Assessment of Existing Structures and Repairs - Offshore Structures: Design, Construction and Maintenance - page 469

The reduction factors C mx and C my depend on the support conditions of the
member, end moments, and whether transverse loading is applied: the factors
take a value between 0.4 and 1.0.
In the case of circular section, such as pipe, these interaction equations for
circular cross-sections were adopted as presented in Chapter 3 , Equations (3.94)
and (3.95) .
When f a /F a ≤

0.15, two equations for check of buckling and strength will be
used, as discussed in Chapter 3 , Equation (3.86) .
Guidance was given on the evaluation of the reduction factor C m for differ-
ent types of jacket and deck components, and it has remained unchanged. How-
ever, in the eleventh edition (1980), allowance was made for having different
C m and F e values about the x and y axes, as in Equation (3.87) .
The interaction Equations (3.86) and (3.87) have been modified in the
LRFD version issued in 1993.

7.6.8 Combined Axial Tension and Hydrostatic Pressure
Combined axial tension and hydrostatic pressure was originally called tension
and collapse interaction when it was introduced in the sixth edition. The
terminology is now slightly misleading since the formulation also applies
to bending. In the sixth edition, the following interaction equation was
introduced:

2

A 2 ð F ys = F y Þ + ð F ys = F y Þ A + ≤ 1 : 0 (7.16)

where

f a + f b − 0 : 5 f h

A = (7.17)

0 : 6 F y

F ys was read from the design chart. It was stated that, under cyclic loads,
tension and collapse interaction need not be investigated where both of the
following apply: SF

138 Mpa.
The eleventh edition introduced an interaction equation based on the
maximum strain energy theory for biaxial loading by Beltrami and Haigh,
as in Equations (3.98), (3.99) and (3.100) . The interaction equation has
been modified in the API RP2A-LRFD introduced in 1993.
In API RP2A, the safety factors, SF, are now tabulated as in Table 7.4 ; how-
ever, it was not until the seventeenth edition that a separate safety factor for
bending was introduced.

≥ 2 for collapse alone and f a + f b ≤

7.6.9 Combined Axial Compression and Hydrostatic Pressure
Combined axial compression and hydrostatic pressure was originally called
compression and collapse. Again, when interaction was introduced in the