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Re: half height steel nuts

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I love M.E.s :o) Very nicely done Chris.
Chuck Utzxman, P.E. (C.E. & M.E.)

Christopher Wright wrote:


On Nov 17, 2005, at 12:14 PM, Eli Grassley wrote:

I can’t find any equations on nut strength in the AISC code.

I hope you've stopped looking--there aren't any. ;->
Try the section on bolts and nuts in _Machinery's Handbook_. It shows detailed calculation procedures for tensile and stripping strength including the effects of thread allowances. These procedures are general and are used to provide the 'stress area' noted in the AISC Handbook.

Some things you might want to consider when you use half height nuts--
--You probably won't have the stripping strength to obtain a correct pre-load. If preload is important--if you have cyclic or intermittent loading--you stand a good chance of fatigue failures or having the connection unscrew itself, **especially** under tensile loading such as a suspended weight. I'd never use such a detail without a positive means to lock the nut in place such as safety wire or staking the threads. --The effects of the imperfect threads at the nut faces become increasingly more important as the number of engaged threads decreases. Don't assume that the half nut is completely threaded along its whole depth. --The working assumption is that the load is shared by all threads. This isn't true because of stiffness considerations; if the material is sufficiently ductile the load at failure is usually shared, but not the service loading where the behavior is elastic. With fewer threads the load transfer from thread to thread isn't gradual and failures tend to be sudden and consequently mor liable to be catastrophic. Be careful that your career isn't hanging by a single thread. (heh-heh. get it? single thread? That's bolting humor--the fun never stops.)

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/


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