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RE: MASN - CUTTING OPENING IN EXISTING CMU WALL

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Richard,

This is a fairly common occurrence in the land of ungrouted and
partially grouted CMU.

Alt. #1 (No needles required)
Consider using the existing CMU as a lintel.  Design a normal reinforced
CMU bond beam and CMU jambs.

1.  Reinforce the jambs.
Cut vertical grooves in the CMU at the lintel bearing points.  Clean out
the void space, insert vertical rebar as required, place wood forms over
the grooves, and grout to the jambs to the lintel bearing elevation.

2.  Notch the existing CMU that will serve as the lintel.
Remove one face shell and the web of the existing CMU.  From the center
of the future opening, remove the outside face shell and web of half of
the opening and the inside face shell and web on the other half.  This
will allow placement of the rebar.  You will have to leave a sufficient
number of face shells in place to keep the wall stable.  If the load is
not too great, you might only have to leave only the center CMU face
shells in place.  Cut a hole in the webs that remain to allow rebar to
pass through.

3.  Cut openings in the CMU immediately above the lintel to allow the
placement of grout.

4.  Insert the required rebar. Clean out the CMU.  Place plugs in the
CMU cells immediately below the lintel.  Place new solid CMU soaps in
the lintel beam to replace the CMU face shells.

5.  Place the grout into the lintel beam through the openings
immediately above the lintel.

6.  Patch the grout openings as required with a stiff grout or mortar.

7.  After the grout has cured, you may then remove the masonry below the
lintel.  Trim the masonry, and patch as required with mortar.

Alt. #2 (Needles required)
Design a normal reinforced CMU lintel bond beam and CMU bullnose jambs.

1.  Install needles.
Provide openings above the bond beam and insert steel or wood needles
through the wall.  Shore and brace the ends of the needles.

2.  Remove the CMU as required for the jambs and lintel bond beam.

3.  Install a conventional reinforced masonry CMU bull nose jamb and CMU
lintel bond beam.  Grout can be placed into the cells through the same
openings used for the needles.

4.  After the masonry has cured, you may then remove the needles.  Trim
the masonry, and patch as required.

I hope this helps.

Regards,
Harold Sprague
Black & Veatch

 ----------
From: rlewis(--nospam--at)techteam.org
To: seaoc(--nospam--at)seaoc.org
Subject: MASN - CUTTING OPENING IN EXISTING CMU WALL
Date: Thursday, August 28, 1997 4:50PM

I have an existing 10" CMU wall I would like to cut an opening in.  The
wall
is not grouted.  It supports floor framing about 2'-8" above the
opening,
plus additional wall height.  I would like to cut a double door into the
wall.  Since the opening is so large relative to the distance of the
floor
load above, the floor load  must be support on the lintel (within the 45
degree triangle).  I would like to cut the opening into the wall on one
face
at a time.  I have checked precast concrete lintels but the shear is
just too
much.

Does anybody have a good procedure for cutting openings into existing
walls
supporting loads greater than the triangle arch above?  Any 2 piece
steel
detail that would not leave exposed steel?

Thanks for your help and input.
__________________________________________________

Richard Lewis, P.E.
Missionary TECH Team
rlewis(--nospam--at)techteam.org

The service mission like-minded Christian organizations
may turn to for technical assistance and know-how.