Offshore Structure Platform Design - Offshore Structures: Design, Construction and Maintenance - page 160

The nominal brace stress range should be based on the section properties of
the brace-end under consideration, taking due account of the brace-stub, or a
flared member end, if present. Similarly, the SCF evaluation should be based
on the same section dimensions. HSSR is the hot spot stress range.
The nominal cyclic stress affecting the chord may also influence the HSSR
and should be considered. The SCF should include all stress-raising effects
associated with the joint geometry and type of loading, except the local micro-
scopic weld notch effect, which is included in the S-N curve. SCFs may be
derived from FE analyses, model tests or empirical equations based on such
methods. In general, the SCFs depend on the type of brace cyclic loading if
the axial load applied to the brace is in-plane bending or out-of plane bending,
the joint type and details of the geometry. The SCF varies around the joint, even
for a single type of brace loading.
When combining the contributions from the various loading modes, phase
differences between them should be accounted for, with the design HSSR at
each location being the range of hot-spot stress resulting from the point-in-
time contribution of all loading components.
In general, for all welded tubular joints under all three types of loading, a
minimum value of SCF equal to 1.5 should be used.
For unstiffened welded tubular joints, SCFs should be evaluated using the
Efthymiou equations, as will be discussed later in thickness effect on the SCF.
The linearly extrapolated hot-spot stress from Efthymiou may be adjusted to
account for the actual weld toe position, where this systematically differs from
the assumed AWS basic profiles.
The SCF applies also to internally ring-stiffened joints, including the stresses
in the stiffeners and the stiffener-to-chord weld. Noting that special consideration
should be given to these locations, SCFs for internally ring-stiffened joints can be
determined by applying the Lloyd s

Report (1988) to the SCFs for the equivalent unstiffened joint. For ring-stiffened
joints analyzed by such means, the minimum SCF for the brace side under axial
or OPB loading should be taken as 2.0.

' s reduction factors based on the Lloyd '

SCFs in Grouted Joints
Grouted joints are usually used in repairing or strengthening the platform.
Grouting joints tends to reduce the SCF of the joint, since the grout reduces
the chord deformations. In general, the larger the ungrouted SCF, the greater
the reduction in SCF with grouting. Hence, the reductions are typically greater
for X and T joints than for Y and K joints. More discussion of the effect of
grouting on strengthening is presented in Chapter 7 .

S-N Curves for All Members and Connections
For nontubular members and connections in deck structures, appurtenances and
equipment and tubular members and attachments to them, including ring stiffeners,