TUBE DRILLING MACHINE ON DRILL ROAD.
_Figs._72_to_74,_Page_36.png)
strength if the change occurs frequently, and 221⁄2 tons if occurring rarely.
For stresses alternately tensile and compressive, the ultimate stress to be 10 tons if frequent and 15 tons if seldom, one-third of the ultimate strength to be considered the working stress.
Rivet-steel to have an ultimate strength of 27 tons per square inch, with 30 per cent, of elongation, and shearing resistance to be from 22 tons to 24 tons per square inch.
Cast steel to have an ultimate tensile strength of 30 tons, with 8 to 10 per cent. elongation.
For tension members the sectional area of the rivets in the joints to be 11⁄2 times the useful section of the boom.
For compression members the area of rivets in butt-joints to be half the useful section of the member.
The original estimate gave the quantity of steel required for the Cantilever Bridge (not including approach viaduct spans) as 42,000 tons. Of this quantity the Landore Works near Swansea in South Wales, of Messrs. Siemens, supplied 12,000 tons, and the Steel Company of Scotland, from their
