fatigue design of A307 bolts
fatigue design of A307 bolts
(OP)
I'm in search for design guidelines (i.e. allowable stresses) for A307 bolts subjected to cyclic loading (on the order of millions of cycles).
We are designing a retrofit of a large base plate anchored to a slab, with pretenstioned bolts. The drawings spec'd A325, but the fabricator supplied A307 and they were installed. Now, 25 years later, we discoved this snafu and have discovered that the bolts have yielded some and are causing problems. The bolts cannot be removed and we have been asked to design a retrofit to reduce the stresses in the bolts. Unfortutely, we cannot replace the bolts. We have inspected the bolts using ultrasound and have determined that they are uncracked and are usable, so long as we limit the stresses. Unfortunately, almost all bolt fatigue research has focused on A325 and A490 bolts.
So my question is, what should I limit my max bolt stress and stress range to avoid fatigue problems (on nominal or root thread area).
Thanks
Brian Rose
Structural Engineer
Simpson, Gumpertz and Heger
We are designing a retrofit of a large base plate anchored to a slab, with pretenstioned bolts. The drawings spec'd A325, but the fabricator supplied A307 and they were installed. Now, 25 years later, we discoved this snafu and have discovered that the bolts have yielded some and are causing problems. The bolts cannot be removed and we have been asked to design a retrofit to reduce the stresses in the bolts. Unfortutely, we cannot replace the bolts. We have inspected the bolts using ultrasound and have determined that they are uncracked and are usable, so long as we limit the stresses. Unfortunately, almost all bolt fatigue research has focused on A325 and A490 bolts.
So my question is, what should I limit my max bolt stress and stress range to avoid fatigue problems (on nominal or root thread area).
Thanks
Brian Rose
Structural Engineer
Simpson, Gumpertz and Heger





RE: fatigue design of A307 bolts
Af = pi / 4 x (db - 0.9743/n)^2
db - nominal diameter of bolt, inches
n - threads per inch
RE: fatigue design of A307 bolts
RE: fatigue design of A307 bolts
Regardless, the owner is stuck with mild steel instead of high strength steel, and we need a remedy. So back to my original question - any specs on max stress & stress range for A307 bolts or threaded rods made of similiar material?
RE: fatigue design of A307 bolts
I am unaware of any codes or standards dealing specifically with your problem. And I can't point you to any research papers.
If it was my problem, I'd use .4Fy maximum allowable stress on the unthreaded body and a maximum allowable stress range of not more than 10ksi.
But I think you need better advice than what I can give.
RE: fatigue design of A307 bolts
Basically, mild steel, ungraded threaded rod stock.
The key word is 'ungraded' and difficult to estimate allowable stress. I concur with watermelon, you need better advice than I can give.
Rod
RE: fatigue design of A307 bolts