Page 271 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.51

CRITERIA FOR BUILDING DESIGN

CRITERIA FOR BUILDING DESIGN 5.51

µ= 0.50 for Class B surfaces (unpainted blast-cleaned steel surfaces or surfaces with Class B
coatings on blast-cleaned steel),
D u = multiplier that reflects ratio of mean installed bolt pretension to specified minimum bolt pre-
tension = 1.13
h sc = hole factor
h sc = 1.00 for standard-size holes
h sc = 0.85 for oversize and short-slotted holes
h sc = 0.70 for long-slotted holes
T b = minimum fastener tension, kips (kN) (Tables 5.8 or 5.9)
N s = number of slip planes

4. Combined Tension and Shear in Slip-Critical Type Connections. When a slip-critical connec-
tion is subjected to an applied tension that reduces the net clamping force, the available slip resis-
tance per bolt must be multiplied by the following reduction factor:
k =− T u (LRFD) (5.148a)
1
s
DT N b
u b
.
k =− 15 T a (ASD) (5.148b)
1
s
DT N b
u b
where N b = number of bolts carrying the applied tension
T a = tension force due to ASD load combinations, kips (N)
T b = minimum fastener tension, kips (kN) (see Tables 5.8 or 5.9)
T u = tension force due LRFD load combinations, kips (N)
5. Bearing Strength at Bolt Holes. Bearing strength must be checked for both bearing-type and
slip-critical connections. The available bearing strength at bolt holes for the limit state of bearing is
calculated using φ= 0.75 (LRFD) and Ω= 2.00 (ASD). The nominal bearing strength R n is deter-
mined as follows.
The bearing resistance of a connection is the sum of the bearing resistances of the individual
bolts. For a bolt in a connection with standard, oversized, and short-slotted holes independent of the
direction of loading, or a long-slotted hole with the slot parallel to the direction of the bearing force,
there are two choices.
When deformation at the bolt hole at service load is a design consideration,
(5.149a)
R n = 1.2L c tF u ≤ 2.4dtF u
When deformation at the bolt hole at service load is not a design consideration,
(5.149b)
R n = 1.5L c tF u ≤ 3.0dtF u
For a bolt in a connection with long-slotted holes with the slot perpendicular to the direction of force,
(5.150)
R n = 1.0L c tF u ≤ 2.0dtF u
The following definitions apply:
F y = specified minimum yield stress of the connected material, ksi (MPa)
F u = specified minimum tensile strength of the connected material, ksi (MPa)
L c = clear distance, in the direction of the force, between edge of hole and edge of adjacent hole
or edge of material, in (mm)
d = nominal bolt diameter, in (mm)
t = thickness of connected material, in (mm)

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