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engineering training materials with respect to concrete masonry Kevin Fishburne 03-30-2007
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Posted by Kevin Fishburne on March 30, 2007, 5:39 pm
I'm putting together a design draft of a home for later submission to
an architect, and I'd like it to be as spot-on as possible without
having to become an architect myself in the process. The home is
primarily concrete block and heavy timber frame and I'm having some
issues with laying the CMU courses such that they're structurally
sound. I'm using 3dsmax to model it. The CMU pictured are standard
8x8x16 split-face blocks using stretcher bond. Here's a link to the
latest draft:

http://home-and-garden.webshots.com/photo/2116492180100974754zTVbAZ

My problem is how to deal with T intersections and in general places
that will require a half block to be used repetitively through the
courses. I understand there are steel ties that can bind a wall butted
to another wall in a T intersection if the blocks between them can't
overlap. I don't know where the half blocks should be placed as to not
affect the structural integrity of the wall though. I've heard corners
are bad places.

Does anyone have any suggestions as to how I can better design the
courses, or know or any reference material (online or in print) that
has good information about the structural engineering principles of
concrete masonry? Thanks all.

Kevin


Posted by Bobk207 on March 30, 2007, 10:21 pm
wrote:
> I'm putting together a design draft of a home for later submission to
> an architect, and I'd like it to be as spot-on as possible without
> having to become an architect myself in the process. The home is
> primarily concrete block and heavy timber frame and I'm having some
> issues with laying the CMU courses such that they're structurally
> sound. I'm using 3dsmax to model it. The CMU pictured are standard
> 8x8x16 split-face blocks using stretcher bond. Here's a link to the
> latest draft:
>
> http://home-and-garden.webshots.com/photo/2116492180100974754zTVbAZ
>
> My problem is how to deal with T intersections and in general places
> that will require a half block to be used repetitively through the
> courses. I understand there are steel ties that can bind a wall butted
> to another wall in a T intersection if the blocks between them can't
> overlap. I don't know where the half blocks should be placed as to not
> affect the structural integrity of the wall though. I've heard corners
> are bad places.
>
> Does anyone have any suggestions as to how I can better design the
> courses, or know or any reference material (online or in print) that
> has good information about the structural engineering principles of
> concrete masonry? Thanks all.
>
> Kevin

http://www.masonryinstitute.org/
http://www.orco.com/tech.htm
http://www.orco.com/tech_connect.htm


However........as we used to say in aerospace...... I think you're
getting bogged down in the "omega double dots"

I'll venture a guess that the placement of the half blocks are at
least a second order effect if the walls don't interlock / overlap
you're gonna have a gap. You're gonna have to make a connection with
rebar & at least local grout.

I'll also show my bias......CMU's aren't all that strong, if you want
real structural integrity, lay in some decent vertical & horizontal
rebar. And grout that puppy soild! :)

Of course, living in earthquake country can warp one's perspective :)

But tornadoes & hurricanes can be pretty nasty as well

cheers
Bob


Posted by Bob Morrison on April 2, 2007, 10:49 am
In a previous post Bobk207 wrote...
> I'll also show my bias......CMU's aren't all that strong, if you want
> real structural integrity, lay in some decent vertical & horizontal
> rebar. And grout that puppy soild! :)
>

CMU walls when properly designed and constructed can be very strong.

I have worked on two buildings in the South Pacific that were designed to
resist 130 mph winds coming off an open ocean (Exposure D). Reinforcing
was fiberglass rebar (GFRP) to resist corrosion.

In some remote locations like this the only reasonable method of
construction is CMU since everything must be carried by hand across the
reef and the beach. All mortar and grout is site mixed, but it comes in 60
pound bags that must carried one at a time.

--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com

Posted by Peter on April 3, 2007, 11:02 pm
wrote:


>
>CMU walls when properly designed and constructed can be very strong.
>
>I have worked on two buildings in the South Pacific that were designed =
to=20
>resist 130 mph winds coming off an open ocean (Exposure D). Reinforcing=20
>was fiberglass rebar (GFRP) to resist corrosion.
>

Briefly, what were the particulars of these buildings- height, wall
CMU size, horizontal and vertical reinforcing pattern? I'm curious
about the size and spacing of GFRP vs. steel as well as the
reinforcing requirements to counter the high wind design loads.

Posted by Bob Morrison on April 4, 2007, 6:40 pm
In a previous post Peter wrote...
> Briefly, what were the particulars of these buildings- height, wall
> CMU size, horizontal and vertical reinforcing pattern? I'm curious
> about the size and spacing of GFRP vs. steel as well as the
> reinforcing requirements to counter the high wind design loads.
>

Two-stories with floor to floor height of 12 feet. CMU is standard 8"
normal weight. As I recall (the project file is in storage) the vertical
reinforcing was something like #5 GFRP @ 16" o/c. Only the cells with
reinforcing (GFRP) received grout.

The GFRP was equivalent in strength to a Grade 60 bar. However, the
Young's modulus value is only about 6.5 x 10E6 psi, which makes the "N"
ratio about 2 instead of more usual 9. Deflection checks at services
loads become more critical.

At the time the design was done using Working Stress Design methods (had
to pull out an old test book and quickly relearn) because ACI had not yet
published ACI 440.

One of the more interesting details was figuring out how to hold down the
4x T&G cedar roof onto the Alaska Yellow Cedar glu-lam beams and then how
to hold down the beams to the CMU.

--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com

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