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RE: CMU Wall Strengthening

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Rich,

The way we normally design steel strongbacks is to let them take all of the
tributary lateral load that would normally be resisted by the jamb steel.
If the steel member is not stiff enough maybe you could increase the size of
the member so that it is stiffer than the wall or determine that the extra
deflection is not detrimental to the CMU.

Jim Persing, PE

> -----Original Message-----
> From: richard lewis [mailto:rlewistx(--nospam--at)juno.com]
> Sent: Tuesday, September 09, 2003 1:28 PM
> To: seaint(--nospam--at)seaint.org
> Subject: CMU Wall Strengthening
>
>
> I have a shipping warehouse that has some problems with its masonry
> bearing wall.  The front of the building has 3 overhead door
> openings.
> The wall is 12 inches thick, 8" CMU and 4" brick.  The doors
> are 12 feet
> wide.  Two doors have a loading dock bumper height of about 3
> feet high.
> A third door opens on grade and is 14 feet high.  All door
> heads are same
> height.  The masonry pier between doors is 5 feet wide.  The remaining
> front of the building is a full height masonry wall for about
> 100 feet in
> length.  The wall height above the doors is about 9'-8".
>
> It appears that a truck has caught the side of the tall opening.  The
> masonry piers are out of plumb.  I dropped a plumb bob from
> the roof to
> the door head and the top of door head is about 3/4" out of
> plumb to the
> exterior face.  I dropped the plumb bob from the door head down to the
> ground and the wall went back in about 3/4".  The adjacent door was
> similar, slightly less.  The pier between the last 2 doors
> was about 1/2"
> out of plumb, same curvature as the first one.  As I progress
> away from
> the 14' high opening the out of plumb decrease, so it appears
> to radiate
> from this one door.  That's why I think a truck must have
> pulled out one
> door jamb.  The top of this jamb has severely cracked brick.
>
> My fix first is to repair the cracked brick.  The steel
> lintel above the
> door bears 8" on the jamb, the first 4" being on the cracked
> brick.  Then
> I think I should stabilize the masonry piers.  My thought is to use a
> steel 'strongback' on the inside face.  I envision a steel wide flange
> column bolted to the CMU wall.  I expect the top course to be
> a bond beam
> since steel bar joist bear on it.  I can attach the bottom to the
> concrete floor or a concrete wall at the base.  I would guess I could
> connect to the masonry wall at about 2' o.c. vert. with
> adhesive anchors.
>
> I want to get some feedback on what to design this 'strongback' for.
> Perhaps some of you have done this before.  The strongback
> will not be as
> stiff as the CMU wall so I don't believe it will take the lateral
> loading.  I guess it would just be for buckling stabilization
> so the wall
> does not get worse.  What kind of forces would this be?  Would one
> strongback per 5' wide pier be enough?
>
> Thanks for your help.  I really appreciate all the wisdom from your
> input!
>
> Rich
>
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