Offshore Structure Platform Design - Offshore Structures: Design, Construction and Maintenance - page 149

TABLE 3.6 Values of F 1 , F 2 and F 3

Joint Type F 1 F 2 F 3

T/Y joints under brace axial loading 0.3 0 0.8

K joints under brace axial loading 0.2 0.2 0.3

X joints under brace axial loading a

β ≤ 0.9 0.2 0 0.5

β = 1.0 − 0.2 0 0.2

All joints under brace moment loading 0.2 0 0.4

a Linearly interpolated values between

β = 0.9 and β = 1.0 for X joints under brace axial loading.

of the chord. [Where increase is applicable, FS = 1.20 in Equations (3.97) and
(3.98) .]
Table 3.6 presents the coefficients F 1 , F 2 and F 3 , which depend on joint and
load type.
The average of the chord loads and bending moments on either side of the
brace intersection should be used in Equations (3.97) and (3.98) .Chordaxial
load is positive in tension, and chord in-plane bending moment is positive
when it produces compression on the joint footprint. The chord thickness at
the joint should be used in the above calculations.

Joints with Thickened Cans
For simple, axially loaded Y and X joints where a thickened joint can is speci-
fied, the joint allowable capacity may be calculated as:

2

P a = ½ r + ð 1 − r Þð T n /T c Þ ð P a Þ c (3.99)

where (P a ) c = P a from Equation (3.94) based on chord can geometric and
material properties, including Q f calculated with respect to chord can; T n =
nominal chord member thickness; T c = chord can thickness; r = L c /(2.5D)
for joints with

0.9;
and L c = effective total length as in Figure 3.30 ,thatr cannot have a value
greater than unity.
Alternatively, an approximate closed-ring analysis will be used in the calcula-
tion, including plastic analysis with a suitable factor of safety that covers the
approximation in the calculation and using an effective chord length up to
1.25D, where D is the chord diameter, on either side of the line of action of
the branch loads at the chord face, but not more than the actual distance to the
end of the joint can. The finite element method can be used in case of more com-
plex joints. For multiple branches in the same plane, dominantly loaded in the

β ≤ 0.9 and r =(4 β − 3)L c /(1.5D) for joints with β >