Threading a solid round bar

[SteelPE]

I have a project where the client needs to tap their own solid material to form a nut and then thread their own rods to go into these tapped nuts. The material we are using is A304 stainless steel. I am wondering how one would go about making sure these items are capable of resisting the design loads imposed by them? ie, if the thread on the rod will be long enough/strong enough/not eat into the rod to reduce the tensile capacity of the member with the same questions for the tapped material.

 

[desertfox]

Hi

I guess provided the rods are the correct size then 1D thread engagement should be sufficient if the materials are the same or similar strength.

On the sketch you uploaded it looks like the tension is provided by winding the nuts down on springs, is that correct?
My concern in the above case would be the nuts winding off over a period of time unless you pin them in place after tensioning.

Galling issue could be overcome by using a lubricant on the threads during assembly however relative movement of the nut at a later date might gall particularly as the lubricant will have disappeared.

To be fair I'm not familiar with the construction you've presented but I'm just looking from a mechanical point of view.
Could the rods and nuts be made from carbon steel and plated to protect them from corrosion?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[SlideRuleEra]

Here are additional tips from Fastenal about stainless steel galling and how to reduce it: Link

Perhaps you could use stainless steel cable assemblies instead of rods, with stainless turnbuckles used for tensioning. This would avoid or minimize several problems:

1. The cables would not have to be custom manufactured. Threaded rods probably would.

2. Turnbuckles could be sized for the load, without the a limitation of thread size matching the rods.

3. If galling of turnbuckle threads or similar problems arise, they are confined to the turnbuckles or other fasteners which can be easily replaced.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[SteelPE]

dessertfox

After reading this stuff, I'm just a little paranoid about it. When the owner asked to switch the project over from carbon steel to stainless steel I though two things:

1) I never thought it would be this deep into details (I though it would be a similar process to carbon steel)
2) I though the fabricator would be more helpful as they specialize in stainless steel. Instead, they are just dumping everything in my lap which is frustrating.

I am probably going to specify similar threading to what is shown in the AISC table 7-18 (according to literature, this should help with binding. I'm also going to specify a lubricant be used during erection. I don't think the system will unthread itself, but maybe a binding nut is warranted to prevent movement of the system once everything is ok.

 

[berkshire]

Whilst I am not a structural engineer ,
I do have a lot of experience with sailboat rigging , both rod and cable. The biggest killer of stainless steel rigging is crevice corrosion. mostly in swaged cable fittings and turnbuckles. Basically anywhere moisture can collect without the presence of oxygen. An arrangement such as you are working on would require inspection at least once per year to look for the telltale brown marks of crevice corrosion, where possible type 316L is preferred over type 304L.
B.E.

You are judged not by what you know, but by what you can do.

 

[desertfox]

Hi SteelPE

This site give some info on minimising crevice corrosion:-

http://www.bssa.org.uk/topics.php?article=116

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Gumpmaster]

To answer your original question, FED-STD-H28/2B has the required calculations. The procedure & equations are in Appendix B.

I also, as others do, caution against galling.

I've seen several presentations from Halfen on their rod bracing system. It's pretty elegant. Check it out. It's available in stainless. Halfen Bracing. They have listed capacities and everything you'd need. Plus they look very nice.