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Re: CMU Wall Strengthening

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Rich,

I think Roger hits on an interesting point in his first paragraph.  Are
you really sure that your problem is due to a truck hitting the door?

I also want to make sure that I am understanding correctly...the wall bows
outward (i.e. away from the interior of the building).

Back to Roger's point...is the wall a composite wall system where the
brick and CMU are designed to act together (i.e. is there a collar joint)?
Or is it meant to be a multi-wythe wall with the CMU meant to be the
structural element with the brick just meant to be the facia?

If the latter, then your problem may be caused by differential movement
that then got "exacerbated" by the lintel bearing on both the brick and
CMU.  Keep in mind that brick will tend to swell due to moisture and heat
more than CMU.  As a result, the brick part of the wall will tend to
"grow" more than the CMU part of the wall.  If this movement is not
permitted to happen in the vertical plane, then a brick wall may try to
bow outward.  You know that you have at least one place where the brick
CANNOT move vertically relative to the CMU...at the lintel.  Are there
other places (i.e. at the top of the wall where the joists bear)?  If the
walls are then tied together with brick ties, it could also then "pull"
the CMU wall outward with it.  To some degree, this scenario could be
"reinforced" by the presence of the cracked brick.  The cracked brick
could be due to excessive compression stresses in the brick due to it
trying to move upward but being restrained by the lintel.

To me, if a truck had done it, there would likely be more local damage at
the location where the truck had "pulled" or hit the wall.  Additionally,
unless the truck "caught" at the top of the openning (which is definitely
likely), I would think that the "bow" of the wall would be more offset
such that the maximum lateral movement would be lower...closer to being
centered on the door opening rather than the full height of the wall.

Now, if it is the former, then this is still a possibility of the problem
being due to the same type issue depending on the strength of the collar
joint (assuming that there is one...maybe the intent was to have a
composite wall but the execution did not follow the intent).  But, if it
is the former, than brick swelling becomes a less likely culprit (again
assuming a "proper" composite wall exists).

If the problem is really due to brick swelling/movement, then the
strongback won't completely solve the problem.  It might help prevent a
catistrophic (sp?) failure, but likely there will be future cracks or even
bowing of the wall if there remains a "hard connect" between the brick and
CMU.  So, if brick swelling/movement is the issue, then you would also be
best served by finding a way to isolate the brick from the CMU for
vertical movement at the steel lintel (i.e. don't bear the lintel on the
brick).

I would suggest that you take a closer look and really make sure that you
have found the real problem.  Is there any other evidence that really
suggests that this was due to a truck hitting the openning or wall?  Do
you have a witness that is willing to admit it?  Have you checked other
areas of the building to see if there are signs of the brick bowing
outward (i.e. did you ONLY look at this door area or did you check the
other doors or even other parts of the building)?  Are there other signs
of brick distress at this location or others, such as cracks or spalling
brick?

HTH,

Scott
Ypsilanti, MI


On Tue, 9 Sep 2003, Roger Turk wrote:

> Rich,
>
> I have no suggestions on fixing the out-of-plumb wall, but I would be
> concerned with the lintel bearing partially on the 4" brick and partially on
> the 8" cmu.  With the wall being 12" total thickness, it seems that there
> isn't any room for a grouted collar joint.  Is the inside of the cmu also
> bowing or is it just the brick wythe?
>
> At this point you probably should also look into why a truck would hit/hook
> onto the wall.  If the doors with the loading dock have a depressed ramp, it
> doesn't take too much of a slope (2:12) for the top of a truck to project 2'
> beyond its bed.  If you don't provide for a dock extension and bumper system
> or large bollards, a truck is again going to hit the wall.
>
> HTH
>
> A. Roger Turk, P.E.(Structural)
> Tucson, Arizona
>
> Rich Lewis wrote:
>
> . > 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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