Page 251 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.31

CRITERIA FOR BUILDING DESIGN

CRITERIA FOR BUILDING DESIGN 5.31

For 3 07 EF < / h t ≤ 260,
/
.
y
0 458π 2 E
.
F = (5.113)
cr
ht)
(/ 2
5.7.5 Round and Rectangular HSS under Torsion and Other Forces
If the required torsional strength T r does not exceed 20% of the available torsional resistance T c , check
interaction using Art. 5.7.1, neglecting torsion. Otherwise, the interaction of forces is limited by
 P M   V T  2
 r + r  +  r + r  ≤1.0 (5.114)
 P c M   V c T 
c
c
The following definitions apply for LRFD design, using LRFD load combinations:
P r = required axial strength, kips (N)
P c =φP n = design tensile or compressive strength, kips (N)
M r = required flexural strength, kip⋅in (N⋅mm)
M c =φ b M n = design flexural strength, kip⋅in (N⋅mm)
V r = required shear strength, kips (N)
V c =φ v V n = design shear strength, kips (N)
T r = required torsional strength, kip⋅in (N⋅mm)
T c =φ T T n = design torsional strength, kip⋅in (N⋅mm)

The following definitions apply for ASD design, using ASD load combinations:
P r = required axial strength, kips (N)
P c = P n /Ω= allowable tensile or compressive strength, kips (N)
M r = required flexural strength, kip⋅in (N⋅mm)
M c = M n /Ω b = allowable flexural strength, kip⋅in (N⋅mm)
V r = required shear strength, kips (N)
V c = V n /Ω v = allowable shear strength, kips (N)
T r = required torsional strength, kip⋅in (N⋅mm)
T c = T n /Ω T = allowable torsional strength, kip⋅in (N⋅mm)

5.7.6 Members Other Than HSS under Torsion and Other Forces

Members other than HSS under torsion generally develop both normal stress and shear stress. (See
“Torsional Analysis of Structural Steel Members,” Design Guide No. 9, AISC, 1997). The design tor-
sional strength φF n and the allowable torsional strength F n /Ω for non-HSS members is taken as the
lowest value obtained for the limit states of yielding (under normal stress), shear yielding, and buck-
ling. Use Eqs. (5.115) to (5.117) to determine F n with φ T = 0.90 (LRFD) and Ω T = 1.67 (ASD).
For the limit state of yielding,
(5.115)
F n = F y
For the limit state of shear yielding,
(5.116)
F n = 0.6F y

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