Page 132 - Handbook of Structural Steel Connection Design and Details

Design of Connections for Axial, Moment, and Shear Forces

Design of Connections for Axial, Moment, and Shear Forces 117

Thus, T 0.75(1.8 50) 0.780 0.523 27.5 kips and F 2
fy
27.5 55.0 kips.
The flange force for design of the splice is thus

f 5 F 1 max5F , F 6 5 98.2 1 max5110, 55.06 5 208 kips
f
f t
f y
f x
Suppose that M 3/8 M . Let M 1500 kips-in, say, 1 7.5/14.565
f py f
1.515 and check M 1500 kips in 3/8 M (1.515) 1410
2
f py
3236 kips in, so proceeding
1 1500
ε 5 3 14.565 3 1.515c1 2 1 2 d 5 1.476 in
4 B 3236
T 0.75 (1.8 50) 0.780 1.476 77.5 kips and F 2 T 155
fy
kips, which is still less than the maximum possible value of F =
fy
1500/7.5 3 2 5 400 kips
Returning to the splice design example, the splice will be designed for
a load of 208 kips. Since the columns are of different depths, fill plates
1
1
will be needed. The theoretical fill thickness is (15 / 14 / )/2 11/16
2 8
1
in, but for ease of erection, the AISC suggests subtracting either / or
8
3 / in, whichever results in / -in multiples of fill thickness. Thus, use
1
16 8
actual fills 11/16 3/16 1/2 in thick. Since this splice is a bearing
splice, either the fills must be developed, or the shear strength of the
bolts must be reduced. It is usually more economical to do the latter in
accordance with AISC Specification Section J6 when the total filler
3
thickness is not more than / in. Using Section J6, the bolt shear design
4
strength is
r 44.2 [1 0.4(0.5 0.25)] 39.8 kips
v
The number of bolts required is 208/39.8 5.23 or 6 bolts. The choice of
six bolts here may have to be adjusted for bearing/tearout as will be seen
later. By contrast, if the fillers were developed, the number of bolts required
would be 208 [1 0.5/(0.5 0.780)]/44.2 6.54 or 8 bolts. By reducing
the bolt shear strength instead of developing the fills, [(8 6)/8]100 25%
fewer bolts are required for this splice. Next, the splice plates are designed.
These plates will be approximately as wide as the narrower column flange.
Since the W14 99 has a flange width of 14-5/8 in., use a plate 14-1/2 in.
wide. The following limit states are checked:
1. Gross area: The required plate thickness based on gross area is t
p
208/(0.9 36 14.5) 0.44 in. Use a 1/2-in plate so far.
2
2. Net area: The net area is A (14.5 2 1.125) 6.5 6.125 in , but
n
2
this cannot exceed 0.85 of the gross area or 0.85 14.5 0.5 6.16 in .

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