Combined Pile Cap

[drago8]

Hello Hi,

Could anyone here guide me on how to design combined pile cap supporting two columns? The situation is due to the overlapping of pile cap of the individual column.

Thank you.

#LoveWins

 

[KootK]

A sketch of the situation would be a good place to start.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TLHS]

Depends heavily on the depth to span ratio and stiffness of the cap. If the cap is basically rigid compared to the piles and there are lots of piles then my hand method is basically:

-Solve for the pile forces based on the applied column loads
-Then I treat the pile forces as an area load/gradient on the bottom of the cap and my columns as supports to come up with my maximum moments.
- Find max shear by inspection, as well as checking for punching


As soon as it gets into something that looks like deep beam theory I go strut and tie if it's critical, especially if it's only a couple of piles, and other more straight forward deep beam approximations if a bit more safety factor can be built in.

If there's fewer piles and a less rigid cap I might go with plate theory or FEA

There are lots of ways to solve this type of problem depending on the conditions, and all of them are a little bit fiddly.

 

[drago8]

@KootK

Attached is the diagrams for the pile caps.

@TLHS

My resultant load will acting on the centroid of the pile cap still right? I need to determine shear for both the columns?

#LoveWins

 

[KootK]

Here I think that you can just allow the individual pile cap designs to blend without modification to the rebar. The portions of the cap beyond the piles really just allows for tie anchorage and you've got plenty of that. I'm assume predominantly axial load on the piles. You might see some cracking in the interstitial space so maybe a little rebar there for that.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.