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CALCULATING WIRE ROPE LOADS
Calculating the Load of Basket Hitches & Bridles and Working Load Limits

When you’re calculating the load of basket hitches and bridles,Wire Sling Angle remember that as the horizontal angle of a sling decreases, the resultant load on each leg increases.The horizontal angle of bridles with three or more legs is measured the same way as horizontal sling angles of two-legged hitches. If a bridle is designed with different leg lengths, it may result in different horizontal angles. The load on each leg must be calculated based on the position of the slings and the location of the lift’s center of gravity.

 

Adjusting the rated capacity of a choker hitch.

Due to the body of the sling being used in the choke, there is a reduction in rated capacity. This is reflected in the choker rated capacity tables. Another reduction that must be considered is due to the “angle” of the choke (not the angle of the leg of the sling)

 

If the load is hanging free, the normal choke angle is approximately 135 degrees. When lifting and turning a load using a choker hitch, it is not uncommon to have a severe bend at the choke. When a choker hitch is used at an angle of less than 120 degrees, you must reduce the hitch’s rated capacity as shown in the chart below. You always must adjust the rated capacity of the wire rope sling whenever you use a choker hitch to shift, turn or control a load, or when the pull is against the choke in a multi-leg lift. As always, if more than one sling is used and the legs are not vertical, a further reduction in rated capacity must be made for the sling angle.

*Percent of sling’s rated capacity in a choker hitch

Warning: Choker hitches at angles greater than 135 degrees are not recommended since they are unstable. Extreme care should be taken to determine the angle of choke as accurately as possible


 

Wire Rope Working Load Limits

Numerical values published for Breaking Strength and Working Load Limit here are very specific in one point: They refer to straight, inline pull or force and are obtained under laboratory conditions. There are, however, many applications where a straight line pull is not possible or even desirable. When a tackle block system is reeved, wire rope may be bent over many sheaves; multiple leg wire rope or chain slings involve differing lifting angles; angular loads on shackles or eyebolts alter Working Load Limits of the equipment used. All these and other factors influencing the Working Load Limit must be taken into account when systems are designed and used.

The following is an example intended to demonstrate the effects of angles on the Working Load Limit.

Effects of Angles on Sling Capacities

The rated capacity of a multiple leg sling is directly affected by the angle of the sling leg with the load. As this angle decreases, the stress on each leg increases with the same load. If the sling angle is known, the capacity can be readily determined by multiplying the sling’s vertical capacity by the appropriate load angle factor from the table below.

Example: A multiple leg sling with a rated capacity of 2000 lb. will have a reduced capacity of 1000 lb. and (2000 x .500) when sling legs are at an angle of 30° with the load.

 

 

 

USING LIFTING EYEBOLTS

If a load is applied at an angle, only shoulder nut eyebolts must be used. The Working Load Limits as shown in the tables refer to straight-line pull only.

Angular loads on shoulder nut eyebolts reduce the Working Load Limit

The following table shows reduced Working Load Limit for hot galvanized shoulder nut eyebolts using 45° or 90° angles as an example.