Pile Cap Design with Asymmetrical Piles 1

[drago8]

Greetings to all the members,

This one is regarding the design of pile cap. As per attached PDF, we design the pile cap (for 3 piles) in a way the pile spacing is equal centre-to-center. However, due to the ground condition, one of the 3 piles cannot be piled at the proposed position, thus they piled it a bit away (~300mm away in x-dir from the original position).

Could anyone guide me on how to re-design the pile cap? Would it be better to use square pile cap instead now? What about the reinforcements? And how could I make sure the loading on the pile would now exceed their capacity?

Appreciate your help. Thanks.

#LoveWins

 

[thaidavid40]

Your column load still falls within the centers of the newly-relocated pile arrangement. I don't see where another pile would help much, and would just cost more money. Just thicken the pile cap, and design the reinforcing to take the increased moments due to the distance from the reconfigured centroid to the out-of-place pile.
Dave

Thaidavid

 

[BAretired]

First, you should determine the load on the two correctly placed piles. You may have to add a fourth pile. Label the misplaced pile A; the others, going clockwise, B and C. Pile C appears to be the worst case, assuming no base moment on the column. If the column has a moment, then even the symmetrical case will result in different loads for each pile.

Assuming no moment between column and pile cap, the load on C may be obtained from statics; it is P.e/d where P is the column load, e is the eccentricity of column from line AB and d is the shortest distance between C and line AB. The weight of pile cap must be added as well. If the load to pile C exceeds the allowable, add a fourth pile positioned to reduce the load on B and C.

BA

 

[KootK]

18" is a pretty tight pile spacing. What type of pile is being used here? One of the drawbacks of such a tight layout is that the inevitable pile misplacement will wreak havoc on your load distribution between piles.

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.

 

[drago8]

@KootK: They are using 200 SQ. RC piles.

#LoveWins

 

[drago8]

@BAretired: Thanks for your guide. Yup, I calculate the loading on the piles, both loading at Pile B and C exceeds. So I am gonna try to add another pile.

@thaidavid40: If not adding new pile, then the point would only have 2 piles in which the post required 3 piles. How do we do that without adding additional pile?

@KootK: Yeah, the pile spacing is roughly 3D..

#LoveWins

 

[Leftwow]

So how would the moved pile transfer tensile forces if it's centerlines aren't on the pilecap?

 

[KootK]

I assume that the pile cap would be enlarged. The renegade pile should still be under compression, just less than its intended share.

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.