Manual of military engineering . inches. For field purposes C- cwts. has been laid down as the safeworking load for all cordage, but this may be increased, forgood cordage in good condition, to a maximum of 2C- c^vts. 254. The strength of wire varies greatly : as a very rough Strengthrule it may be taken that the breaking weight in pounds of wire,equals three times the weight per mile in pounds. This rule holds good for iron and hard drawn copper wire, while steel wire may be taken as about twice as strong as iron wire. The breaking strain in tons of iron wire rope is about equal Strength to t
Manual of military engineering . inches. For field purposes C- cwts. has been laid down as the safeworking load for all cordage, but this may be increased, forgood cordage in good condition, to a maximum of 2C- c^vts. 254. The strength of wire varies greatly : as a very rough Strengthrule it may be taken that the breaking weight in pounds of wire,equals three times the weight per mile in pounds. This rule holds good for iron and hard drawn copper wire, while steel wire may be taken as about twice as strong as iron wire. The breaking strain in tons of iron wire rope is about equal Strength to the square of the circumference in inches. Steel wire rope of wire rope. 102 CHAPTER XVIII.—STRENGTH OF MATERIALS, ETC. StrengUiof chain. is from 2 to 2J times as strong as iron wire rope. Wije ropecan be worked, for field service, up to half its breaking strain. 255. The following table gives the strength and weight ofordinary crane chain, obtained chiefly by experiment (ordinarycommercial iron chain is not verv reliable) :—. 256. The strength of a lashing may be taken as 4 of thenumber of returns from the object lashed, , a squarelashing with four turns has a holding power of i x 16 xstrength of rope ; in the case of a hook lashed to a spar withfour turns it is 4 x 8 x strength of rope. When using wire in lashings, multiply by | instead of 4. Timbers of 257. The following are the maximum weights, which areof bridges, brought on by the passage of troops in marching order, perlineal foot of bridge :— Infantry, in file, crowded at a check, 2J cwts. „ in fours ,, „ 5 ,, Cavalry, in single file, crowded at a check, If cwts.,, in half-sections ,, ,, 3i ,, 258. Maximum weight brought on a bridge by howitzers,guns of position, &c. :— 5-inch howitzer and ammunitionwagons, Mark II with limber. Maximumconcentrated weight in one bay = 30 cwts. 4*7-inch guns of position wdth limber, ontravelling carriage. Maximum distributedweight =85 „ C
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