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Re: Cracks in Concrete Column

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This post from Lloyd made me think of another possibility. Assuming the column base is configured similar to this, it is possible that the steel sleeve has begun to corrode. Corrosion is most severe at the ground level, where the column base joint occurs. The corrosion would cause a radial expansion, which would cause radial cracks in the concrete. These would appear primarily vertical on the face of the Colum, and would be most noticeable at the column base. If this is in fact the situation, it would seem to raise some serious concerns about the integrity of the columns. Significant cracking suggests a lack of confining reinforcing at the column base. So, if the concrete at the bearing point is cracked and unconfined, it could easily crush and drop the column. I agree with Rich about wishing I had a resource showing pictures of a variety of cracks in concrete, with an explanation and discussion of each. It seems that I am looking at some type of cracked concrete about once a month, and I'm supposed to come up with something intelligent about each one. I've learned a lot over the years, but I still feel as though I've only experienced the tip of the iceberg relative to the number of possible situations.

Dmitri Wright, PE
Cascade Engineering, Inc.
245 SE 4th Ave, Suite A
Hillsboro, OR  97123-4033
dmitri(--nospam--at)cascade-structural.com
503-846-1131





From: "Lloyd Pack" <packman90(--nospam--at)qwest.net>
To: <seaint(--nospam--at)seaint.org>
Subject: Re: Cracks in Concrete Column

Hello Rich,

As I read your post, I thought about how a precast column would
be attached to the foundation.  I thought that it might be connected
using a mortise and tenon joint.  If the tenon was protruding from the bot=
tom
of the column, and was fashioned by casting a steel tube in the column so =
that
the tube was the tennon and extended up the column a few feet, maybe even
to the height of the walls.  If there was enough movement to cause a shear
cracking condition, would it cause the crack to extend up the column along
the tube steel and then begin to fan out where the tube stops?

Just some thoughts that came to me as I read.

Take Care,
Lloyd

BTW, is this building in an area where it experienced any sudden forces,
like from an earthquake or nearby explosion?


On 5 Jan 2010 at 12:45, Rich Lewis wrote:


I have a two story precast concrete building that is experiencing some c=
racking problems. I
think I know the cause, but the types of cracks I=B4m observing are a li=
ttle puzzling. I do not have
drawings of the original building design.

There is a row of precast concrete columns along an exterior wall that h=
ave several vertical
cracks at the base. There are short precast and cast-in-place concrete w=
all panel between the
columns, about 4 feet high, at ground level. The wall cladding above thi=
s wall is primarily
insulated metal wall panels, except at one end of the building there are=
precast concrete walls
up to two story height. The short walls are creating a fixed condition i=
n the column at the top
of the top of the wall.

The precast columns are 24 inches square. The cracks are primarily verti=
cal, although they tend
to work their way to the edge of a column. They are not 45 degree cracks=
. They start at the
bottom and slowly creep to the closest face, kind of fanning out. They a=
re closely spaced
together at the bottom and spread out as it travels up and begins exitin=
g out at the edge. The
cracks stop less than 3 feet above the concrete wall panel at the base. =
For the most part, the
entire remaining height is crack free.

I believe the problem is the short wall causing interference at the base=
. I believe one of the
influences is that the precast concrete floor and roof framing shorten d=
ue to drying shrinkage
(the building is now about 9 years old) and creep from the prestressing =
force. The spandrel
beams are exposed on the face so there could also be some temperature mo=
vement affects.
The full height concrete walls located at one end are shear walls resist=
ing the horizontal
movement, so they are pulling (or anchoring) the building frame, requiri=
ng the columns to
bend. The short wall at the base creates a resistance and there is a hig=
h shear force in the
column, creating the cracks.

What puzzles me is the cracks are more vertical then diagonal.For a shea=
r failure I would expect
more of a 30-45 degree diagonal crack, which is what I see t the top cor=
ner of one of the short
walls resisting the columns. The cracks in the column may take 3-4 feet =
of vertical height
before exiting out the edge.

I would appreciate any feedback you may be able to give regarding cracks=
in concrete columns.I
can send photos to anyone who would like to look at them.

I would love to find some pictures illustrating different types of failu=
re in concrete and
explaining the probable cause, i.e. shear, moment, etc.

I would appreciate any reference citations you could steer me to. Also, =
I would appreciate any
knowledgeable precast designer you could refer me to who has experience =
in crack
investigation.

Rich


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