Allowable external load for grade 5 bolts

[BillyNuclear]

My overall problem is that I'm using grade 5 bolts that will be subjected to tension and shear or in some cases just tension. I can't find any guidance on how much external load is allowed. AISC 9th edition lists formulas for allowable tension stress in table j3.3 and allowable stress in table j3.2, but they don't list grade 5.

1) Since Grade 5 bolts have the same mech properties as A325, can I use the equations listed for A325?

2) Do I compare my calculated stress from my EXTERNAL load and compare it directly to the value I get from these equations? In other words, what assumption is the equation making about how tight my bolt is? Turn of the nut method?

Thanks

 

[desertfox]

Hi BillyNuclear

The bolts you are using should be pre tensioned or torqued up to produce a preload greater than that of the external force that will be applied to the components in the assembly.
When the external load is applied it will be shared between the bolts and the joint materials in proportion to the stiffness of the bolts and jointed components.
Check out this site below:-

http://www.roymech.co.uk/Useful_Tables/Screws/Preloading.html

So the total load in the bolts will be the preload + a proportion of the external load.

If you can provide more information I might be able to help further but I don't have access to AISC codes.



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

 

[thaidavid40]

Are these Grade 5 bolts going to be used in a structural application? If so, then why not use an A325 bolt instead? If it is not a structural connection, then the AISC provisions wouldn't apply. Be careful, as A325 bolts are often tightened to a pretension load (beyond the yield). I'm not sure that Grade 5 bolts are approved for such purposes. Also, the heads on Grade 5 bolts and nuts are smaller than A325, so that might also play a role in their allowable pre-tensioning loads.
Dave

Thaidavid

 

[BillyNuclear]

My application is an above ground steel storm shelter. Only big enough for two people. Not sure if this is considered structural or not. It doesn't really seem to fit much of what's in the AISC manual. Also, the customer wants to use carriage bolts so the shelter can act as a safe room and not allow someone to remove bolts from the outside. Carriage bolts are not offered as A325, but are offered as grade 5.

Also trying to avoid requiring a torque value. Somehow the other manufactures of these shelters have figured out a way to do this without requiring a torque. They claim all you need is a regular wrench. Plus advertise grade 5 bolts. Not sure how they're doing this.

Thanks

 

[desertfox]

Hi BillyNuclear

If you don't know what the external load for the shelter is going to be then I cannot see the point in trying to obtain what the allowable external bolt load is and in addition if you don't tighten the bolt on assembly so that the bolt preload is higher than the external service load, then the joint is liable to separate and eventually fail.

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

 

[BillyNuclear]

I do know the external loads. I also understand the idea about pretension. But in structural applications a torque value is not specified. How do they get away with that? And why can't that same idea be applied to a grade 5 bolt? Trying to avoid specifying a torque. Not sure how accurate it would be anyway. Thanks.

 

[thaidavid40]

@BillyNuclear,
They "get away with it" through rigorous testing and research. The RCSC bolt specifications documents will tell you everything about fully-tensioned A325 bolts for structural connections. I am not aware of any similar testing for Grade 5 bolts for structural connections, though they may exist somewhere. In any event, A325 bolts can be reliably tensioned by the relative turn of the nut (within the guidelines of RCSC) to produce yield stresses guaranteeing a maximum clamping force.
Dave

Thaidavid

 

[desertfox]

Hi

In structural applications they do what's called "snug tight" the bolt is tightened down and then given a certain amount of turns of the nut and that's usually very consistent

https://www.aisc.org/DynamicTaxonomyFAQs.aspx?id=1762

https://books.google.co.uk/books?id...Ch0wxwl4#v=onepage&q=snug tight bolts&f=false

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

 

[BillyNuclear]

So in every application other than structural, a torque value should be specified?

 

[thaidavid40]

I don't know how to answer your question as asked, but I can say that you can use the A325 bolts per the structural connections guidelines in the RCSC and AISC documents. There are no other applicable bolting documents to apply directly to structural connections (from a code standpoint). You can use your engineering judgement, and any other test results you can find regarding the Grade 5 bolts, but this is not the same as using code approved procedures and requirements - unless you perform your own tests and submit those documents to the AHJ.
Dave

Thaidavid

 

[BillyNuclear]

Thanks for the input

 

[desertfox]

Hi

A torque figure is not always needed, it depends on the criticality of the joint, if the joints fails what damage will it do? will it kill someone or do a lot of damage to equipment? these are the things you need to consider.
Now if you want to use grade 5 bolts and you know the loading that the joint will see its reasonable to workout what the stresses might be using a lower grade bolt.

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

 

[desertfox]

hi

I find this site warning about using bolts with the same grade material

https://www.fastenal.com/en/79/structural-bolts

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