Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

146 Molesworth’s pocket-book Stbains on Roofs. . RULE FOR STRAINS ON IKON ROOFS. Thick lines in compression. Fine lines in tension. P = Length of principal rafter. R = Rise of roof from centre of tie-rod. T = Length of j tie-rod. L = Load on truss, including weight of framing. N = Number of bays formed by the intersection of struts and ties with, the principal rafters; in the diagram N = 10. b = Strain at end of principal rafter. F = Strain at end of tie-rod. S = LP_(N-1) 2RN Strain at p = S-—_ N-l , Q 2S ” p ^s-n=T „ Z =8-^; F_ LT(N-l) 2EN Strain at f =F--— N-l 2F N-l STRAINS ON KING AND QUEEN RODS. N-l , L ““ = 2N » = — N . 1-5L at c = ■--- N d = N