Offshore Structure Platform Design - Offshore Structures: Design, Construction and Maintenance - page 130

Δ

from factored global actions and the associated bending stresses (P- effects)

do not need to be considered. However, when the axial member force is sub-
stantial, or when the component on which the axial force acts is very flexible,
the secondary moments due to P- Δ effects from factored global actions should

be taken into account.

Axial Tension and Bending
Tubular members subjected to combined axial tension and bending forces
should be designed to satisfy the following condition at all cross-sections
along their length:

q

f by +

γ R,b

f bz

γ R,t f t
F t +

≤ 1 : 0 (3.54)

F b

where f by is the bending stress about the member s y-axis (in-plane) due to

forces from factored actions and f bz is the bending stress about the member

'

' s

z-axis (out-of-plane) due to forces from factored actions.

Axial Compression and Bending
Tubular members subjected to combined axial compression and bending forces
should be designed to satisfy the following conditions at all cross-sections along
their length:

t

C m,y f by
1

" #

2 2

γ R,c f c

F c + γ R,b

C m,z f bz
1

+ ≤ 1 : 0 (3.55)

F b − f c /F ey − f c /F ez

and

q

f by +

γ R,b f bz

γ R,c f c
F c +

≤ 1 : 0 (3.56)

F b

where C m,y and C m,z are the moment reduction factors corresponding to the
y- and z-axes, respectively; F ey and F ez are the Euler buckling strengths corre-
sponding to the y- and z-axes respectively, in stress units, such that:

2 E
ð K y L y /r y Þ

π

F ey = (3.57)

2

2 E
ð K z L z /r z Þ

π

F ez = (3.58)

2

where K y and K z are the effective length factors for the y-andz-directions,
respectively; and L y and L z are the unbraced lengths in the y- and z-directions,
respectively.