Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

3G2 moleswobth’s pocket-cook Stbains on Telegraph Wire. WITH BÜPPOKTS AT VNEQVAL LEVELS—continued. p = The parameter. = Twice the working strain of the wire. _ L1— ap , X 2L, ' ■ La + a p 2 al '' TO FIND THE FACTOIiS OF THE BACK SPAN. S rt Length of main span in yards. s = „ 11 back „ d = Dip of back span in feet. n =■ Proportion of weight per mile of back span wire to that of main span wire. r — Proportion of dip in feet per 100 yards at which the main span wire is calculated. WIND PRESSURE. f = Pressure of wind in lbs. per square foot. W = Weight of wire in lbs. per mile. L = Length of curve in feet. F = Total pressure of wind on any length L in lbs. b = Diameter of wire in inches. fjj __ fLb F = 2117 16 W “78" STRAIN ON STAYS. T = Strain on the insulator. 0 == Augie the stay makes with the ground. Strain on the stay = ------ • • cos. 0