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RE: ASTM A307 Bolts

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>A supplier on one of our projects is
>claiming that when we specify an
>anchor bolt comply with A307 he can
>supply an anchor bolt with rolled
>threads.  The motivation is that
>these bolts are slightly cheaper.  His
>argument is based on the claim that
>ANSI B1.1 (which we do not have a copy
>of) which is referenced from A307,
>reportedly lists rolled threads as an
>option.

Threads can be produced by cutting or rolling. The threading profile is
identical for both -- it has to be, since the product has tomate up properly
with a standard nut. Strength values are based upon the root area so the
strength then also is identical for both. We only use the nominal area as a
convenience in the calculation process. The design values include a
reduction for threading to get from that nominal area down to the threaded
area. This is in the AISC web site FAQ here:

    http://www.aisc.org/faq_popup.asp?id=189

To cut threads, you have to start with the shank diameter equal to the
outside thread diameter. To roll threads, you have to start with a shank
diameter that is intermediate between the outside tread diameter and root
diameter so that the material pressed in properly deforms out to match the
threading requirements. This is also in the web site FAQ here:

    http://www.aisc.org/faq_popup.asp?id=198

If it is desired to have rod tension yielding (i.e., stretching of the
unthreaded length) control the strength, the only way to do it is upset the
ends. Otherwise, essentially all deformation occurs in the threaded portion.

>This causes problems since the bolt shank
>is slightly smaller which results
>in a weaker bolt and results in a larger
>space between bolt and the bolt
>hole.

The bolt is not weaker because the critical section is always through the
threads. Unless you have a shear load at the column base, the slight
increase in clearance between the rod and hole is not an issue. If you have
shear, I would not recommend using bearing on the anchor rods to transfer it
anyway. Shear lugs should be used for significant shear. Smaller values can
be handled in a shear-friction model without a shear lug, though.

>I believe that the supplier is wrong since
>A307 specifies a minimum area
>and a tensile capacity which trumps B1.1.
>I may be wrong if the Minimum
>area is measured at the threaded region.

Chris Wright already commented on this. I'll only add my suggestion that you
consider using ASTM F1554 grade 36 whenever you would have used A307 before.
F1554 is a single-source document for anchor rods that gets you everything
you need in one place for threading (and heading, threading/nutting, bending
-- and two other strength grades as well -- 55 and 105). In essence, ASTM
F1554 grade 36 was written to replace and simplify anchor rods where A307 (a
bolt specification, primarily) material was being used. Grade 105 similarly
improves the situation where we used to use A193 grade B7. It's a really,
really good specification. More on it (and a few other new ones) here:

    http://www.engr.psu.edu/ae/steelstuff/astmspcs.htm

>Is the supplier blowing smoke or do we
>need to modify our specifications to
>exclude rolled threads.

He's not blowing smoke. In fact, he's probably given you some pretty good
insight into how anchor rods are made. Sometimes, you'll find you can learn
a lot from these folks, just as they can learn a lot from you.

I would not recommend excluding rolled threads for your projects. If you
did, I think you'd be doing something that is unnecessary and costing your
owner money in doing so.

Hope this helps.

Charlie








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