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RE: Min. masonry reinf

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Ted,

It is a good and valid point.  It is more of an issue with high lift as
opposed to low lift grouting.  With the fins, a vertical bar, and 2
horizontal bars, it does get congested.  

Assume a wall is 16 feet tall, with bond beams at 4' on center.  The grout
in high lift must travel around several bars in bond beams.  If the bars are
placed accurately with the fins all knocked down, you have less than 1 1/2"
between the wall and the face shell for the grout to flow and the vibrator
to pass.  Generally low lift would be done in 4' foot lifts making grout
consolidation much easier.

The point is that it can be done, but it does force a process.  In the land
of partially grouted walls, low lift is more common so the impact is less.
In the land of fully grouted walls where high lift grouting is more common,
the forced process of low lift grouting will probably cost more.  If you
don't need the two bars at a single elevation it is better to stack the 2
bars and eliminate the problem.

On the corollary issue of partial versus fully grouted walls, the only place
that I have used fully grouted walls solely because of local practices was
in California.  That said, another mitigating factor was the lack of seismic
testing on partially grouted walls.  That is not to say that partially
grouted walls will not perform properly, it only says that the seismic tests
have not been performed.  But theory says that partially grouted walls
should work fine.  By the way, another argument for partially grouted walls
aside from being cheaper to build is the insulation value.

One other point that should be made is that intermediate bond beams do not
use a U shaped bond beam regardless of what the vast majority of structural
drawings show.  They use a knock out bond beam unit that has the webs scored
to allow the mason to knock out the top half of the web. Normally the mason
places the horizontal Reba directly on the knocked down webs.

If U shaped bond beams were used, it would not allow the vertical flow of
grout, and it would require the mason to drill holes in the bottom to allow
the rebar to run through.  It just doesn't happen that way, but 95% of
structural and architectural drawings show the U shaped bond beam for
intermediate bond beams.  The U shaped bond beams are only used at masonry
openings.

There are a whole bunch of viewable good constructable structural masonry
details in Microstation or AutoCAD on the Corps site at
http://cadlib.wes.army.mil/cgi-shl/dbml.exe?action=Query&template=/detlib/cd
l_std.dbm that illustrate some of the points above.


Regards,
Harold Sprague, P.E.
The Neenan Company
harold.sprague(--nospam--at)neenan.com


-----Original Message-----
From: Partrick, Ted [mailto:ted.partrick(--nospam--at)ci.greensboro.nc.us]
Sent: Monday, December 07, 1998 9:04 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Min. masonry reinf


This is a little late to bring up in this thread, but here goes:

In a seminar put on by our local concrete association on concrete masonry,
an masonry consultant with the portland cement association recommended that
two re-bar never be used in horizontal applications in an 8" cmu wall unless
they are stacked vertically (one above the other in the block). His
explanation was that in many applications the bars create congestion and the
risk is high that the block will not be fully grouted. In the u-block used
for many lintels, there is not a lot of space in the bottom of the block. 

Do those of you with inspection experience in cmu construction find that
2-#6 bars placed horizontally can be reliably grouted?

Ted