Offshore Structure Platform Design - Offshore Structures: Design, Construction and Maintenance - page 159

Heavy wall section of chord

Offset not to
exceed ± D/4

D/4 or 30 0 mm
Minimum

D/4 or 30 0 mm

Minimum

d or 600 mm

Min 50

FIGURE 3.38 Hot spots at in-plane tubular joint.

SCFs may be derived from finite element (FE) analyses, model tests or empiri-
cal equations based on such methods. When deriving SCFs using FE analysis, it is
recommended to use volume (brick and thick shell) elements to represent the weld
region and adjoining shell, as opposed to thin shell elements. In such models, the
SCFs may be derived by extrapolating stress components to the relevant weld toes
and combining them to obtain the maximum principal stress and, hence, the SCF.
The extrapolation direction should be normal to the weld toes.
According to Healy and Buitrago (1994) and Niemi et al. (1995) ,ifthin
shell elements are used, the results should be interpreted carefully, since no sin-
gle method is guaranteed to provide consistently accurate stresses.
Extrapolation to the mid-surface intersection generally overpredicts SCFs,
but not consistently, whereas truncation at the notional weld toes would gener-
ally underpredict SCFs. In place of extrapolation, it is possible to use directly
the nodal average stresses at the mid-surface intersection. This will generally
overpredict stresses, especially on the brace side.
This last method is expected to be more sensitive to the local mesh size than
the extrapolation methods.
The general definition for stress concentration factor for any tubular joint
configuration and each type of brace loading is presented by the following
formula:

SCF = HSSR/nominal brace stress range