Spreader Bar vs Lifting Beam Below the Hook
Top sling tension, spreader-bar axial compression, lifting-beam bending moment, and headroom for a wide load from one hook. ASME BTH-1 / B30.20 and the rating plate govern.
Formula and source
sling_angle = atan(top_height / (bar_length/2)); top_sling_tension = (load/2)/sin(angle); bar_compression = (load/2)/tan(angle); beam_moment = (load/2)(bar_length/2); headroom = top_height.
ASME BTH-1 (Design of Below-the-Hook Lifting Devices) and ASME B30.20 by name; first-principles statics.
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