Need a book? Engineering books recommendations...

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

RE: Anchor bolt confinement in pedestals

[Subject Prev][Subject Next][Thread Prev][Thread Next]
	David Dickey,

		You wrote, "The original question concerns ties around
anchor bolts at the top of a
pedestal.  The title of section 1910.4.3 in IBC 2000 is "Anchor bolts in the
top of *columns*."  Since a column is defined as "a member with a ratio of
height-to-least-lateral dimension exceeding three", this provision won't
apply to most pedestals.

David Dickey
Lexington, KY"

		It has been about twelve years ago, so I do not remember
everything perfectly, but...
		We set less than two levels of a precast concrete parking
deck on a pedestal that was 28" x 28" and our column was 24' x 24" (of that
I'm pretty sure) when the ironworkers heard a loud crack. I think the
pedestal was about 3' tall; I pretty sure it was not nearly as tall as 3
times 28". The Code was BOCA, probably 1990.
		The contract drawings showed a group of ties near the top of
the pedestal, but they were not placed as detailed. The anchor rods ("anchor
bolts" back then ;-)) buckled and the steel shims crushed the pedestal
concrete, driving straight down into it. They ironworkers had done well,
with enough connections completed that the settlement did not induce the
column to fall or even lean, and the owner ultimately left the column and
deck around it 2" lower than the design elevation.
		We have had other pedestal failures. One column more
recently was being set on a wall pilaster and spalled the face, revealing no
ties near the top. We have been lucky that there have been no injuries as a
result of these or other pedestal failures under our buildings.
		At the bottom of all of our columns, there is a base plate
with deformed anchor studs and three ties grouped, and our concrete strength
is usually at least 1,000 psi greater (5,000 vs. 4,000) than the pedestals.
It has always struck us that there is no mirrored strength nor ductility
required in the foundation, so even though top pedestal ties are usually
called out, we were pleased to see the tie provision added to ACI.
	James L. Getaz, III, P.E.
	Shockey Precast Engineer
	V: 540-665-3204
	F: 540-665-3250

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at:
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*   Questions to seaint-ad(--nospam--at) Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: 
******* ****** ****** ****** ******* ****** ****** ********