Spreader Beam Minimum Top-Point Height
The inverse of the spreader-beam tile: the minimum top-point height so the top-sling tension stays within the sling WLL, since 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 and source
angle_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.
ASME BTH-1 (Design of Below-the-Hook Lifting Devices) and ASME B30.20 by name, solved for the top-point height; first-principles statics.
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