double locking nuts

huangyhg

double locking nuts?
silly question.....say you have a threaded rod hanger connection in which a threaded rod is supported by a glulam beam.  the glulam beam would have a vertical hole drilled thru the cl of the beam width, the rod would be passed through and then hung with a nut and washer on top of the beam, (and probably a nut and washer below the beam to prevent upwards movement).
to prevent the rod from working itself loose, i was going to call up a double nut above and below the glulam.  this would "lock" the connection right?  i seem to recall that when you thread a single nut onto a threaded rod, tighten it to make the connection and then put a second nut and tighten it up snug to the first nut, the second nut would prevent the first nut from coming loose since they would tighten against each other????  i can't really visualize it in my head...maybe i should try it out for real!
check out our whitepaper library.
is this a structural application?
i would agree that the double nut will hold together and hold well, but i cannot quantify this holding force sufficiently to give an engineered value - off the top of my head.
will the rod be subject to cyclic loading? i think there is a world of parameters to be considered. that said, i have used similar details used to suspend conduit, duct work, and a thousand other things that would not be considered structural.
daniel
double nuts (also a product called jam nuts) are effective. here is a quote from kent's mechanical engineers' handbook, twelfth edition (wiley handbood series): "jam nuts used in pairs or in conjucnction with plain nuts develope internal 'locked-up' stesses when tightened against each other, furnishing the necessary pressure against the threads regardless of the bolt load. load is carried by the outer nut."
as an alternate, perhaps you could consider using a chemical locking compound, such as "loctite" on each (single) nut. it comes is various strengths, including one that is effectively permanent.
in some applications (where the nuts will be somewhat permanenet) we have requested that the contractor destroy the threads above the bolt.  they can do it in a lot of ways and it is pretty easy, but it is not for something someone is going to put up and take down every day.
akastud
i have used several techniques in the past. here are few:
1. i used jam nuts (mentioned by slideruleera
2. double nuts
3. upset the threads so that the nut would not back up
4. cotter pins
each method has its proper application. keep in mind maintenance and future re-work because some of these methods are permanent once installed.
good luck
if your loads are vibratory consider locking compound (locktite) and proper torque.  we have found that as the best connection.  there are several grades of thread locker compounds depending on the application.
actually i am not too worried about vibrations.  the hanger rods support a steel plate frame which acts as a sun shade, and the sun shade frame will be lag screwed into stud wall to keep it from moving laterally.
thanks for all the helpful posts....once again i am impressed by the depth of knowledge available out there!
karlit---i am somewhat curious about this connection.  why a "verticle" hole through the glulam?  having installed several "cat walks"  under the roof of several buildings at universal studios in years past---most were on "u" shaped hangers on thru-bolts "horizontally" in the glulams or with the hanger in single shear off one side of the thrubolt.
at any rate, all the threaded rods were either double nutted or had the threads compromised in some way to preclude loosening.  the only time i used a chemical locking agent was on the ss/glass canopy at the moca in downtown l.a. where the rods were double nutted and chem-locked.
rod
rod
the glulams are actually 5 inches wide by 6 inches deep, framing between glulam trusses, and for appearance reasons the architect doesn't want to see a steel bolted plate on the side of the glulams.  the rods are supporting lights for a gymnasium.
oops!  i am mixing up two projects....i am using the rods to support a sun shade in one project and the rods will also support gymnasium lights in a separate project.
how about a binks nut. that is a nut that is part squashed to an oval and after a couple of turns becomes very tight. or how about a nyloc nut which has a plastic insert to create a stiffness on the bolt.