Guide to Stability Design Criteria for Metal Structures下.pdf

510 STABILITY OF ANGLE MEMBERS
design of hot-rolled, single-angle members with equal and unequal legs in tension,
shear, compression, flexure, bined stresses.
The 1993 specification for single angles (AISC, 1993) addressed general flexural
behavior as well as axial load capacity. Using the LRFD procedure for axially
loaded angle members, only flexural buckling is considered. While the specification
mends the use of the AISC LRFD interaction formula to address the effects of
biaxial bending, it indicates that the terms should reflect the stresses at a particular
location on the cross section.
In 2000, the single-angle specification was updated (AISC, 2000). The permitted
shape factor for flexure was made less conservative and specific local buckling lim-
its for flexure were introduced. For axially loaded single-angle members, strength
limit states were based only on flexural buckling because flexural–torsional buck-
ling was deemed not critical for hot-rolled angles.
Five years later, the single-angle provisions were incorporated into the Specifica-
tion for Structural Steel Buildings (AISC, 2005). The provisions remain unchanged
for the general determination of the axial and flexural capacity of single angles,
except for the modification of the interaction expression intended for single-angle
members. An empirical effective-length procedure, however, was introduced for
the design of single-angle (equal-leg and some unequal-leg) struts in which one
leg at each end is attached to a truss chord. The procedure covers two conditions:
1. Box trusses in which the chords are well restrained torsionally:
⎧
⎪ L L
⎨⎪ 60 + for 0 ≤≤ 75 ()
KL = rx rx
r ⎪ L L
⎩ 45 + ≤ 200 for > 75 ()
rx rx
(Note that these equations are equivalent to Eqs. and , respec-
tively, for equal-leg angles in transmission towers.)
2. Planar trusses in which the chords are considered to be less torsionally
restrained:
⎧
⎪ L L
⎨⎪ 72 + for