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# Ratchet strap coefficient of friction for Capstan calculation

## Ratchet strap coefficient of friction for Capstan calculation

(OP)
Hi All,

Apologies if this is posted in the wrong category... wasn't quite sure where to place it.

I'm trying to calculate the holding capacity of a heavy duty ratchet strap and the effect it would have being wrapped around a cylindrical object (steel bollard or scaffold tube), using the Euler-Eytelwein Capstan equation. To do so, i need to find a suitable friction coefficient for flat, 50mm wide polyester ratchet strap/webbing sling on steel.

There appears to be quite a bit of literature out there for ropes around bollards, obviously due to Maritime interest, but i suppose what i'm after is quite 'niche'. There are lots of strapping articles which point towards BS EN 12195, but i'm afraid i don't have access to it.

Possibly a long-shot, but if anyone could offer any suggestion at all, it would be greatly appreciated.

Cheers

Wise

### RE: Ratchet strap coefficient of friction for Capstan calculation

The friction coefficient should be similar to that of a rope of the same material and construction (woven or braided polyester). If the friction coefficient for the rope is adjusted for local crushing of the fibers, the webbing might have a slightly higher coefficient, since the contact pressure would less, so there would be less flattening of the fibers.

Rod Smith, P.E., The artist formerly known as HotRod10

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