Page 116 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch03.qxd 9/29/05 5:05 PM Page 3.48

CONNECTIONS

3.48 CHAPTER THREE

L
L

Single brace to gusset Double brace to gusset
along beam span along beam span
K = 1.2 K = 0.65 with one brace in tension
and one brace in compression
K = 1.2 with both braces in compression
L
L

Brace at beam-column X-bracing intersection
connection (brace with kicker sim.)
K = 0.5 K = 2.0

L

L

Flange plate moment Strut connection
connection K = 1.2
K = 0.65
FIGURE 3.29 K factors and buckling lengths for plates in compression.

In many cases, the full width of the plate cannot be considered effective to resist buckling.
Therefore, the Whitmore section illustrated in Fig. 3.30 is taken as the effective width of the plate. The
Whitmore section is assumed to extend along the length of the connection at a 30° angle to either side.

Plates in Bending. The strength of plates in bending can also be governed by buckling. Again, the
boundary conditions are important in determining behavior. Typically, plates in bending are assumed
to be free along one unloaded edge and simply supported along the other. The loaded edges are both
usually assumed to be simply supported. This is the approach used in the AISC Manual. The critical
buckling strength in bending is defined (Muir and Thornton, 2004) as

φF cr = 0.9F y Q (3.51)
where Q = 1 for λ≤ 0.7
= 1.34 – 0.486λ for 0.7 <λ≤ 1.41
2
= 1.30/λ for λ> 1.41

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