Foundation issue

[geoffdale]

Hello all;
We have a slight situation on our hands. We have a pre-cast column attaching to a pad footing, and the pre-cast column is poured already. They contractor has set the pad footing too high by a foot, and we don't have any piers. The pad footing is rather large, approx. 14' square by 27" thick (for shear). The load is approximately 450 kips. Rather than telling our contractor to remove the footing or repour the column, we said that we will investigate making the existing siuation work. We are looking at notching out the 12" height of the footing (leaving us still 15") for the width of length of the column, and somehow trying to transfer the bulk of the load back up to the top of the footing. We have extremely solid soil directly below us as well. Has anyone ever tried tackling something like this, or should I tell the guy to do it right? Thanks for all input.

 

[apetr26542]

Are you saying he poured it a foot too thick or the whole thing is a foot too high, if you carve out a pocket in the footing you will be cutting out the top mat of rebar, if any. you would also be reducing the capacity of the footing for punching shear, also I would be concerned as to the method of removing this. I had to do some thing similar for a roof leader and allowed about 3" carved out, but much smaller load.

If left as is, would it stick out of the ground?

 

[UcfSE]

That seems like a lot of liability to assume for someone else's mistake. Taking 12" out of your footing thickness is quite a bit. Is the column large, does that reduce your "d" and "h" by 12" for a lot of the footing area? I would imagine that if you have a column large enough to work for punchign shear with a reduced "d" then you may end up with problems with flexure. The footing is one of the last things you'd ever want to fail, especially with 450k of load.

Will the higher footing be exposed above grade? Does the bottom of the footing still meet the minimum depth set forth by the geotechnical engineering report? Why can't you cut 12" out of the column length? Sawing and cutting a 12" hole into the top of a footing is going to send energy and cracks all through the concrete and may disrupt the bond with the steel as well.

 

[apetr26542]

UcfSE just gave me another thought, do you now have a frost issue if your footing is 12" too high.

 

[geoffdale]

The footing was poured 12" too high. There is no top mat of rebar. It is an interior footing, therefore frost is not an issue.

 

[azcats]

How is footing/column connection detailed? Is there any way to cut off the column work from that end instead of footing demo?

 

[geoffdale]

The pre-cast column has pre-stressed tendons in it, therefore the idea of cutting it is extensive.

 

[apetr26542]

Being this is an interior column, would not the whole footing be above the interior slab?

 

[geoffdale]

An update, we asked the pre-eng guys to re-pour the column. We all have to sleep at night

 

[civilperson]

Cutting prestressed tendons is no harder than cutting reinforcing. The price to cut and then set in non-shrink grout should be comparable to any other fix.

 

[VTPE]

Most pre-stressed items are utilize bonded reinforcing, therefore cutting the cables may not be as big a deal as in the case of unbonded cables. The cables will re-develop themselves within a couple of feet. You may want to check with the P/S manuf.