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Concrete Anchors

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Mike,

We have used around 2-3 million of these every year for the past 35+ years,
some big earthquakes, and a lot of other abuse without reported incident.

ICBO (in their infinite wisdom) withdrew their "approval" of these for wind
and seismic loads in 1997, and it took several years and a lot of
laboratory money to test them again to seismic and cyclic loading. The
result? These same anchors are now good for 33% more than before 1997.

As for being in crack free zones: Concrete cracks. The tests were performed
in plain concrete samples with corrections for spacing and edge distance.
There are very few (and none in my experience) reported problems with being
near contraction or construction joints. The shear cone does not seem to be
sentitive to a vertical crack. Exactly why escapes me, but that's what
Mother Nature tells us in the lab, and in the field (where we often test
these anchors for higher tensions than allowed by ICBO). For example, I
have yet to fail a 3/8" diameter expansion anchor in tension if it is more
than 2" deep in the slab, regardless of proximity to any joints (the bolt
yields first), and routinely pull 10,000 pounds on anchors (with strong
enough studs) when 3+ inches in a slab.

On paper, cracking looks like a problem, but in reality, it isn't. Why, I
don't know, but that's the way it is.

Peter Higgins, SE

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