Could it be simply that these are the standard structural bolts?

Jeff
 

Take a look at some of these publications for more background:

http://www.boltcouncil.org/Publications.html

A325 and A490 are accepted specifications for high strength bolting applications.  That includes shear, tension, and combinations of shear and tension.  When bolts are subjected to shear, the faying surfaces of the two materials in contact are subjected to shear-friction.  The shear-friction resistance is increased by the clamping force of the bolts. The higher the strength of the bolts, the greater the friction interface.

Further, the higher strength of the bolt, the higher shear resistance of the bolt itself.

Using the two considerations, the high strength bolts under A325 and A490 are the better options compared to normal bolt strengths.

ummmmmm...

Would't this relate more to the undesirability of A307 than anything else..?


-MJC

   

See section 4.15 of this document...

http://books.google.com/books?id=Jnhsmzm_EJoC&pg=PA148&lpg=PA148&dq=A307+bolts+shear&source=bl&ots=KGAVL_BNN_&sig=JU8HC11rP-43tGxRCgDoXvudHRo&hl=en&ei=LhF3SrfiJY7kNZL0mLEM&;sa=X&oi=book_result&ct=result&resnum=6#v=onepage&q=A307%20bolts%20shear&f=false

Star please....

-MJC

   

Thanks for all the replies, I think I got it now.

Actually, a quick question based off my reading of section 4.15 in the link MJCronin posted.

Why is it claimed in the opening paragraph that in A307 bolts the amount of initial tension is small, yet in high strength bolts it is enough to be recognized. Isn't the tension ultimately up to the assembler? Or are they saying that snugging the nuts in high strength bolts produces an appreciable tension?

Bolts are preloaded to some fraction of their yield stress (usually between 50 % and 100 %).  Since the strength levels of A 325 and A 490 fasteners are much higher than A 307 fasteners, you get judgement words like "small" and "appreciable".

MJC,

Ur funnee.