Civil Engineering Reference
In-Depth Information
TABLE 3.2
Effective Length and Moment Reduction Factors for Member
Strength Checking
Structural Component
K m
Topside legs
Braced
1.0
0.85
K
b
Portal (unbraced)
0.85
Structure legs and piling
Grouted composite section
1.0
C
m = 1.0
−
0.4
•
(
f
c
/
F
e
), or 0.85,
whichever is less
Ungrouted jacket legs
1.0
C
m = 1.0
−
0.4
•
(
f
c
/
F
e
), or 0.85,
whichever is less
Ungrouted piling between shim points 1.0
C
m = 0.6
−
0.4
•
M
1/
M
2
M
1/
M
2
a
or
C
m= 1.0
Structure brace members
C
m= 0.6
−
0.4
•
−
0.4
•
(
f
c
/
F
e
), or 0.85, whichever is less
Primary diagonals and horizontals
0.7
K braces
c
0.7
X braces
0.7
C
m = 1.0
−
0.4
•
(
f
c
/
F
e
), or 0.85,
whichever is less
Longer segment length
c
0.8
Full length
d
0.7
Secondary horizontals
0.7
a
M
1
/M
2
is the ratio of smaller to larger moments at the ends of the unfaced portion of the member in
the plane of bending under consideration. M
1
/M
2
is positive when the member is bent in reverse
curvature, negative when bent in single curvature. F
e
=F
ey
or F
ez
as appropriate.
b
Use effective length alignment chart as in
Figure 3.28
.
c
For either in-plane or out-of-plane effective lengths, at least one pair of members framing into a K or X
joint should be in tension, if the joint is not braced out of plane.
d
When all members are in compression and the joint is not braced out of plane.
3.6.2 Cylinder Member Strength Calculation
The design of the cylinder member in accordance with API is based on AISC
allowable stress design.
Axial Tension
The allowable tensile stress, F
t
, for cylindrical members subjected to axial ten-
sile loads should be determined from:
F
t
=
0
:
6F
y
(3.70)
where F
y
= yield strength, in ksi (MPa).
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