Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

143 OF ENGINEERING FORMULÆ. Corrugated Irox. Transverse Strength. I — Unsupported length of plate in inches. t = Thickness of plate in inches. b = Breadth of plate in inches. d — Depth of corrugations in inches. W = Breaking weight distributed in tons. w = ,, ,, ,, cwts. ____ 44.6 tbd Witbd W ■——• Proportion of Pitch to depth of Corrugations. From 21 to 26 B. W. G. the pitch P is usually 3 inches. For 20 B. W. gauge and under P is usually 5 inches. 18 or 20 B. W. G. is a good gauge for ordinary roofing; all bolts, screws, or rivets must be in the ridges and not in the valleys of the cor- rugations, otherwise the roof will leak. Sheet Lead. For aprons, 5 lbs. per foot superficial. For roofs, flats, gutters, &c., 7 to 8 lbs. Hips and ridges, 6 to 8 lbs.