Need a book? Engineering books recommendations...

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

Re: Embedded Anchor Bolts In Compression

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Check out "Strength Design of Anchorage to Concrete" by Ronald Cook, published by PCA.  The concrete crushing limit state under a bolt head (considerably higher than the general ACI equation for bearing on concrete) is given in Equation A-11a as:

Np = Ab*8*f'c

While this is for the strength of a fastener in tension, the same limit state should apply for compressive loading.  I would guess that compression bearing would not govern the design because there is an increased bearing area compared to the tension loading case (bearing area is reduced due to the bolt shaft).

Jason Emoto

>>> Bill Polhemus <bpolhem(--nospam--at)> 10/23/00 03:26PM >>>
I know we talked a little about this a few months back, but now that I have a
little more knowledge (a "little knowledge" being, of course, a dangerous thing)
about the topic, I'd like to recast the question I asked before.

In some instances there are advantages to NOT grouting structural column base
plates. For example, our stated DOT does not allow grouting of column base
plates for overhead traffic sign structures, which are typically hollow sections
and have cables or conduit running up into them from the bottom (the base plates
have concentric openings to allow this). They are afraid that condensed moisture
will build up inside the columns and cause accelerated corrosion.

Thus, no grout under the base plates, and the compression AND tension forces are
carried by the anchor bolts, the plate resting on the levelling nuts.

An embedded anchor bolt in compression would tranfer the column forces into the
concrete pedestal by bearing on the nut at the bottom of the bolt. But these
forces are bound to be large, and using the ACI code-calculated bearing strength
of the concrete under the nut (ACI 318-10.17.1) is not going to be sufficient
for such a force.

Does anyone have any experience with this? What did you use to determine

I seem to recall that research into anchor bolt failure mechanism showed that,
because of localized confinement, the bearing at the nut allowed was typically
on the order of many times the ACI 318 code calculation, when the bolt is in
tension. Not sure if the same would apply here.

Look forward to your input.