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Cracks in Concrete Column

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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