Page 270 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.50

CRITERIA FOR BUILDING DESIGN

5.50 CHAPTER FIVE

where F n = nominal tensile strength F nt or shear strength F nv (Table 5.16)
A b = nominal unthreaded body area of bolt or threaded part (for upset rods, see footnote [d],
2
2
Table 5.16), in (mm )
The required tensile strength must include any tension resulting from prying action produced by
deformation of the connected parts.

2. Combined Tension and Shear in Bearing-Type Connections. For a bolt subjected to combined
tension and shear, the available tensile strength is determined for the limit states of tension rupture
and shear rupture:
(5.144)
R n = F nt ′ A b
φ= 0.75 (LRFD) Ω= 2.00 (ASD)
where F nt ′ is the nominal tensile strength per unit area modified to include the effects of shear, ksi
(MPa), as defined by the following equations.
For LRFD,

F ′ = 13. F − F nt f ≤ F (5.145)
nt
nt
φ F nv v nt
For ASD,
Ω F
F nt ′ = 13. F nt − nt f v ≤ F nt (5.146)
F nv

where F nt = nominal tensile stress (Table 5.16), ksi (MPa)
F nv = nominal shear stress (Table 5.16), ksi (MPa)
f v = required shear stress, ksi (MPa)
Also, the available shear stress of the fastener must equal or exceed the required shear stress f v .
Note that when the required stress in either shear or tension is less than or equal to 20% of the cor-
responding available strength per unit area, the effects of combined stress need not be investigated.
3. High-Strength Bolts in Slip-Critical Connections. High-strength bolts in slip-critical connec-
tions may be designed for the limit state of slip at either a serviceability limit state or at the required
strength limit state. The connection must also be checked for shear strength and bearing strength.
The AISC Specification indicates that, unless otherwise designated by the engineer of record, con-
nections with standard holes or slots transverse to the direction of the load should be designed for
slip at a serviceability limit state, and connections with oversized holes or slots parallel to the direc-
tion of the load should be designed for slip at the required strength. Generally, connections with stan-
dard holes or slots transverse to the direction of the load would only be designed for slip at the
required strength for special cases where deformations due to slip could cause a structural failure as
a result of changes in structure geometry.
The design slip resistance φR n and the allowable slip resistance R n /Ω is determined from the fol-
lowing equation for the limit state of slip:
(5.147)
R n =µD u h sc T b N s
For connections designed for slip at a serviceability limit state, φ= 1.00 and Ω= 1.50. For connec-
tions designed for slip at the required strength limit state, φ= 0.85 and Ω= 1.76.
The following definitions apply:
µ= mean slip coefficient
µ= 0.35 for Class A surfaces (unpainted clean mill scale on steel surfaces, surfaces with Class A
coatings on blast-cleaned steel, and hot-dipped galvanized and roughened surfaces)

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