STRENGTH OF BOPE 35

C72 9

Working load =— =- = IT tons for occasional lifts.

C2 1 9
Working load ==— X- = — =| ton for continuous working.

O O lo

Exercise. — Find the breaking strength and the safe working loads
for occasional lifts and for continuous working of (a) 4-inch, (6) 4J-inch,
(c) 5-inch manila rope.

Breaking Working load

Ans. Strength Occasional Continuous

(a) 5Ģ tons 2f tons f tons

<*) 6f „ 2*9 „ 1J „

W S* ŧ 34 „ 1^ „

It may be required to find the size of manila rope suitable for a
given load and we then transpose the formula, for if the

working load = ---> then C2— seven times the load and C =
Example. — Find the size of the smallest manila rope suitable for
loads of (a) 3 tons and (b) \\ tons.
(a) Size of rope C=V?xload = VTx3 = V2T=4-6 inch,
Ans. For a 3-ton load use 4J-inch rope.
(6) Size of rope C=V/7xload = V^Xl*5 = VlO^ == 3J inch.
^ns. For a IJ-ton load use SJ-inch rope.
To find the number of parts of smaller rope that are equal in strength
to one part of a larger rope we simply divide the ultimate strength of
the larger rope into the ultimate strength of the smaller one.
Example. — How many parts of a 2-inch rope are equal in strength
to a 5-inch rope?
If big 0 be the size of the bigger rope its ultimate strength will be
Ca
— , and if small c be the size of the smaller rope its ultimate strength
o
c*
will be —
ultimate strength C2 3 O2 52 tfl
.% number of parts = — - - — - - -rr'===: "^x "T= TT =~Ģi ^ &*
ultimate strength 3 c2 c2 22
therefore, 6J parts of 2-inch rope is equivalent in strength to one part
of 5-inch rope,