THE STORAGE OF GAS 688
between those fixed at the main upright stanchions. The construction of the top curb for a steel tank to take a spirally guided beil is shown in Fig. 423.
Thickness of Side Plates
The necessary thickness for side plates is readily calculated by considering the pressure on. the ring at a certain depth due to tlie head of water, and by treating th.e tank as an ordinary thin cylinder subjected to internal pressure.
The following is the formula employed, which may easily be deduced from flrst principles :—
P X D= 2 /te
II. o
LO I u
Where P = pressure due to water in Ib. per square inch.
D = diameter of tank in inches.
a = allowable working stress (usually 7 to 7| tons per square inch). t = thickness of plate in inches.
e = the efficiency of the vertical riveted joints. Up to 90 per cent, for large holders. For small holders it ranges from 75 to 85 per cent.
The pressure P is found as before explained, namely—
P = wd Ib. per square foot, where
w = weight of a cubic foot of water == 624 Ib.
d = depth below surface of the bottom of the plate.
Thus, to calculate the required. thickness of the bottom row for a tank 30 feet deep and 150 feet diameter we have—
P = wd — 62-4 X 30 — 1872 Ib. per square foot = 13 Ib. per square inch.
É?
1=1
II
13 X (150 X 12) 2 X 7 X 2240
X ^° = 0-83 inch.
As regards the calculation of the efficiency of riveted joints, this is a simple procedure which may be found described in full in many books on structural design. The rivets should be checked for the,ir stability in the way of resisting shearing and bearing stresses, whilst the plate at tlie joints must be sufficiently strong to preclu.de tearing, shearing or bursting through the edge. The efficiency of the jointp"
_ Least strength of joint
Strength of solid plate"
It has been shown by experiment that in many instances the ultimate resistance of tank plates is less than the stress that would be necessary to overcome the friction at the j oints, and that the friction is so great that within. the limits of working stress there is neither shear in. the rivet nor bearing stress against the shank. Such a