Cantilever Swimming Pool Problem

[drago8]

Dear All,

I have some enquiries regarding the design for RC swimming pool.

The situation is like this: The piles were piled as per the proposed swimming pool at the earlier construction stage. However, now the client/architect has changed the layout of the swimming pool. As a results, the swimming pool wall does not directly sit on the existing piles; making some of the portions of the swimming pool to be cantilevered. We proposed to add more piles to the cantilevered one (roughly 2.5m cantilever). However, due to budget constraint they did not allow to add more piles.

My question is, how to analyse the cantilever wall?

If piling is out of the solutions, then for me to support the RC wall, is only by using beams, correct?

Attached is the cross-section for the swimming pool for your reference.

Thanks for your input and help.

#LoveWins

 

[hokie66]

Beams or a much heavier slab. And it looks like one line of piles will be missed altogether unless you extend the beams/slab over to pick them up. This will require reanalysis of the pile loads, as the load distribution will be much different than before. Additional piling may suit the "budget restraints" better than all this additional design and structural alterations.

 

[Trillers]

Agree with Hokie. I would be wary about a cantilevered slab and wall section as shown. We have had to design the rehab of several pools with uneven settlement.
Recommend you urge the owner to invest in the piles and save a lot of headaches in the future.

 

[calvinandhobbes10]

Looking at the bottom diagram in your sketch.
Vertically cantilevered wall behaves per original design. Horizontally cantilevered beam/slab should get analyzed for the endpoint moment from the wall's lateral pressure plus the vertical load of the water weight. Rebar lap detailing is important.

Consider calling a screw pile guy if the owner is balking at the re-mobilization cost to add timber (I'm assuming they're timber) piles. Screw piles or push piers are likely the retrofit in 5 years anyway.

 

[hokie66]

Precast concrete piles, methinks.

 

[dhengr]

It never ceases to amaze me that the client or architect can change things in a way the screws up the budget, and then with a straight face and in all seriousness say that... ‘now doing it right will bust the budget.’ Why not go back to the way it was designed in the first place, and the budget will be just fine, you didn’t make the change, they did. And, you can be damn sure that in five years when things start showing up (going south), which they told you you must do to save on the budget, they will forget that they insisted on this solution, and now it is all your fault for not doing it right in the first place.

 

[BAretired]

I agree with the above comments. Add piles as required or return to the original design.

BA

 

[KootK]

My question is, how to analyse the cantilever wall?

There may be some potential so long as it can be a cantilevered wall rather than a cantilevered slab. If you share a plan drawing, we'll be happy to weigh in. In fact, you'd have a hard time preventing it.

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.

 

[BAretired]

If the piles were designed to meet the requirements of the original design, it seems unlikely they will be adequate for the cantilevered design.

BA

 

[Ingenuity]

...and I hope the owner is not wishing to do any serious lap swimming in that pool. At 15m long and only 3m wide any lap swimming will be a 'washing machine'.

 

[drago8]

Hi All,

Thanks for sharing your opinions. Attached is the layout plan,

Beams or a much heavier slab. And it looks like one line of piles will be missed altogether unless you extend the beams/slab over to pick them up. This will require reanalysis of the pile loads, as the load distribution will be much different than before.

Yeah, it surely looks like I need to extend the slab to catch the piles there.

There may be some potential so long as it can be a cantilevered wall rather than a cantilevered slab. If you share a plan drawing, we'll be happy to weigh in. In fact, you'd have a hard time preventing it.

Cantilevered wall? Do we analyse it like a deep beam method?

BAretired I agree with the above comments. Add piles as required or return to the original design.

Yeah, we are still trying to convince them to add more piles.

Looking at the bottom diagram in your sketch. Vertically cantilevered wall behaves per original design. Horizontally cantilevered beam/slab should get analyzed for the endpoint moment from the wall's lateral pressure plus the vertical load of the water weight. Rebar lap detailing is important.

Oh, noted on these.

It never ceases to amaze me that the client or architect can change things in a way the screws up the budget, and then with a straight face and in all seriousness say that... ‘now doing it right will bust the budget.’ Why not go back to the way it was designed in the first place, and the budget will be just fine, you didn’t make the change, they did. And, you can be damn sure that in five years when things start showing up (going south), which they told you you must do to save on the budget, they will forget that they insisted on this solution, and now it is all your fault for not doing it right in the first place.

I totally agree with your comment.


#LoveWins

 

[KootK]

There might yet be some potential here without extra piles. You could use the east and west pool walls as deep beams to attempt to deal with the cantilever. I suspect that your main issue would be punching shear in the base slab. Fortuitously, you've got a double row of piles right where demand would be highest. I'd recommend chipping the piles down a bit and running an east-west beam/slab thickening across each row of piles to deal with shear. Then let the numbers be your guide.

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.