Recording the allowable stresses and modular ra-
tio by using the ACI Code, we get p = 750 lb/in
2
(5170 kPa) and n = 9. From the AISC Specification,
fs = 14,000 lb/in
2
(96.5 MPa); the allowable bending
stress in the plate is 27,000 lb/in
2
(186.1 MPa).
- Construct the stress
and force diagrams
These are shown in Fig. 13. Then^/« = 14/9 = 1.555
kips/in
2
(10.7 MPa); kd = 23(0.750/2.305) = 7.48 in
(190.0 mm); Jd = 23 - 7.48/3 = 20.51 in (521.0 mm). - Design the base plate
Thus, C = Y 2 (IAS)(OJSOB) = 2.8055. Take mo-
ments with respect to the anchor bolt, or SAf =
30(10) + 1100 - 2.8055(20.51) = O; B = 24.3 in
(617.2mm).
Assume that the critical bending stress in the
base plate occurs at the face of the column. Compute
the bending moment at the face for a 1-in (25.4-mm)
width of plate. Referring to Fig. 13c, we have/>' =
0.750(1.48/7.48) = 0.148 kips/in^2 (1020.3 kPa); M =
(6^2 /6)(0.148 + 2 x 0.750) = 9.89 in-kips (1.12
kN-m); t^2 -6M/21 = 2.20 in^2 (14.19 cm^2 ); t= 1.48 in
(37.6 mm). Make the base plate 25 in (635 mm)
wide and I
1
A in (38.1 mm) thick. - Design the anchor bolts
From the calculation in step 3,C = 2.8055 =
2.805(24.3) - 68.2 kips (303.4 kN); T= 68.2 - 30 =
38.2 kips (169.9 kN); A 5 = 38.2/14 - 2.73 in^2 (17.61
cm
2
). Refer to the AISC Manual. Use 2%-in (57.2- (c) Stresses
mm) anchor bolts, one on each side of the flange.
Then A 3 = 3.02 in^2 (19.48 cm^2 ). FIGURE 12. Anchor-bolt de- - Design the anchorage for the bolts
tails
(
fl
)
plan
' (*) elevation;
The bolts are held by angles welded to the column ^)stresses-
flange, as shown in Fig. 12 and in the AISC Manual.
Use^1 X 2 -In (12.7-mm) angles 12 in (304.8 mm) long.
Each line of weld resists a force of^1 AT. Refer to Fig.
13 d and compute the unit force F at the extremity of
the weld. Thus, M= 19.1(3) = 57.3 in-kips (6.47 kN-m); Sx = (V6)(12)^2 24 in^2 (154.8 cm^2 );
Fx = 57.3/24 - 2.39 kips/lin in (0.43 kN/mm); F = 19.1/12 = 1.59 kips/lin in (0.29
kN/mm); F = (2.39^2 + 1.59^2 )^05 = 2.87 kips/lin in (0.52 kN/mm). Use a^5 Xi 6 -in (4.8-mm)
fillet weld of E60 electrodes, which has a capacity of 3 kips/lin in (0.54 kN/mm).
GRILLAGE SUPPORT FOR COLUMN
A steel column in the form of a W14 x 320 reinforced with two 20 x \
l
/2 in (508 x 38.1
mm) cover plates carries a load of 2790 kips (12,410 kN). Design the grillage under this
column, using an allowable bearing stress of 750 lb/in
2
(5170.5 kPa) on the concrete. The
space between the beams will be filled with concrete.(b) Elevation(a) Plan