Page 247 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.27

CRITERIA FOR BUILDING DESIGN

CRITERIA FOR BUILDING DESIGN 5.27

where (b/t) st = stiffener width–thickness ratio
F yst = specified yield stress of the stiffener material, ksi (MPa)
C v = coefficient defined in Art. 5.6.1
D s = 1.0 for stiffeners in pairs
= 1.8 for single-angle stiffeners
= 2.4 for single-plate stiffeners
V r = required shear strength at the location of the stiffener, kips (N)
V c = available shear strength; φV n (LRFD) or V n /Ω (ASD) with V n as given by Eq. (5.95) or
(5.96), as applicable

5.6.3 Shear Strength of Other Members
For single angles, calculate the nominal shear strength V n using Eq. (5.88) with C v = 1.0 and A w = bt,
where b = width of the leg resisting the shear force, in (mm). Also, k v = 1.2.
For rectangular HSS and box members, calculate V n from the equations in Art. 5.6.2, with
A w = 2ht, where h is the width resisting the shear force, taken as the clear distance between flanges
less the inside corner radii; t is the wall thickness, and k v = 5. If the corner radius of a hollow struc-
tural section is not known, h may be taken as the corresponding outside dimension minus three times
the wall thickness.
For round HSS calculate V n as follows:
FA
V = cr g (5.99)
n
2
where A g is the gross cross-section area. The critical buckling stress F cr is the larger of the following
two equations, but also must not exceed 0.6F y :

.
F = 160 E (5.100)
cr
/
LD D t / ) 34
/(
v
.
F = 078 E (5.101)
cr
/
(/ 32
Dt)
3
2
where A g = gross area of section based on design wall thickness, in (mm )
D = outside diameter, in (mm)
L v = distance from maximum to zero shear force, in (mm)
t = design wall thickness, in (mm)
For singly and doubly symmetric shapes loaded in the weak axis without torsion, calculate V n
for each shear-resisting element using Eq. (5.88), and the limits in Eqs. (5.89) to (5.91), with A w =
b f t f (flange width × flange thickness) and k v = 1.2. Note that for ASTM A6 W, S, M, and HP shapes,
when F y ≤ 50 ksi (345 MPa), C v = 1.0.
5.7 DESIGN FOR COMBINED FORCES AND TORSION
Where a member is subjected to axial force and flexure concurrently, and possibly torsion as well,
interaction equations are used to consider the combined effects. Such equations involve calcula-
tion of ratios of required to available strength. This article addresses members subjected to axial
force and flexure about one or both axes, with or without torsion, and members subject to torsion
only. The AISC Specification gives these equations, but also provides alternative methods for
some cases.

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