Structural - Connecting new footing to old footing

[Asitha Aboobacker]

We are looking at installing a new steel gravity column and footing for a G+2 office building very adjacent to an existing G+1 office building. The issue we have is that on of our column footing is coming directly over the edge of the existing footing. We are looking at over pouring the new foundation over the existing. The level difference between the bottom of new and top of old footing is around 350 mm. Can anyone suggest how to sort this issue??

 

[msquared48]

I would not allow the new to bear on the old.

I would add Styrofoam over the old footing and enlarge the new to the inside if I understan the situation correctly.

Mike McCann, PE, SE (WA)

 

[oldestguy]

Without knowing the allowable bearing capacity of the soil, no way to answer.

 

[WARose]

A pic (to give an idea as to where everything is relative to each other would help), however it's usually only after about 2 feet of fill that I consider a load spreading out in the soil. If it is directly over it......and you have to have it......you need to superimpose some load on top of the existing footing. (By the criteria I mentioned.)

 

[msquared48]

Do not add any load to the existing footing.

Thicken the new footing as required to avoid that.

Mike McCann, PE, SE (WA)

 

[WARose]

Do not add any load to the existing footing.

Thicken the new footing as required to avoid that.

That sounds like a plan. (Especially if there is no info/different owners for the existing footing.)

 

[jike]

It would certainly help to know the loads (both of the wall and the new column). What is the allowable soil bearing pressure?

Generally, we like to keep the bearing of adjacent footings at the same elevation unless you underpin one footing to keep them at the same elevation. The top of the footing is generally unimportant as long as it is below the bottom of the slab. Another option is to cantilever a beam over a footing to the wall. Anchor the far end of the cantilever to another column footing.

 

[Asitha Aboobacker]

Thanks for your valuable comments. Attached below the required sketch of the footing layout.
Allowable bearing capacity considered is 110 kN/M2.
The thickness of existing footing is 400 mm.