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RE: Reinforced Concrete Blockwork Construction

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In many areas of the country horizontal reinforcement is installed in
U-shaped bond beam blocks as opposed to concrete tie beams.  On several
projects I have had 30'-40' high CMU walls that required the steel
reinforcement to be installed horizontally to span between to concrete
columns which supported the main roof girder truss.  The design is
almost exactly like designing vertical reinforcement.  In cases like
this, I usually installed vertical reinforcement at 48"-72" on center to
help distribute the loads evenly to the bond beams.  

When designing the wall to span vertically, the reinforcement is run
down through the CMU cells.  In addition, I will require horizontal
truss type joint reinforcement to be installed at 16" on center.  Many
jurisdictions and codes will require this horizontal reinforcement
regardless (although I feel If I have a bond beam every 24" on center
there is no need for it).  You also should avoid specifying ladder type
reinforcement as the truss type offers more of a resistance to
deflection than the ladder type.  Most of the codes that require
horizontal reinforcement are also requiring it to be truss type.  From
the way that I understand your design, you are requiring deformed bar
reinforcement in both directions.  If this is true, you are looking at
more of a two-way flat plate design.  I have not seen any design
requirements for this type of analysis based on CMU (only concrete).  It
may be possible to substitute properties in some of the plate analysis
software out there.  If you can analyze this, I'm sure the reinforcement
requirements would be less than a conventionally reinforced wall
(assuming there is a structural member on the sides that can
sufficiently resist the loads from the horizontal reinforcement
(especially the roof attachment).

As for ease of construction,  it does tend to be more difficult as you
have to plug all of the cells in each bond beam that does not contain
vertical reinforcement.  If the vertical cells are a maximum of 16" on
center, then you can grout both the horizontal and vertical
reinforcement cells in standard lifts (the bars are held in place with
hangers specifically designed for bond beams) without fear of voids.
Otherwise, you will have to grout each bond beam separately and the
vertical cells up to that point.  

-----Original Message-----
From: Harold Sprague [mailto:harold.sprague(--nospam--at)neenan.com]
Sent: Monday, July 26, 1999 2:16 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Reinforced Concrete Blockwork Construction


Frederick,

This type of construction is quite common in the US, but you can run
into
problems in the international community.  I had a similar problem on a
project several years ago in the UK.  

I don't know where you are building this, but you may have to cut your
own
bond beams.  I would suggest that you review the US Army Corps of
Engineers
details at
http://cadlib.wes.army.mil/cgi-shl/dbml.exe?action=Query&template=secure
.dbm

They have details and perspective drawings that explain the process.
The
Corps has the same problem of constructing reinforced CMU in areas that
do
not have the general practice.

Regards,
Harold Sprague


-----Original Message-----
From: Frederick Ellul [mailto:f_ellul(--nospam--at)hotmail.com]
Sent: Monday, July 26, 1999 2:00 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Reinforced Concrete Blockwork Construction



On a project I am currently working on I have specified reinforced
concrete 
blockwork walls reinforced with both the main vertical reinforcement and
also horizontal secondary distribution steel.

However the contractor has never used any horizontal steel in such
walls, 
and he is claiming that it is a very time consuming process.

Does anyone have any suggestions etc from past experience of how the 
construction sequence could be carried out...i.e. number of courses
infilled

at one time etc without the builder's breaking their backs etc ? Maybe
also 
a few things to look out for etc technically ?

I believe this type of construction is quiet common in the US.

Any help will be appreciated.


Thanks,

Frederick


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