Spreader Beam Minimum Top-Point Height
The minimum top-point height so the top-sling tension stays within the sling WLL.
Example
You enter
- Total load (lb) 10000
- Bar length, pick to pick (ft) 10
- Top sling WLL, each (lb) 6000
You get
- Minimum top-point height 7.54 ft
- Sling angle at that height 56.44
Checked against published worked examples from: ASME BTH-1 / B30.20 (solved for the height).
Details, formula, and sources
ScopeSince a taller rig makes a steeper sling that pulls less. angle = asin( load / (2 x WLL) ), then top = (bar/2) x tan(angle). A 10,000 lb load on a 10 ft bar with 6,000 lb slings needs at least 7.54 ft of top height. Answers 'how much headroom do I need' instead of the tension from a set height. The WLL must exceed half the load. ASME BTH-1 / B30.20 and the rating plate govern.
Formula or tableangle_min = asin( load / (2 x sling_wll) ); min_top_height = (bar_length/2) x tan(angle_min); bar_compression = (load/2) / tan(angle_min). The inverse of top_sling_tension = (load/2)/sin(angle) with angle = atan(top/(bar/2)); solvable only when sling_wll > load/2.
Source and editionASME BTH-1 (Design of Below-the-Hook Lifting Devices) and ASME B30.20 by name, solved for the top-point height; first-principles statics.
Free accessASME BTH-1 and B30.20 are published consensus standards. The statics are public.
What governsEstimate. Head rigger and manufacturer working-load-limit charts govern. Inspect every piece of hardware before the show.
API field namesload_lb, bar_length_ft, sling_wll_lb, min_top_height_ft, sling_angle_deg
- Load split load split equally to two end pick points (W/2 each)first-principles
- WLL floor the sling WLL must exceed half the load; each top sling carries at least W/2 even verticalstatics