rope wrap on object and friction 2

[agodave]

The concept that I'm looking at is very simple but I'm want to put the numbers to it. If you wrap a rope around a pipe to hold a weight is there a formula to calculate the number of wraps resulting in the required holding force. I know I've use this many times in life but now it's time to put some numbers to it.

 

[satchmo]

T_out/T_in = e^{[μ][θ]}

Relates the in and out tension where

[μ] is the coefficient of friction between the rope and pipe and [θ] is wrap angle in radians.

 

[Tmoose]

I do testing in my own garage since Any believable formula for rope friction would have been derived from empirical data anyhow. Wet nylon can be pretty slippery.

Note satchmo's formula requires T in. After a few wraps the load can be stopped pretty easy with slight drag on the free end of the rope. 5 wraps of a rope with
? = 0.1 solves to more than 20>1 retarding ratio

 

[pauljohn]

Interesting thread from a marine point of view as we deal with this problem all the time. I do not know any technical data but here are a few practical things that I thought might affect your answer.

Some ropes are manufactured to maximise friction others to minimise it. Also the weave of the rope would come into play (3-strand, 5-strand, platt, etc).

Another problem is the diameter of the pipe versus the diameter of the rope. Also are you assuming the rope is always perpindicular to the pipe axis

 

[agodave]

I'm assuming that the rope is always perpindicular to the pull. The problems is actually a bit more involved but this part of it is based on the rope concept. You input has been very helpful. Thank you all.

 

[arunmrao]

When this posting appeared I happened to read it and did not appreciate much. However on the same day or the next there was an accident and 5 lives were lost and many injured as the wrap around rope gave way and the scaffolding collapsed. This happened in infosys campus at Bangalore.

 

[pauljohn]

arunmrao

can you supply link to article?

 

[arunmrao]

http://news.sulekha.com/nlink.aspx?cid=288876

http://www.thehindu.com/2006/12/14/stories/2006121419020100.htm

You can read the details as a news item in these links.

 

[arto]

Tie a clove hitch & don't worry ;-)