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Post-Installed Anchors in "Cracked Concrete"

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Currently there are code changes in development that will dramatically
effect the future analysis, design, and use of post-installed mechanical
(expansion) anchors in "Cracked Concrete".  Some of the anchor types
effected by these changes are known by the generic names wedge, sleeve,
and drop-in.

Initially, these new standards are to be introduced as provisional
standards of ACI 318.XX.  Eventually, they will be incorporated into the
IBC XXXX.

The code changes were developed with the basic assumption that after
expansion anchors are installed (within a tension zone), cracks that
develop tend to pass through the anchor locations.   It is assumed that
anchor installation stresses also contribute to tension zone cracking
and that as much as 90% of all installed anchors will "attract" a crack.

It is anticipated, these code changes will require substantial
reductions in the tension and shear capacities of the most commonly
specified post-installed anchor types.  As a result, current anchor
systems will have inadequate capacities to meet designers/specifiers
needs.  New anchor systems will need to be designed to meet these new
requirements.

I have not seen any of these conditions myself, nor have I heard of this
ever happening in practice.  I would like to know if the potential
results assumed by these standards are supported by real-life anchor
performance.

Please, would all interested parties respond to the questions listed
below.  If you have any additional comments, questions, or opinions that
would promote further discussion on this subject it would be greatly
appreciated.

1.  Are you aware of a situation/installation where a tension zone
crack, through a post-installed anchor location, has contributed to, or
resulted in an anchor failure?

2.  Are you aware of a situation/installation where a tension zone
crack, through a post-installed anchor location, has reduced an anchor's
capacity (tension or shear)?

3.  Do you have any historical, real world data that would indicate
post-installed fastenings contribute to, or are effected by tension zone
cracking?

Thank you,

Kent Carlson, P.E.
STI Consultants


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