Sling Safe Working Loads

Formulas for estimating the loads for most sling configurations have been developed. These formulas are based on the safe working load of the single-vertical hitch of a particular sling. The efficiencies of the end fittings used also have to be considered when determining the capacity of the combination.

The formula used to compute the safe working load (SWL) for a bridle hitch with two, three, or four legs (fig. 13-36) is SWL (of single-vertical hitch) times H (Height) divided by L (Length) times 2 = SWL. When

Figure 13-37.-Determination of single-basket hitch sling capacity.

the sling legs are not of equal length, use the smallest H/L measurement. This formula is for a two-leg bridle hitch, but it is strongly recommended that it also be used for the three- and four-leg hitches.

NOTE: Do NOT forget it is wrong to assume that a three- or four-leg hitch can safely lift a load equal to the safe load on one leg multiplied by the number of legs.

Other formulas are as follows:

Single-basket hitch (fig. 13-37): For vertical legs, SWL = SWL (of single-vertical hitch) x 2.

For inclined legs, SWL = SWL (of single-vertical hitch) x H divided by L x 4.

Double-basket hitch (fig. 13-38): For vertical legs, SWL = SWL (of single-vertical hitch) x 4.

For inclined legs, SWL = SWL (of single-vertical hitch) x H divided by L x 4.

Single-choker hitch (fig. 13-39): For sling angles of 45 degrees or more, SWL = SWL (of single-vertical hitch) x 3/4 or .75.

Sling angles of less than 45 degrees are not _{recommended; however, if they are used,} the formula is SWL = SWL (of single-vertical hitch) x A/B.

Figure 13-38.-Determination of double-basket hitch sling capacity.

Double-choker hitch (fig. 13-40): For sling angle of 45 degrees or more, SWL = SWL (of single-vertical hitch) x 3 divided by 4 x H divided by L x 2. Sling angles of less than 45 degrees, SWL = SWL (of single-vertical hitch) x A divided by B x H divided by L x 2.

Sling Inspection

All slings must be visually inspected for obvious unsafe conditions before each use. A determination to remove slings from service requires experience and good judgment, especially when evaluating the remaining strength in a sling after allowing for normal wear. The safety of the sling depends primarily upon the remaining strength. Wire rope slings must be immediately removed from service if any of the following conditions are present: l Six randomly distributed broken wires in one _{rope lay or three broken wires in one strand in one lay}

Figure 13-39.-Determination of single-choker hitch sling

Figure 13-40.-Determination of double-choker hitch sling capacity.

l Wear or scraping on one third of the original diameter of outside individual wires . Kinking, crushing, bird caging, or any other damage resulting in distortion of the wire rope structure