Offshore Structure Platform Design - Offshore Structures: Design, Construction and Maintenance - page 141

where

f a + f b − ð 0 : 5f h Þ

A = ð SF x Þ (3.89)

F y

The term A should reflect the maximum tensile stress combination

B = f h /F hc ð SF h Þ (3.90)

where s ratio = 0.3; F y = yield strength, in ksi (MPa); f a = absolute

value of acting axial stress, in ksi (MPa); f b = absolute value of acting resultant
bending stress, in ksi (MPa); f h = absolute value of hoop compression stress, in
ksi (MPa); F hc = critical hoop stress; SF x = safety factor for axial tension; and
SF h = safety factor for hoop compression.

ν is Poisson '

Axial Compression and Hydrostatic Pressure
The following interaction equation applies if the member is under longitudinal
compression tensile stresses and hoop compressive stresses at the same time:

f a + ð 0 : 5f h Þ f b

F y ð SF b Þ ≤

ð SF x Þ + 1 : 0 (3.91)

F xc

f h
F hc ≤

SF h 1 : 0 (3.92)

Equation (3.91) should reflect the maximum compressive stress combination.
The following equation should also be satisfied when f x > 0.5F ha .

2

f x − 0 : 5F ha f h

F ha 5F ha +

≤ 1 : 0 (3.93)

F aa − 0 :

where F aa = F xe /SF x ; F ha = F he /SF h ; SF x = safety factor for axial compression;
and SF b = safety factor for bending. f x = f a + f b + (0.5 f h )andf x should reflect
the maximum compressive stress combination, where F xe ,F xc ,F he and F hc
are given by Equations (3.34), (3.73), (3.82) and (3.84) , respectively.
Note that if f b > f a + 0.5 f h , both Equation (3.88) and Equation (3.91) must
be satisfied.

Safety Factors
To compute allowable stresses, the required safety factors presented in Table 3.4
should be used with the local buckling interaction equations.