Nuts Pulling Threads off of Threaded Rods
Nuts Pulling Threads off of Threaded Rods
(OP)
I have a detail on a project where I am hanging a wood beam from a steel bent. The hanging mechanism is a group of four, 5/8" diameter A307 Threaded rods with nuts on both ends.
The comment the framer made was "wow, that is not a lot of thread holding that whole roof up". As I looked at it, the nuts did look "normal", albeit narrow. For a 5/8" diameter bolt,
the nut has 9/16" of width (parallel to the threaded rod). We will add another set of nuts for safekeeping, but it occurred to me that the design values I was using was for the rod.
Is there another set of values I should be looking at for the thread/nut interface? Are nuts sized so that the rod fails before the threads strip out?
The comment the framer made was "wow, that is not a lot of thread holding that whole roof up". As I looked at it, the nuts did look "normal", albeit narrow. For a 5/8" diameter bolt,
the nut has 9/16" of width (parallel to the threaded rod). We will add another set of nuts for safekeeping, but it occurred to me that the design values I was using was for the rod.
Is there another set of values I should be looking at for the thread/nut interface? Are nuts sized so that the rod fails before the threads strip out?






RE: Nuts Pulling Threads off of Threaded Rods
What grade of material are the nuts made from?
Normally if the nut and threaded fastener are the same grade or very close then the threaded rod should fail first.
desertfox
RE: Nuts Pulling Threads off of Threaded Rods
I used threaded rod for temporary supports for bridge falsework for years. The manufacturer of the threaded rod and nut should be able to give you the safe working loads. For example, Dayton/Richmond (could be another name now as it has been 10 years since I have worked with it), specified its safe work loads for 1/2 rod at 9,000 lb tension and the standard nut at 6,000 lb for 1 nut or 9,000 lb for two nuts and for a heavy coil nut, 9,000 lb for one and 18,000 lb for two.
Also, I used 4"x5"x5/16" washers for all the connections to distribute the loads to the supporting members better than a standard washer, but the manufacturer should be able to guide you with that also.
RE: Nuts Pulling Threads off of Threaded Rods
RE: Nuts Pulling Threads off of Threaded Rods
RE: Nuts Pulling Threads off of Threaded Rods
for example, see this chart for both total strength ans pullout load from concrete:
http://www.strongtie.com/products/anchorsystems/ad...#
RE: Nuts Pulling Threads off of Threaded Rods
The Nut and washer are A307 and F844 washers. The properties can be found here:
http://www.portlandbolt.com/technicalinformation/a...
The loads given are allowable loads.
RE: Nuts Pulling Threads off of Threaded Rods
RE: Nuts Pulling Threads off of Threaded Rods
RE: Nuts Pulling Threads off of Threaded Rods
But, if you torque a double nut against each other, the load between the two double nuts is actually increased. yes, there are more threads to engage the threaded rod overall, but ONLY if both nuts have the same force (load) on the rods. Make sense? If one is tighter than the other, then it will carry the load, the second has none. If the lower is torqued up hard against the upper, then you are actually pulling the upper down and the lower up, and so the local stress on the rod between the two is greater than the original single-nut condition.
If I really, really had to do this, I'd get an extra long nut like a coupling nut.
RE: Nuts Pulling Threads off of Threaded Rods