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American Steel Design
Section 2
2-8
F
b
= 0.66F
y
If meeting the requirements of this section of:
a) b
f
/2t
f
is less than or equal to 65/
F
y
b) b
f
/t
f
is less than or equal to 190/
F
y
c) d/t is less than or equal to 640(1-3.74(f
a
/F
y
))/
F
y
when (f
a
/F
y
)
< 0.16, or than 257/
F
y
if (f
a
/F
y
) >0.16
d) The laterally unsupported length shall not exceed 76.0b
f
/F
y
(except for pipes or tubes), nor 20,000/(dF
y
/A
f
)
e) The diameter-thickness ratio of pipes shall not exceed 3300/F
y
If for these symmetrical members, b
f
/2t
f
exceeds 65/
F
y
, but is less
than 95/
F
y
, F
b
=F
y
(0.79-0.002(b
f
/2t
f
)
F
y
)
For other symmetrical members which do not meet the above, F
b
is
calculated as the larger value computed as per AISC formulas F1-6
or F1-7 and F1-8 as applicable, but not more than 0.60F
y
. An
unstiffened member subject to axial compression or compression
due to bending is considered fully effective when the width-
thickness ratio is not greater than the following:
76.0/
F
y
, for single angles or double angles with separators.
95.0/
F
y
, for double angles in contact.
127./
F
y
, for stems of tees.
When the actual width-thickness ratio exceeds these values, the
allowable stress is governed by B5 of the AISC code.
Tension and compression for the doubly symmetric (I & H)
sections with b
f
/2t
f
less than 65/
F
y
and bent about their minor
axis, F
b
= 0.75F
y
If b
f
/2t
f
exceeds 65/
F
y
, but is less than 95/
F
y
,
F
b
= F
y
(1.075-0.005(b
f
/2t
f
)
F
y
)
For tubes, meeting the subparagraphs b and c of this Section, bent
about the minor axis, F
b
= 0.66F
y
; failing the subparagraphs b and
c but a width-thickness ratio less than 238/
F
y
, F
b
=0.6F
y
.