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Re: A325 anchor bolts

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A properly installed nut (at least flush the point of the bolt) develops 
the strength of the rod. There is probably some forgiveness in the nut 
strength for a thread or two, but I don't know how much off the top of 
my head. The Industrial Fasteners Institute (216/241-1482) may have a 
procedure for calculating the stripping strength of the threads based 
upon the actual length of engagement. Seems to me that is the kind of 
limit state that might sneak in with less-than-full engagement. With 3/8 
of an inch un-engaged, it's likely that you'll not have adequate 
strength.

So if you need to modify it, try a higher-strength thin-walled coupler 
with a threaded extension and washers stacked to bear the nut. The "A325" 
material you indicate is not suitable for a welded extension because it 
is heat treated. This lack of weldability is usually only a problem when 
you run into the field issue you've hit. I would also recommend against 
plug welds to "fill" the end even if the assembly were of a weldable 
grade.

Mis-set anchor rods are not all that uncommon, so I'd consider specifying 
a weldable grade of rod whenever possible in the future, just in case.

Note: I put A325 in quotes above because there is really no such thing as 
an A325 anchor bolt. A325 (and A490 for that matter) are steel-to-steel 
structural bolting specifications and can generally be procured only in 
bolt lengths up to about 8 in. or so. Also, these specifications have a 
very specific head size and threaded length. The head size is set for 
distribution of clamping pressure in a pretensioned installation, which 
is appropriate in many cases for a steel-to-steel structural connection, 
but not an anchorage application. The thread length is limited so that 
threads can be excluded from the shear plane when desired. Again, this is 
usually not applicable for an anchorage application.

I suspect that the steel fabricator probably "helped" you out by ordering 
A449 rod (the strength equivalent of A325 without the heading and 
threading requirements). FYI, A354 is the corresponding strength 
equivalent of A490.

By the way, there is a good discussion of the above issues in AISC's A 
Guide to Engineering and Quality Criteria for Steel Structures: Common 
Questions Answered. This book is available through the AISC web site 
(www.aisc.org) or pubs department (800/644-2400).

Charlie

Chris Palmateer wrote:
> 
> I have a job in which the contractor installed the anchor bolts for moment
> frame to low.  The bolts are 1-1/4 in. A325 with heavy head nuts.  How many
> threads does it take to fully develop the bolt?  If the bolts lack 1/4 to
> 3/8 of an inch from extending through the nut completely, how does one
> calculate the reduction in the capacity of the bolt?
>