Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 317

The sum of all rope forces S i is equal to the force from the hanging load

Q ¼ X

z

S i

i¼1

or

Q ¼ S ð 1 þ g þ g 2 þþ g z 1 Þ:

The sum for this geometrical row is

Q ¼ S 1 g z

1 g :

ð 3 : 109 Þ

Now the efficiency of the tackle block is by definition

g tac ¼ Q

z S :

Then with ( 3.109 ) the efficiency of a tackle block with z bearing ropes is

z 1 g z

g tac ¼ 1

1 g :

ð 3 : 110 Þ

3.5.2.4 Rope Drive Efficiency

For a rope drive with n stationary sheaves and in addition a tackle block with
z bearing wire rope falls, the total rope drive efficiency is

g tot ¼ g stat g tac

or

1

z 1 g z

g tot ¼ g n

1 g :

ð 3 : 111 Þ

Example 3.15 Efficiency of a rope drive

Data:
Crane with pay load 30 t
Force from load Q = 30,000 9 9.81 = 294,000 N
Number of rope falls z = 8
Number of stationary sheaves n = 2