Civil Engineering Reference
In-Depth Information
K and Cm values can be obtained from
Table (3.3)
for different structural
members, where
s
2
2
E
F
y
π
C
c
=
E is Young
s modulus of elasticity, in ksi (MPa); K is the effective length factor;
l is the unbraced length, in m (in); and r is the radius of gyration, in m (in).
'
TABLE 3.3 K and Cm Values Based on API RP2A
Effective
Length
Factor K
Structure element
Reduction Factor Cm
Superstructure legs
Braced
1.0
0.85
K
a
Portal (unbraced)
0.85
Jacket legs and piling
Grouted composite section
1.0
Min of {1
−
0.4(
f
a
/
F
e
)} or 0.85
Ungrouted jacket legs
1.0
Min of {1
−
0.4(
f
a
/
F
e
)} or 0.85
Ungrouted piling between
shim points
1.0
0.6
−
0.4(
M
1/
M
2), 0.4
<
C
m
<
0.85
Deck truss web members
0.6
−
0.4(
M
1/
M
2), 0.4
<
C
m
<
0.85
In-plane action
0.8
0.6
−
0.4(
M
1/
M
2), 0.4
<
C
m
<
0.85 or 0.85
Out-of-plane action
1.0
0.85
Jacket braces
0.6
−
0.4(
M
1/
M
2), 0.4
<
C
m
<
0.85 or Min
of {1
−
0.4(
f
a
/
F
e
)} or 0.85
Face-to-face length of main
diagonals
0.8
Face-of-leg to centerline of
joint length of K braces
b
0.8
Min of {1
−
0.4(
f
a
/
F
e
)} or 0.85
Longer segment length of X
braces
b
0.9
Min of {1
−
0.4(
f
a
/F
e
)} or 0.85
Secondary horizontals
0.7
Min of {1
−
0.4(
f
a
/
F
e
)} or 0.85
Deck truss chord members
1.0
0.85 or 6
−
0.4(
M
1/
M
2), 0.4
<
C
m
<
0.85
or Min of {1
−
0.4(
f
a
/
F
e
)} or 0.85
a
As in
Figure 3.28
.
b
At least one pair of members framing into a joint must be in tension if the joint is not braced out of plane.
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