Column landing on slab courtyard 1

[COEngineeer]

Ok, I hope I can explain this very well.

So lets say I have basement foundation wall, lets say the top of footing is at 90ft elevation. The main floor is at 100 ft. The courtyard is only 6" below the main floor and its all covered with 4" slab + stone veneer.

Lets say I have a column from a deck that lands on the courtyard. This column is only 3 ft away from the basement wall. Can I just stop this column at the courtyard level and maybe thickened the slab around the column? (It will be sitting on fill material)

OR do I need to go extra few feet for frost depth?

OR do I need to use sonatube all the way to the native material probably around 90ft elevation because it is so close to the basement foundation wall.

 

[UcfSE]

I would think you should take the column support below frost depth, but I don't live where there's snow.

As far as the load goes, you can figure the additional load on the wall and superimpose that with the regular basement load in your analysis. Das goes over at least one procedure to do this, either in Foundation Engineering or Principles of Geotechnical Engineering, I don't remember which.

 

[COEngineeer]

UcfSE, I was just thinking about how they are going to build this thing. They need to dig down to 90ft elevation for the basement. That means if you put a column pad that is only 3 ft away from the wall, you can only slope it up about 3 ft (93ft elevation).

 

[SperlingPE]

YOu don't need to excavate to level 90 for a new pad footing. You need to excavate deep enough so that the new footing does not influence the existing wall. Draw a 45 degree or 60 degree line from the corner of the new footing. This line should NOT intersect the existing wall. Place the bottom of the footing at a level where the influence line does not intersect the wall.


Or if you just want to go to frost level with the footing, the existing wall needs to be checked for the new load from the new footing.

 

[minorchord2000]

I would just modify what sperling posted: You can place your post footing where you need to, but the basement wall must be designed to resist the additinal surcharge load to the post load.

Older Bowles texts have these conditions shown and the applicable equations you can use to calculate the additional load on the basement wall system.

Sperling's suggestion is correct if you do not want the post load to impact the design of the basement wall.

 

[COEngineeer]

Thank you for your responses. It sounds like you 2 understood my question completely. I wasn't worried about the surcharge to the basement wall. I was just worried if they build the basement first, back-fill, then build the column pad (only to frost depth), the column will sit on fill material. I don't want the column to settle because it is supporting concrete topped deck plus everything is going to be covered with veneer including the column. So it sounds like I should make them excavate to around 93ft elevation (1:1 slope from the footing) for the column pad and use sonatube up to 100ft elevation, right?

 

[SperlingPE]

If you are concerned about settling, be sure that when the backfill is placed that compaction requirements are met. Now this is rarely done in residential construction in my experience, because of the expense of testing. If no testing is done and you are worried about settlement, bottom of footings should probably be placed on undisturbed soil.

If you are going to place the footing in the fill, a three foot square footing with it's centerline 3'-0" away from the wall should be placed around 91'-6".

Talk this over with your supervisor. There are always other factors specific to your project that will not be considered by persons answering questions.