RC column bellow terrain?

[greznik91]

Hi guys!

I'm working on residental building as shown in image bellow.
I'd like to hear your take on RC column 250 x 250 mm:
(1) should I make column foundation/spread foundation at the same level as main structure footings or
(2) should I make a foundation higher (0,8 m bellow terrain line bellow terrain level

In case (1) RC colum is almost 6 m in height, half of that in terrain,
in case (2) RC column is 3 m in height.

In both cases the column foundation is connected to the main structure by foundation beams in both direction (because of differential settlements of column's foundation and the main structure foundations)

In case (1) column's foundation is connected by foundation beams to other foundation and in case (2) beams are connected to to RC walls.
I'm not really sure what's my take on RC column in case (2) where half of the column is in terrain - bellow ground level but I'm not fond of it. How does this work in case of seismic forces. Any special consideration?

thank you for reply!

 

[JoshPlumSE]

Is that area going to be excavated with the basement? If so, it might be easier to do the foundation at or near that same level. As opposed to back filling and then making sure the backfill is compacted to an acceptable criteria.

Alternatively, if the area is NOT excavated all the way down, then it would be better to just excavate for the column footing as far down as is necessary rather than to the same depth as the basement foundation.

I guess that's not a real answer. I'm just saying that it probably depends on your site conditions and construction plan.

 

[HTURKAK]

Hi greznik91 ,

Pls find below my opinions for your querries,



I'd like to hear your take on RC column 250 x 250 mm:
(1) should I make column foundation/spread foundation at the same level as main structure footings or
I will suggest this one but extent the basement storey so the walls .. The ftg will be wall ftg similar to main block. Your basement area will increase..If you want to provide separate ftg, the tie beams should be provided at foundation level and you will need grade beam at ground level for porch slab and to reduce the column ht.

(2) should I make a foundation higher (0,8 m bellow terrain line bellow terrain level][/quote]
You may choose this alternative ... but make sure that the ftg will rest on undisturbed soil. In this case, the tie beam will also be grade beam should be connected to the basement wall at ground level...


Good luck...

 

[Klitor]

You could cantilever an upturned rc beam and design it without column

 

[greznik91]

Thanks for replies, I'm not comfortable with a column being 6 m high at 250 x 250 mm cross section. Think Im gonna go with (2).