"Machine Bolts" ASME structural engineering capacity in shear or tension

[adamewood]

I put quotations around the key phrase to hopefully help future structural engineers out (assuming this thread can generate some answers!) - as a google search of the thread's title + site:eng-tips.com generated 0 hits.

My specific question relates to the common structural engineering practice of taking the ultimate tensile capacity of machine bolts and dividing by 4 to get a "yield strength" … the particulars of the limit state seem to rarely matter according to the stamped calculations I have reviewed. I assume this is a provision of ASME or RCSC?

The bolts referenced here are ones specifically not covered under AISC or AISI provisions (think something along the lines of ASME B16.6.3 or similar). Considering how often I have to approve the use of such bolts, I am hoping to find a more thorough capacity calc other than "working load = 0.25 x ultimate", unless that really is how things work over in the ME world.

 

[desertfox]

Hi adamewood

Do you mean a working stress as opposed to a yield stress? The yield stress is a material property and nothing to do with dividing the ultimate tensile strength by 4.
In the mechanical world we often use a safety factor of 4 or 5 and it depends on the application and also what method is used for the tightening the bolts. If you were using a torque wrench then I would use say 4 because of the error in using torque to tighten the joint. If I was tensioning the bolts with a puller I might use a safety factor of 2 because tightening with a puller or tensioner is much more accurate. Go to this site it’s got a lot of useful information about bolts etc.

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

 

[JStephen]

I am not aware of any "common structural engineering practice of taking the ultimate tensile capacity of machine bolts and dividing by 4 to get a 'yield strength'".
In structural engineering, the bolts used are those specified in the structural codes, and ultimate strength, yield strength, and design strength provisions will be as specified by the codes used. And they are generally not just "machine bolts".
In pipe or vessel work, the bolts used will be those specified in the pipe or vessel codes, with properties varying accordingly.
In addition to ultimate strength specified, there may be differences in inspection, testing, traceability, dimensions, etc., so machine bolts shouldn't be substituted willy-nilly for structural bolts, flange bolts, etc.
If you can let us know more specifically what application you're dealing with, you may get better answers.

 

[adamewood]

I'd say the most common situation I've seen is with railings or infill - especially proprietary systems where the hole size and spacing is already set. In general these types of bolts tend to be called for wherever bolts 1/4" diameter or less are required, usually in situations where the backing is light gauge metal or wood blocking that is too thin for screws and applied loads are only a few hundred pounds. If you have ever hung a TV with backing plate from a wall bracket, that is the type of bolt I'm talking about (or maybe I have a small tv by 2021 standards).

This particular application is for hanging a glass partition. The holes are 12" oc, the fastener heads must be countersunk and 1/4" or 5/16" max diameter, must be attached to 2x blocking laid flat, and withstand 1.4 kips of pullout due to a 1" force couple which is thankfully resolved within the blocking itself...

Desertfox yes you are correct, I meant working stress (not yield). Tightening would be with a torque wrench. Also did you mean to paste a link (or perhaps my computer is acting up).

Thanks for the replies.

 

[desertfox]

Hi
Yes my mistake here is the link:-

https://roymech.org/Useful_Tables/Screws.html

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