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Re: masonry wall openings

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Andrew,
I am specifically looking at the case of small holes less than 48" (48" x
48" max.).  The large retail door openings are a separate issue, and we
typically provide a steel lintel with full height elements each side for out
of plane force distribution to the supporting diaphragms.  I am in
California, and 90% of my work is in high seismic regions.

Standard practice on the west coast is to design for fully grouted walls.
In an "after the fact" situation it is difficult to know how the opening
will layout relative to the existing reinforcement until the opening is cut.
If we look at what you describe as an ideal opening,  the question arises
regarding compliance with the code requirement for continuous steel each
side of the opening and top and bottom extending 24" minimum.

If you determine the reinforcement locations one can argue that the
effective opening is larger than the actual opening and the reinforcement
exists for smaller openings, but as the opening size increases and the steel
layout becomes more uneven, the question of reinforcing the opening becomes
more acute.  Say the nearest vertical reinforcement is 24" from the edge of
the opening, this may be difficult to view as code compliant.

For small openings where the existing reinforcement is appropriate, we have
provided simple channel or tube frames within the opening (no extension).
As the opening becomes more difficult as described above we have provided
angle frames with the top and bottom angles coped on one leg to extend
beyond the opening for effective extension.

I am curious how others view and approach these situations.  We are
reviewing our standard approach and solutions.

Paul Feather PE, SE
pfeather(--nospam--at)SE-Solutions.net
www.SE-Solutions.net
----- Original Message -----
From: "Andrew D. Kester" <andrew(--nospam--at)baeonline.com>
To: <pfeather(--nospam--at)SE-Solutions.net>
Sent: Tuesday, November 19, 2002 6:47 AM
Subject: masonry wall openings


> Dear Sir:
>
> I read your post on the SEA list. We do renovations constantly to CMU
walls,
> so we have tried and done about every option out there (almost)! The
> reinforcing depends on what the wall is doing, and how it was built. The
> things to consider:
>
> -existing reinforcing spacing
> -out of plane flexure
> -shear wall
> -bearing wall- lintel is always necessary to shore up the masonry, even if
> it is just dead load of the CMU
>
>
> The ideal opening would situation would be a hole in a long wall that does
> not have a high shear in it. The opening would be smaller then the
> reinforcing spacing and would fit in between filled cells. Then you can
use
> angles or channels as lintels to shore up the opening. As long as the
> reinforcement was adequate and the opening does not cut through it, then
> that is about it. You assume the masonry in between the filled cells spans
> horizontally and carried the loads to the jambs. I personally do not
assume
> that CMU can span horizontally any span greater then 48" or the distance
> between required filled cells. However, there are references with formulas
> and tables for determining the load path more precisely. I take the easy
> route and make conservative assumptions as it rarely changes construction
or
> costs. HOWEVER, if the opening does need to cut through reinforcement, it
> gets a little more complicated because you have to give the wind/seismic a
> load path from the wall and opening, to the lintel, to the jambs.
>
> Sometimes we have to cut holes in walls for garage doors for retail
loading
> docks, and we have to shore up the opening with channels which are
designed
> for gravity loads and lateral wind loads. The lateral loads are often
taken
> care of with diagonal tube steel braces that carry the lateral load from
the
> channels up to the roof joists.
>
> If you give me some specific details I would be glad to give you my
> thoughts!
>
> Sincerely,
>
> Andrew Kester, EI
> Longwood, FL
>
>


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