Page 235 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.15

CRITERIA FOR BUILDING DESIGN

CRITERIA FOR BUILDING DESIGN 5.15

When 0 ≤ (L/r x ) ≤ 80,

KL L
+
= 72 0 75 (5.33)
.
r r
x
When (L/r x ) > 80,
KL L
+
.
= 32 1 25 ≤ 200 (5.34)
r r x
For unequal-leg angles with leg length ratios less than 1.7 connected through the shorter leg, the
2
KL/r from Eqs. (5.33) and (5.34) should be increased by adding 4[(b l /b s ) − 1], but KL/r should not
be less than 0.95L/r z .
For equal-leg angles or unequal-leg angles connected through the longer leg that are web members
of box or space trusses with adjacent web members attached to the same side of the gusset plate or chord:
When 0 ≤ (L/r x ) ≤ 75,
KL L
+
.
= 60 0 8 (5.35)
r r x
When (L/r x ) > 75,
KL L
= 45 + ≤ 200 (5.36)
r r x
For unequal-leg angles with leg length ratios less than 1.7, connected through the shorter leg, the
2
KL/r from Eqs. (5.35) and (5.36) should be increased by adding 6[(b l /b s ) − 1], but KL/r should not
be less than 0.82L/r z .
The following definitions apply:
L = length of member between work points at truss chord centerlines, in (mm)
r z = radius of gyration about minor axis, in (mm)
r x = radius of gyration about axis parallel to connected leg, in (mm)
b l = longer leg of angle, in (mm)
b s = shorter leg of angle, in (mm)

5.4.4 Compressive Strength of Built-up Members

The compressive strength of built-up members comprised of two or more shapes interconnected by
stitch bolts or welds should be determined from Eqs. (5.19) to (5.22), but with KL/r replaced by a
modified column slenderness ratio (KL/r) m determined as follows.
For intermediate connectors that are snug-tight bolted,

 KL  =  KL  2  a  2 (5.37)
 r  m  r  +  
r  
i
For intermediate connectors that are welded or fully tensioned bolted,

 KL  =  KL  2 α 2  a  2 (5.38)
 r  m  r  o + 082. 1 ( + α 2  r  ) ib  

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.