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Section 2
2-9
2.3.5 Combined Compression and Bending
Members subjected to both axial compression and bending stresses
are proportioned to satisfy AISC formula H1-1 and H1-2 when
f
a
/F
a
is greater than 0.15, otherwise formula H1-3 is used. It
should be noted that during code checking or member selection, if
f
a
/F
a
exceeds unity, the program does not compute the second and
third part of the formula H1-1, because this would result in a
misleadingly liberal ratio. The value of the coefficient C
m
is taken
as 0.85 for sidesway and 0.6 - 0.4 (M1/M2), but not less than 0.4
for no sidesway.
2.3.6 Singly Symmetric Sections
For double angles and Tees which have only one axis of symmetry,
the KL/r ratio about the local Y-Y axis is determined using the
clauses specified on page 3-53 of the AISC ASD 9
th
ed. Manual.
2.3.7 Torsion per Publication T114
The AISC 89 code of specifications for steel design currently does
not have any provisions specifically meant for design of sections
for Torsion. However, AISC has published a separate document
called “Torsional Analysis of Steel Members” which provides
guidelines on transforming torsional moments into normal stresses
and shear stresses which can then be incorporated into the
interaction equations explained in Chapter H of the AISC 89 code.
The guidelines of the publication have been incorporated into the
AISC-89 steel design modules of STAAD.
To consider stresses due to torsion in the code checking or member
selection procedure, specify the parameter TORSION with a value
of 1.0. See Table 2.1 for more details.