Wire-Rope Breaking-Strength Estimate and WLL
Field estimate of wire-rope breaking strength and its working load limit.
Example
You enter
- Rope nominal diameter (in) 0.5
- Construction factor (tons/in²) 46
- Design factor (safety factor) 5
You get
- Estimated breaking strength 11.5 tons
- Working load limit 2.3 tons
Checked against published worked examples from: Anchor Marine & Industrial Supply (Houston).
Details, formula, and sources
ScopeA field estimate of wire-rope minimum breaking strength (construction factor x diameter^2, default 46 tons/in^2 for IPS 6x19 steel core, editable; fiber core and large diameters read high) and the working load limit at a design factor (default 5:1). An ESTIMATE only - the manufacturer's certified breaking strength governs, and unmarked or uncertified rope must not be placed in service.
Formula or tablembs_tons = construction_factor x diameter_in^2 (default 46 tons/in^2 for IPS 6x19); wll_tons = mbs_tons / design_factor (default 5).
Source and editionWire Rope Users Manual rule-of-thumb (by name); MBS = factor x d^2, no edition cycle.
Free accessAn ESTIMATE only; the manufacturer's certified breaking strength governs. Do not place unmarked or uncertified rope in service.
What governsEstimate. Head rigger and manufacturer working-load-limit charts govern. Inspect every piece of hardware before the show.
API field namesdiameter_in, construction_factor, design_factor, mbs_tons, wll_tons
- Construction factor the default 46 is the rule-of-thumb tons/in^2 for IPS 6x19 IWRC (steel core) near 1/2 in -- fiber-core rope runs about 7% lower (1/2 in: 10.7 tons, not 11.5) and the d^2 rule reads up to ~10% high at large diameters, both on the unsafe side; bright IPS, EIPS, and other constructions/grades differ - edit itWire Rope Users Manual
- Design factor 5:1 is typical for general rigging; the application and the AHJ set the required factorASME B30.9
- Estimate only use the certified breaking strength for any real lift; never use unmarked or uncertified ropemanufacturer certification