THE STORAGE OF GAS
649
vertical pulis, which act parallel with the wind, the total compressive force 011 the curb may be readily calculated.
Compressive Force in Top Curb
D2P cotan. a „ „ , ~i o Ud.
8
Where D = Diameter of holder m feet.
P = Eflective pressure in Ib. per square foot.
a — Angle made by tangent with chord at base of the dorne, or the angle a may be found from the following. (Note the formulæ gives cos. a and not cotan. a direct.)
£)2 _ 4 ]>2
cos. a —------------> where E == rise of dorne in feet.
D2 + 4 R2
d = Depth of top lift in feet.
In the event of the holder being designed with vertical stays attached at top and bottom only, substitute 5 Dd for the expression 3 Dd above.
Having obtained the total compressive force it is merely necessary to design a curb of sufficient cross-sectional area to withstand this safely. A stress of 6 tons
per square inch should not be exceeded. should be remembered that the two outer the sheeting may be included in the eflective area. These plates should be butted, when the füll cross-sectional area may be considered eflective, but if lapped the shearing strength of the rivets only should be considered.
CUPS AND GRIPS
The proportions of cups and grips for telescopic holders have already been dealt with (page 627). There are two / standard types, namely, the semi-circu- i lar cup and grip, and that composed of the square channel section. The channel type is strongly to be pre-ferred. It is simply constructed, while it obviates the objectionable initial stressing which is set up in the semi-circular grip when the plate is bent to shape. Moreover, if one portion is not in perfect alignment with its counter-part, a grinding action will be set up when the two come together. This will be particularly severe when
In calculating the cross-sectional area it crown rows and the two top side rows of
Fig. 399.—Sbmt-cibcular Cup and Grip. Bent-plate Type.