25, and the averages for the various
stress combinations vary from 2.12 for tension and bending to 2.85 for com-
pression, bending and hydrostatic pressure.
By obtaining and evaluating the reliabilities for the early editions, it is found
that the reliability has been influenced by components designed with hydro-
static pressure, which was not included in the early editions. It is important
to know that in the North Sea, structures were not installed in waters over
50 m deep until the mid 1970s, and thus hydrostatic pressure was not a critical
design factor until then.
The average reliability index with the hydrostatic pressure components for
the early editions is shown in
Table 7.9
. The average reliability index due to
changes in the resistance equations has remained virtually constant since
TABLE 7.8
Effect of Change in Resistance Formulations
on the Average Reliability Index, Based on HSE
Date of Code
Average Reliability Index
1969
-
1975
2.15
1975
-
1978
2.3
1978
-
1994
2.25
TABLE 7.9
Effect of Change in Resistance Formulations and
Hydrostatic Component Database on the Average Reliability Index
Date of Code
Average Reliability Index
1969
-
1981
2.25
1981
-
1987
2.32
1987
-
1991
2.25
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