Structural Bolts vs. Grade 5 Bolts 3

[cadman5150]

Can anyone tell me the difference between a Structural Bolt and a Grade 5 bolt of the same size?

I am a Mechanical Engineer working for a company that manufactures heavy duty, industrial shelving…all bolted together.

These shelving units are required to hold very large loads placed upon them (2-5 tons).

The bolts in question are used to fasten the base to an upright verticle column, creating esensially an inverted "T". The head and nut distance across the flats, for the Structural Bolt is 1.25", whereas the distance across the flats on a grade #5 bolt and nut is 1.125".
So...the question is:
Is there sufficient surface contact under the head of the nut and bolt (grade 5) to create the suffient "friction fitting", between the two members (base & verticle upright), so they can't "shift"?

Any idea how one would calculate the force (torque) needed to achieve this?
I could only imagine that it would have to do with the total surface area of the two plates (and surface condition/finish) vs. the surface area of the head of the nut/bolt and its compressional strength, and of course, how many were being used. In this case, the two plates are 8" x 16" (128 in/sq surface area). They are fastened together using (4) 3/4" dia. bolts. The material is just CRS, powder coated.

I’ve noticed recently that when these units were originally designed, they were designed using “Structural Bolts” and at some point over the years they were changed to Grade 5 Bolts.

I am concerned as to whether or not the structural integrity of the unit has been compromised.

Can you help?

 

[Mandrake22]

What you probably want to consider is the clamp load of the four bolts multiplied by the coefficient of friction of your clamped parts. If you are using coarse threaded bolts, the clamp load at 150 lb-ft torque is 14400 lb. each. For fine thread it is 16375 lb each at 180 lb-ft. If one assumes a .20 cf, then the total restraining force would be 11520 lb. for coarse and 13100 lb. for fine threads.

 

[cadman5150]

Thanks Mandrake22!
That is EXACTLY what I was looking for!
I have spent 10 years in Automation and know I can't remember how to work this stuff anymore...thanks for your help.
Is there a specific formula or table that you used to come to this?

 

[Mandrake22]

Glad to hear it helped.
I got this from my wrinkled, dog eared, yellowed, faded, coffee stained page that was Xeroxed from somewhere long since forgotten!
I just Googled this page which, oddly enough, has the same values I quoted!

http://www.team.net/sol/tech/torque.html

 

[cadman5150]

Very cool!
I'm new to this forum. I hope that I can be of assistance to someone in the future!
Thanks again!

 

[plasgears]

In automotive work grade 5 is chosen for important clamping requirements. Grade 8 is the ultimate bolt for critical assys like seat belt support. They have distinctive markings on the head to tell them apart.

 

[cadman5150]

Thanks "plasgears". I appreciate your response.
I have, however, been finding quite a bit off information over the last few days and , apparently, there's not a whole lot of difference between a Structural (A325) Bolt and a Grade 5 Bolt. Both, basically, have the same qualities, with exception to the head and nut size.
And, yes, you are correct...a Grade 8 blows them both away!
Thanks again,
cadman5150

 

[dmalicky]

Here's what I've learned...
A325 is different than grade 5 in these ways:
- Better quality control (since they hold buildings together).
- Heavy hex head instead of standard (as you found)
- Less thread length so you can use more of the shank for shear.

A few caveats on the above discussion...
Grade 8: the #s look good but if they are plated they can be prone to hydogen embrittlement. Also, the lower quality control (esp. in import fasteners) can mean lack of ductility, plated or not.

Torque: unfortunately not very reliable as a measure of actual bolt tension. If tension is critical you can use a load indicating washer, or appropriate Belleville.

A great summary of bolt info is at

http://www.fastenal.com/web/documents/FastenalTechnicalReferenceGuide.pdf

(esp. p. 16-24)

 

[cadman5150]

Thank you "dmalicky"!
An EXCELLENT source!

 

[evelrod]

cadman5150, the FAQ section of this forum has several good things to look over. As to A-325 and A-490 consturction grade fasteners, they can be had in a variety of shank and thread combinations as can automotive grade 5. A-325 and Grade 5 markings are the same as is their quality (depending more on the mfgr/country of origin). A-490 would be equivilent to grade 6/7 I suppose. Automotive Grade 5 can be had in a variety of head thickness (may require a bit of shopping around). Grade 8 bolts are the highest graded bolt that is not individually inspected (aside some branded fasteners, eg, "Supertanium" which, presumably, exceed Grade 8 specs). NAS graded bolts are next and they are individually inspected as is required in aerospace construction. Read that "expensive" unless you shop surplus stores as I do. Lots of gov't. waste shows up in these "surplus" shops.

Rod

 

[evelrod]

I am sorry. Try the FAQ section of the "Welding, Bonding and, Fastener engineering" forum.

Rod