Page 222 - Pressure Vessel Design Manual

200 Pressure Vessel Design Manual
Notes 6. The value of K represents the location of the neutral
axis between the anchor bolts in tension and the con-
1. Base plate thickness: crete in compression. A preliminary value of K is esti-

0 If t 5 % in., use Type 1. mated based on a ratio of the “allowable” stresses of the
0 If % in. < t 5 % in., use Type 2. anchor bolts and concrete. From this preliminary value,
a If t > in., use Type 3 or 4. anchor bolt sizes and numbers are determined and
actual stresses computed. Using these actual stresses,
2. To reduce sizes of anchor bolts:
the location of the neutral axis is found and thus an
a Increase number of anchor bolts. actual corresponding K value. A comparison of these
a Use higher-strength bolts. K values tells the designer whether the location of the
a Increase width of base plate. neutral axis he assumed for selection of anchor bolts
was accurate. In successive trials, vary the anchor bolt
3. Number of anchor bolts should always be a multiple of sizes and quantity and width of base plate to obtain an
4. If more anchor bolts are required than spacing optimum design. At each trial a new K is estimated and
allows, the skirt may be angled to provide a larger
bolt circle or bolts may be used inside and outside of calculations repeated until the estimated K and actual
the skirt. Arc spacing should be kept to a minimum if K are approximately equal. This indicates both a
possible. balanced design and accurate calculations.
4. The base plate is not made thinner by the addition of a 7. The maximum compressive stress between base plate
compression ring. tt, would be the same as required for and the concrete occurs at the outer periphery of the
chair-type design. Use a compression ring to reduce base plate.
induced stresses in the skirt or for ease of fabrication 8. For heavy-wall vessels, it is advantageous to have the
when chairs become too close. center lines of the skirt and shell coincide if possible.
5. Dimension “a” should be kept to a minimum to reduce For average applications, the O.D. of the vessel and
induced stresses in the skirt. This will provide a more O.D. of the skirt should be the same.
economical design for base plate, chairs, and anchor 9. Skirt thickness should be a minimum of R/200.
bolts.

PROCEDURE 3-15

DESIGN OF BASE DETAILS FOR VERTICAL VESSELS #2

f, =tension force per bolt, lb
Notation f, =bearing pressure on foundation, psi
Mb = overturning moment at base, ft-lb
E =joint efficiency MT = overturning moment at tangent line, ft-lb
El = modulus of elasticity at design temperature, psi
A,, = cross-sectional area of bolts, in. 2
d =diameter of boIt circle, in.
Wb =weight of vessel at base, Ib Allowable Stresses
WT =weight of vessel at tangent line, lb
w =width of base plate, in.
S = code allowable stress, tension, psi *0.6Fy =
N =number of anchor bolts FT = lesser of 1.33s =
FL = allowable bearing pressure, concrete, psi
Fy = minimum specified yield stress, skirt, psi
F, = allowable stress, anchor bolts, psi
fLT = axid1 load, tension, lb/in.-circumference 0.333Fy =
fLc = axial load, compression, lb/in.-circumference 1.33 Factor B =
FT = allowable stress, tension, skirt, psi F, = lesser of
F, = allowable stress, compression, skirt, psi
Fb = allowable stress, bending, psi 1.33s =