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Metal building frames blown over (was Levelling plates or shims ?)

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> From: "Sprague, Harold O." <SpragueHO(--nospam--at)bv.com>

> Good point.  Four bolts is a must!!  The OSHA Subpart R is now the law, and
> a good idea.  It is so automatic with me, I did not even mention it.

> For narrow bolt configurations that are popular with the 3 hinge arch frames
> for pre-engineered metal buildings, it can be even more critical.  I have
> seen frames like these blown over, and iron workers killed (Denver 1998).
> Engineers who design these structures should run the numbers for wind on the
> projected area based on a 5 year wind.  There will be a paper published soon
> correlating construction wind velocities to a 5 year wind.

Whack! Pre-eng takes another one up-side the head. Why doesn't anybody
say, "Look! Another poorly designed/erected conventional steel structure
just fell down ...?" 8-)

It is unlikely that wider spacing on the anchor bolts would have done
much in such a case.

Additionally, OSHA's requirement for 4 bolts is simply an improvement
over some of the more gross site stupidity and ignores the
wind/stability/impact forces (now, that's poor engineering!). There will
be erectors who assume that they don't have to provide bracing to those
columns since OSHA has mandated a "fix".

The wind susceptibility of metal building rigid frames is well
understood by most metal building designers. Unfortunately, it is not
well understood by some contractors and/or they try to cut corners by
ignoring the construction bracing!!!!!

Due to the deep sections commonly used, it can be possible to exceed the
surface area of the endwall, and/or the equivalent wind force of a fully
clad building, with just a few frames erected. It is imperative that the
first frame erected is well stabilized and the first pair of frames
erected includes the engineered building bracing. I have not encountered
a manufacturer that does not include this in the erection instructions.

Metal building manufacturers do not put any effort into construction
phase analysis except in very rare circumstances. The contractors are
rarely sophisticated enough to have it done or prefer to pay the
insurance premium, instead.

There was a failure, near Niagara Falls, last year. If I recall
correctly:
1) about 10 frames fell
2) there was no apparent bracing of any type installed, including the
engineered bracing
3) it happened on a weekend when nobody was on site (fortunately), but
it means that they left it that way, expecting it to stand.

The problem is not the framing style or quantity of bolts or spacing.
It's the occasional void under the hard hat.

--
Paul Ransom, P. Eng.
Civil/Structural/Project/International
Burlington, Ontario, Canada
<mailto:ad026(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>

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