cantilever column shifted 2

[NADOR123]

Hi Everyone

I am working on a problem of concrete column ( 12"x12") in a wastewater treatment plant tank. The column is a cantilever type and wooden baffles are installed between the column and the tanks wall inside vertical steel channels attached to the column and the wall . Due to lateral forces (most likely) during the water frozen in the tank, the column has been tilted and as a result shifted at the top about 12". The column is about 18' long.
Any suggestion of fixing this problem.

 

[msquared48]

Sounds like you need a removeable tie at the top of the column to limit the spreading, and some means of controlling the icing - like heat tape?

Mike McCann
MMC Engineering

 

[JedClampett]

I wouldn't fix it. It's just there to support baffles. and they will act very baffle like even with the shift. Keep an eye on it over time and see if it gets worse. Because fixing it will involve either horsing it back into place or taking it out and building a new column. And I suspect you don't want to do either of those.

 

[msquared48]

Jed:

It's going to have to be fixed as I see it, or, when the ice thaws, the baffles will no longer be supported. presently, the ice is literally holdiong the structure together, as well as forcing it apart. The icing must be controlled.

Mike McCann
MMC Engineering

 

[JedClampett]

If it spread apart, you're right, but I thought it might have deflected perpendicular to the baffles.

 

[msquared48]

Good point. I guess that I tend to think in one direction. Maybe it's a combination...

And the answer is...NADOR123?

Mike McCann
MMC Engineering

 

[NADOR123]

I was thinking of enlraging the first 4 feet by 6 inches in each direction at the bottom after horsing it back into place. But I still not sure if horsing it back would work and what is the best way to horsing it without causing more damage.

 

[JStructsteel]

If I read this, the column didnt deflect, but rotated at the base? I would use a raker system to push it back, then perhaps some braces, support perpendicular to the baffles.

 

[kslee1000]

I am lost here. a cantilever concrete column implies the base is fixed. If ther is 12" deflection on the top, don't you have problem below?

 

[NADOR123]

The only visual damage is spalled concrete all the way at the bottom of the column but there is no major damage along the hieght of the column. The column has been shifted 12" perpendicular to the baffles.

 

[NADOR123]

The tank is empty now and no further movement has observed since the top of column shift ( 12") at the begining. but it is deflected at the topwith concrete damage all the way at the bottom.

 

[kslee1000]

I don't know your reinforcing detail. But for a 12"x12" concrete column to deflect 12", the force is considerable large. Simply to push it back straight might do more harm than good (causing the concrete core to crash). I suggest to demo the column and keep the dowels intact, rebuid with proper upper braces (perpendicular to baffle).

 

[JedClampett]

If there's damage at the base, it makes sense as that's the location of maximum moment (and shear for that matter). What you call spalled concrete, I would call a compressive failure.
You could straighten the column and patch the spalling (and any new spalling from the straightening) or replace the column. Any repair would be susceptable to delaminating and allowing water to get to the bars and starting corrosion. Or you could replace the column.
I would explain the drawbacks of fixing the column (possible future corrosion at base) to whomever is paying the bills and let them decide.

 

[kslee1000]

You can estimate the column force required to move 12" by concentrate load on cantilever, after fool around a little, F = E/4*L^3 (E in ksf, L in ft). For a 10' tall column, I got F = 130 kips (assume fc'=4 ksi). Check me on this.