Assessment of Existing Structures and Repairs - Offshore Structures: Design, Construction and Maintenance - page 453

7.2.3 Member Resistance Calculation
As discussed by OTO report index (1999) , there were only been three occur-
rences of major changes to the member resistance equations in RP2A. The
first was the introduction of member resistance formulations into RP2A in
the sixth edition (1975). Before then, RP2A had recommended that the AISC
provisions be used. Guidance for local buckling was introduced, along with
provisions for hydrostatic pressure, and interaction equations for axial compres-
sion and bending stress and axial tension and hoop stress.
The second change was with the publication of the eleventh edition (1980).
Equations were introduced for the assessment of allowable hoop stress, rather
than using a design chart, and a formulation for the combined effects of axial
compression, bending and hydrostatic pressure was introduced.
The third change occurred in 1987, with the introduction of the seventeenth
edition, where a major change was made in the allowable bending stress, which
was increased from 0.66 F y to 0.75 F y for members not susceptible to local
buckling.
Finally, in 1993, the first edition of API RP2A-LRFD introduced some
equations that had been modified. The modifications have not yet been intro-
duced into the WSD version, and the member resistance formulations in the
twentieth edition (introduced at the same time as LRFD) are identical to the
those in the nineteenth edition.
7.2.4 Joint Strength Calculation
There have been ongoing changes in the recommendations for tubular joints due
to continuous research and development. The first edition recommends that
connections be designed to develop at least 50% of the effective strength of
the members. However, in the first two editions of RP2A, no provisions for tub-
ular joint strength were given except for a mention that the design and detailing
of joints should be in accordance with good current practice. Not until the third
edition (1972) was some specific guidance given for joint strength design. This
was based on the punching shear concept, and it was very simplistic. The fourth
edition (1972) introduced factors into the allowable stress formula to allow for
the presence of load in the chord and the brace-to-chord diameter ratio.
However, not until late 1977, with the publication of the ninth edition, was
allowance made in the allowable stress formulation for the joint configuration,
such as T, X or K. A plastic reserve factor was also introduced to account for
interaction between brace axial and bending stress; however, this term was later
dropped in the fourteenth edition.
The fourteenth edition (1984) added a major change in joint design recommen-
dations because new test data had proved that the previous API joint strength equa-
tions and guides were un-conservative. Therefore joint design based on the
fourteenth edition is different than design based on the previous editions and earlier