Return to index: [Subject] [Thread] [Date] [Author]

Re: Anchor Bolt Splice

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Mr. Randolph,

I hope this helps

> 1.  How much thread should be showing above the nut to achieve full design
> capacity?

A:  Full design capacity is attained only with full thread engagement.  This
will occur just as the first 'starter thread' protrudes beyond the nut.

> 2.  Is there a documented relationship between the number (or length) of
> threads actually engaged and the design strength of the bolt/nut
interface?
> (i.e. a reduction curve when the bolt is shorter than required)

A:  There is such a curve, but it is a steep and slippery one.  One loses
more than just static load capacity.  For example, the failure mode switches
to thread stripping rather than bolt breakage, torque-tensioning
relationships change, succeptibility to vibration loosening is much greater,
etc.


> 3.  I'm thinking I'll have to weld an extension to the existing bolt.  Is
> there a prequalified full pen weld for two equal diameter rods?
> 4.  Will I need to preheat the base material?
> 5.  Will I need to specify special electrodes for the operation?

A:  Welding a heat-treated fastener is witch's brew in the making.  These
fasteners are tempered at just over 800 deg. F.  Any temperature exceeded
that will weaken the fastener measurably.  Full-size tensile tests of full
pen welded anchor bolts does sound like an interesting avenue of research,
however.  If you know anyone who would submit specimens, I'd volunteer to do
the testing in our lab gratis, as this is a topic that comes up regularly on
the construction sites I visit.

Now, the unpopular answer:  Being that the anchor bolts are manufactured and
represented as meeting ASTM A449, they would be covered under the Fastener
Quality Act.  Therefore, any person who alters them (as welding would do)
would be considered a "Fastener Manafacturer".  You don't even want to know
what all that entails --- other than any violation of those regs carries a
$25,000 fine.  Frankly, many of us in fastener manafacturing welcome (in
private at least) the provisions of this law.  We hold out hope that such a
law will limit our liability exposure when something goes wrong with one of
our products that someone else later alters.  In practice, it doesn't help
much, as lawyers draw in everybody no matter how obvious things are --- so
fastener manufacturers live with the understanding that once we put our logo
or name on a product ---- we're on the hook no matter what someone further
down the line does to the fasteners

In short, some sort of fully engaged coupling with adequate capacity would
seem the way to go.

David Sharp
VP, Engineering
TurnaSure LLC
57 E. 11th St. 8th Fl.
New York, NY 10003


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
*   site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********