976

MODERN STEAM PRACTICE.

to the previous strain from m to a, and the measure of h g a secondstrain on the tie from m to k, and the measure of eg the strain on the'strut ek. The strut ek then impresses a tension on kl which ismeasured b y e h, and which, together with the remaining third por-

A

Fig. 674.

Fig. 677.

Figs 674-677.—Iron Roofs. All the dark lines in compression and the light lines in tension.

A, Spans from 20 feet to 30 feet,

B, „ 3 ° >, 40 „

C, „ 40 „ 5 ° »»

V, „ 50 ,, 60 ,,

k, King rod. qq, Queen rods. rr, Rafters. ss, Struts. tt, Tie rods.

tion of the weight on the rafter, is impressed on the point /. Drawdown l i by scale equal to this pressure; draw i j parallel to the tie,then the measure of i j and j l gives the respective strains on thetie and rafter throughout.