Tools › Civil and Geotechnical › Design Loads › Lifting and Rigging Loads › Example

20,000 lb load on a 4-leg bridle at about 60° with an offset centre of gravity: leg tensions by the DOE two-leg-carry rule, the load-angle factor and the required sling rating

Tool	Lifting and Rigging Loads
Source	U.S. Department of Energy (2004). Hoisting and Rigging (Formerly Hoisting and Rigging Manual). DOE-STD-1090-2004, Chapter 11: 11.3.1.1 (load angle factor example, 1,000 lb at 45°, 707 lb per leg), Figure 11-7 (load angle factors), 11.3.1.2 and Figures 11-8 / 11-9 (two legs carry the load of a 3- or 4-leg bridle), 11.3.2.d (design factor 5); Headquarters, Department of the Army (2012). Rigging Techniques, Procedures, and Applications. TM 3-34.86 / MCRP 3-17.7J, paragraph 3-32 (T = W/N × L/V, example 1,800 lb, L 8 ft, V 6 ft, 1,200 lb per leg).
Level	Professional

Problem

A 20,000 lb load with 500 lb of rigging below the hook hangs from a 4-leg wire-rope bridle attached at the corners of an 8 × 6 ft pattern; the centre of gravity sits 0.5 ft off the pattern centre along the 8 ft side and the hook is 8.66 ft above the lift points (a 5 ft half-diagonal gives 60° legs when the CG is centred). Find the angle, length and tension of every leg, the governing leg under the DOE rule that two legs carry the load, the required vertical rated capacity and breaking strength of each leg at a design factor of 5, and the margin against a sling rated 14,000 lb vertical.

Inputs to Enter

Sub-tool: sling loads and bridle; W 20,000 lb, rigging 500 lb, dynamic factor 1.0
4 legs at the corners of l_x 8 ft × l_y 6 ft, CG offset e_x 0.5 ft, e_y 0, hook height H 8.66 ft
Vertical hitch, design factor 5, sling WLL 14,000 lb (vertical)

Open the Lifting and Rigging Loads tool (loaded with this example)

Answers

Lifted weight 20,500 lb; legs 1 and 4 (far side) run r 5.408 ft, L 10.21 ft, θ 58.0°, L/H 1.179; legs 2 and 3 (near the CG) r 4.610 ft, L 9.810 ft, θ 62.0°, L/H 1.133
Two-leg carry on the governing diagonal (legs 1 and 3, CG projected onto it): vertical shares 9,430 / 11,070 lb, tensions 11,118 / 12,541 lb; the simple form W/2 × L/H with the governing leg gives 11,610 lb (the offset is what the statics add)
Alternatives shown, not used for design: three-leg carry 10,574 / 11,612 lb, equal share 5,287 / 6,532 lb
Required vertical rating per leg 12,540 lb, breaking strength 62,700 lb at DF 5; margin of the 14,000 lb sling +0.12
Checks in the test: DOE 11.3.1.1 (707 lb), Figure 11-7 rows (1/sin θ), TM 3-34.86 3-32 (1,200 lb), BNL 2,000 lb example (1,000 / 1,155 / 1,414 lb), every bridle solution against numpy.linalg

Notes

The tool's default inputs are this case; press Submit. The lift itself is illustrative (no public document prints a four-leg worked example with an offset centre of gravity); the printed examples it reproduces are the DOE, Army and BNL two-leg cases listed above, and every number comes from test_lifting_rigging_loads.php (436 checks) with the numpy script in References/Lifting-Rigging/checks/. Five rows of the DOE Figure 11-7 table (35°, 25°, 15°, 10°, 5°) differ from 1/sin θ in the third decimal and are recorded as misprints.