Page 144 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch03.qxd 9/29/05 5:05 PM Page 3.76

CONNECTIONS

3.76 CHAPTER THREE

Additional Checks because of Change in Web Bolt Pattern
Block Shear Rupture

A nv = (7.75 – 2.5 × 1.0) (0.440 × 2) = 4.62 in 2
A gv = 7.75 × 0.440 × 2 = 6.82 in 2
A nt = (3 – 1 × 1.0) × 0.440 = 0.88 in 2
F u A nt = 65 × 0.88 = 57.2 kips
0.6F u A nv = 0.6 × 65 × 4.62 = 180 kips
0.6F y A gv = 0.6 × 50 × 6.82 = 205 kips
U bs = 1.0
φR bs = 0.75[57.2 + min(180, 205)] = 178 kips ≤ 178 kips OK
Buckling. If this were a nonbearing compression splice, the splice plates would be checked for
buckling. The following shows the method, although it is obviously not required for a tension splice.
The plates at the flange splice line are unsupported for a 4.0-in length between bolts. Check for
a load of 311/2 = 156 kips/plate. The slenderness ratio is
Kl
=
×
.
.
/
= 065 40 × 12 05 180
.
.
r
Since this value is less than 25, AISC Specification Sec. J4.4 allows the plate to be checked for yield-
ing rather than buckling. This limit state has been checked in the preceding calculations, and for the
thicker web plates as well.
3.6 MOMENT CONNECTIONS
The most commonly used moment connection is the field-welded moment connection as shown in
Fig. 3.44. This connection is in common use in all regions of the United States, where the Seismic
Design Category (SDC) is A, B, or C, and the response modification factor R is 3 or less (AISC,
“Seismic Provisions for Structural Steel Buildings”).

3.6.1 Example of Three-Way Moment Connection
The moment connection of Fig. 3.44a is termed a three-way moment connection because, in addi-
tion to the strong-axis bending, the column is subjected to minor-axis bending from both sides.
Additional views are shown in Figs. 3.44b and c. If the strong-axis connection requires stiffeners
opposite the beam flanges, there will be an interaction between the flange forces of the strong- and
weak-axis beams. If the primary function of these moment connections is to resist lateral maximum
load from wind or seismic sources, the interaction can generally be ignored because the maximum
lateral loads will act in only one direction at any one time. If the moment connections are used pri-
marily to carry gravity loads, such as would be the case when stiff floors with small deflections and
high natural frequencies are desired, there will be interaction between the weak- and strong-beam
flange forces. The calculations here assume gravity moments in both directions, although much of
the procedure is also applicable to wind or low-to-moderate seismic conditions.
The load path through this connection that is usually assumed is that the moment is carried entirely
by the flanges, and the shear entirely by the web. This load path has been verified by testing
(Huang et al., 1973) and will be the approach used here. Proceeding to the connection design, the
strong-axis beam (beam no. 1) will be designed first.

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