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RE: Flat Slab Punching Shear Reinf.

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Are they specifically called out as "shear bars"?  How long are they...the
middle section as well as the end sections?  That shape looks like standard
shapes used for flexural bars (i.e. at the top for negative moments at the
supports and at the bottom for positive moments in midspan).  Your
implication is that they are relatively short bars JUST at the column, but
it is not 100% clear if that is really the case.

In response to your question...I honestly don't know if they are
"acceptable".  It could somewhat depend on the shape/length of the bar.  In
theory, if the 45 deg slope portion feel at the right place, it could resist
shear at a shear crack.

If you clarify, I might be able to see what I can find out from my sources.

Regards,

Scott
Adrian, MI

-----Original Message-----
From: William Haynes [mailto:gtg740p(--nospam--at)gmail.com] 
Sent: Friday, June 20, 2008 4:13 PM
To: seaint(--nospam--at)seaint.org
Subject: Flat Slab Punching Shear Reinf.


I am analyzing an existing slab for a change in occupancy load. The drawings
are about 40 years old and have a 9" thick flat slab with 15" square
columns. Over the columns they call for shear bars that are bent
longitudinal bars but there are not any stirrups. The "shear
bars" called for look something like this   ______/========\______.


I think I have seen bent bars like these in concrete joists to resist shear
in older drawings before. In my case, they are straight at the bottom, then
bend upwards at 45 degrees, are flat along the top over the column, then
bend down at 45 degrees and are straight again along the bottom of the slab.

Can you use bars like this under ACI today to resist punching shear in a
flat slab? ACI talks about longitudinal bars AND stirrups but the shear bars
they call for on these drawings are just several bent bars like I described
over the columns.


WH

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