Canadian engineer . of a square pedestal externally,with cornice, plinth and base; this will add considerablesectional area at the lowest set-off, reducing the maximumpressure^ but increasing the whole JoadI on foundations. No Tension on Inner Edge.—If tension is not to be per-mitted on the inner edge then we must find the maximum 3D^-^^wind pressure permissible by the formula / = {d \N{%B-d) being inside diameter) and p = M [d being top hRVA^ + d) diameter) 3 X i2-75=-6-7SThenZ = = 4-33456 and 8x 12-75726494-860^ X 12-75-4-33456) ?P = - = 18-54 lb. per square 61 •74X 140(12-75 + 5:75)foot as
Canadian engineer . of a square pedestal externally,with cornice, plinth and base; this will add considerablesectional area at the lowest set-off, reducing the maximumpressure^ but increasing the whole JoadI on foundations. No Tension on Inner Edge.—If tension is not to be per-mitted on the inner edge then we must find the maximum 3D^-^^wind pressure permissible by the formula / = {d \N{%B-d) being inside diameter) and p = M [d being top hRVA^ + d) diameter) 3 X i2-75=-6-7SThenZ = = 4-33456 and 8x 12-75726494-860^ X 12-75-4-33456) ?P = - = 18-54 lb. per square 61 •74X 140(12-75 + 5:75)foot as the mean effective i)r(ssui(- over the whole area, butbeing cylindrical, the equivalent normal pressure on a surface would be = lb. per square foot, or, ac- cording to Rankines coefficient, = 37 lb. per sq. ft, —It will thus be seen that, unless extraordin-ary means are taken to secure stability beyond the allow-ances that have been made in the design, a wind pressure. im^ V Fig. 10. Design Accompanying Prof. Henry Adams Paper on Tall Chimneys. varying from 38 lb. to lb. per square foot will causea maximum compression of tons per square foot and amaximum tension of tons per square foot, both beingwithin the safe limits of the material, but that if no tensionis to be allowed on the inner edge the wind pressure mustnot exceed an average of lb. per square font, or 37 lb. February 15, 1912. THE CANADIAN ENGINEER ?.>S (according- to the coefficient taken), against a normal planesurface. Prof. Unwin says (in Bridges and Roofs, p iig) : Weare in this country visited annually by gales, singularly con-stant in their maximum force, amounting to from 20 lb. to25 lb. per square foot, on a surface perpendicular to theirdirection. More rarely cyclonic storms sweep over the coun-try, during which still higher pressures are registered. Apressure of 30 lb. was registered during the Royal Charterstorm; one of 33% lb. was, obse
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