628 MODERN GASWORKS PRACTICE
in all cases conform to a segment of a sphere. Normally, the rise will lie between Ts Tö t^ie diameter (though seldom -j-V), a greater pitch being given when no trussing is employed. The cubic capacity of the crown space may be found aa foliows :—
/ 3 D2\
Volume (in cubic feet) = 0-5236 K ^R2+ —J
Where R = Rise of crown in feet, and D == Diameter of holder in feet (top lift).
Proportions of Lifts
The ratio of the deptli of a lift to its diameter varies to some considerable extent, but it has been laid down by Cripps as a working principle that the depth of the lift must never be less than one-seventh of its diameter, otherwise tilting is extremely likely to occur. In ordinary practice the proportion varies from one-fourth. to one-fifth of the diameter.
THE GUIDE-FRAMING OF GASHOLDERS
The author takes this opportunity of pointing out that the knowledge we have of the stresses and strains in gasholder structures at the present day is almost solely built up from the theories expounded by the late Sir Benjamin Baker and by Mr. F. Southwell Cripps. The latter has published an eminently practical and scientific treatise—now unhappily out of print—which has for long been and still remains the standard work of reference on the subject. The treatment adopted by the author in the following pages—so far as the stresses in the guide-framing and top curb are concerned—is, for the most part, a reiteration of the deductions and methods of Mr. Cripps, as set forth in his work entitled, “ The Guide-framing of Gasholders, and other papers chiefly relating to the strains in structures connected with Gas-Works.”
The stresses occurring in the guide-framing of a gasholder are occasioned by pres-
sure of wind and snow. The weight of the members themselves will, however, give rise to certain loading, and this efiect must not altogether be neglected. In calcula-tions of the kind it is customary to assume a wind pressure equal to a maximum of 32 1b. per square foot, but owing to the surface on which the pressure is received