Wire-Rope Sling D/d Bend Efficiency
Bend efficiency factor and reduced working load limit of a wire-rope sling from the D/d ratio, per the WRTB curve.
Example
You enter
- Catalog WLL, straight pull (lb) 10000
- Bend diameter D (in) - pin / load 3
- Sling diameter d (in) 1
You get
- D/d ratio 3
- Bend efficiency 70%
- Reduced WLL 7000 lb
Details, formula, and sources
Inspect every sling before the lift.
ratio = bend_dia / sling_dia; efficiency interpolated from the WRTB 6x19 / 6x37 D/d curve (1->0.50 ... 25+ ->0.95, plateauing below full strength); reduced_wll = rated_wll x efficiency.
Wire Rope Technical Board Wire Rope Users Manual (D/d bend efficiency) and ASME B30.9 by name; the curve ships as editable breakpoints.
The WRTB D/d efficiency curve is published guidance; ASME B30.9 is a consensus standard.
Estimate. Head rigger and manufacturer working-load-limit charts govern. Inspect every piece of hardware before the show.
Field names used by the API: rated_wll_lb, bend_dia_in, sling_dia_in, ratio, efficiency, reduced_wll_lb
- D/d curve editable [ratio, efficiency] breakpoints for 6x19 / 6x37 wire ropeWRTB Wire Rope Users Manual