Concrete Column Pour Issue?

[psychedomination]

Hi there, I'm working on a project, where the contractor poured a column prior to the inspection. When I was on site last, I noticed that the the cmu block wall was protruding into the column section. Before I got a chance to tell them to chip the cmu block back to facilitate the concrete pour, they had had poured the column the following day...

See below :



Albeit frustrated, I checked the column capacity with a reduced cross section, assuming that the column section was the width and depth at the bottom throughout.

On the bottom, the column section is 10" wide X 12" deep.

On the top, the column section 16" wide X 12" deep.

The column still worked fine as a 10" wide X 12" deep section in bending and axial. However, is my reduced section assumption the right approach.

As the cmu block is concrete, should I instead be considering the bottom dimension as 16" wide X 12" deep throughout. Or would it be better to stick with the more conservative assumption of 10" wide X 12" deep throughout?

the column is a two storey column supporting a transfer beam that is holding up two storeys.

 

[ANE91]

Looks like they forgot about the column and hammered out some CMU to accommodate.

CMU is not the same as cement concrete, but you know that. Moreover, CMU masonry is very much not cement concrete. The mortar is much less stiff, and the masonry behaves as a different composite than reinforced concrete.

This normally wouldn’t be a big deal, but you don’t want to take any chances with an overlying transfer beam. I certainly wouldn’t. The column isn’t huge, though, so the loads can’t be too crazy. It’s probably fine, but I’d want a load test. Half the time, contractors prefer to redo the work than go through a load test.

Things to consider: You will have stress concentrations that are difficult to account for, at the geometric nonlinearity. Further, I’d be concerned about inducing an unintentional plastic hinge where the section narrows.

 

[SWComposites]

Is it just me, or is that mortar work on the CMU walls really shoddy?

 

[psychedomination]

@ANE91 Thanks, that is helpful. This is a residential project, so the axial load on the column is quite light at 290kN, even when holding the transfer beam.

One good thing I guess is that the ground floor slab still need to be poured, which will raise the floor level by 6" and encase the column at the bottom, reducing the height of the most significant discontinuity at the very bottom to ~2"

 

[TRAK.Structural]

Are all the column vertical bars embedded into the slab? Seems a little odd to me since I don't see a lap splice on any of them in the picture which appears to show 6+ feet of height. Usually the vertical bars that come out of the foundation are pretty short.

 

[psychedomination]

@TRAK.Structural

Yes, all of the vertical bars are hooked into the concrete pad foundation below the column.

Column height is quite short for this level (~11'), the contractor just used full length rod (no laps), instead of using short starter bars and lapping with verticals.