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Re: Cracks in Concrete Column

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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 bottom
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 cracking problems. I 
> think I know the cause, but the types of cracks I´m observing are a little puzzling. I do not have 
> drawings of the original building design.
> 
> There is a row of precast concrete columns along an exterior wall that have several vertical 
> cracks at the base. There are short precast and cast-in-place concrete wall panel between the 
> columns, about 4 feet high, at ground level. The wall cladding above this 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 in the column at the top 
> of the top of the wall.
> 
> The precast columns are 24 inches square. The cracks are primarily vertical, 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 are closely spaced 
> together at the bottom and spread out as it travels up and begins exiting 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 due 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 movement affects. 
> The full height concrete walls located at one end are shear walls resisting the horizontal 
> movement, so they are pulling (or anchoring) the building frame, requiring the columns to 
> bend. The short wall at the base creates a resistance and there is a high shear force in the 
> column, creating the cracks.
> 
> What puzzles me is the cracks are more vertical then diagonal.For a shear failure I would expect 
> more of a 30-45 degree diagonal crack, which is what I see t the top corner 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 failure 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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