L Shaped Swimming pool 1

[tclat]

Hi,

I have an L-Shaped swimmming pool. I have added a construction joint to break the pool into two separate structures because I am concerned about the re-entrant corner. One section will be 45'-0 long x 8 feet wide and the other section is 15'x15'. I am now detailing the construction joints in the slab and walls and would appreciate some comments on whether I should detail the joint as a complete contraction joint (no steel through the joint) or as a partial contraction joint with atleast 50% of the horizontal steel crossing the joint. I plan to have a waterstop at the joint and a 1"x1" min waterproofing sealant at the surface of the joint on the water side.
I am in a seismic zone (SDC D)

Thanks

 

[slickdeals]

Is this an elevated pool or a pool at ground level?
How does a construction joint break the pool into two separate structures?

 

[tclat]

Hi,

Yes. The pool is elevated. Currently I have a wall on either side of the construction joint but the walls sit on the same foundation which is a raft (mat). I meant "break" from an analysis point of view.

 

[slickdeals]

The only way you can truly "break" it is by providing an isolation joint. A construction joint won't help to make it two separate structures. There are many details to achieve full moment capacity at the re-entrant corner.

 

[hokie66]

I would build it without joints. Reinforce all corners with hairpins as shown in Fig 2: e) of the link posted by slickdeals. I would make sure of having at least 0.6% Ag reinforcement everywhere in the pool. If the pool is over an occupied area, you will need a waterproof membrane. Don't depend on sealants, as they require a lot of maintenance.

 

[tclat]

Thanks for the comments.

Is there any special detailing required for the slab at the re-entrant corner? How do you typically analyze these corners (wall and slab) without a joint? For buildings and other structures with large projections we normally recommend expansion joints to eliminate the re-entrant corner. While this pool does not particularly have a large projection, the slab seems to be a weak point in this area and any uncontrolled crack which leads to a leak or is unsightly would be a big problem. This developer prefers waterproofing admixtures over membranes.

 

[hokie66]

If your developer "prefers waterproofing admixtures over membranes" for a pool, then you have a big problem. These admixtures only work to seal cracks which are leaking. Is that what you want? There is no substitute for good design, detailing, and concreting practice.

As to your question about the reentrant corner in the slab itself (if that is your question), extra reinforcement can tend to control cracking, but not eliminate it.

If the question is about the wall to slab junction, then using the same hairpin type reinforcement detailing as for the horizontal bars is the way to go, as those U-bars are much more efficient in developing joint moments than other details.

Without more information about how the pool is supported and detailed, I am afraid that is all the advice I can offer.

 

[tclat]

thanks Hokie,

I would prefer that design and detailing which would prevent the pool from leaking in the first place. I am concerned about the re-entrant corner in the slap itself.

The pool is about 12 feet above the ground. So far, the 45' long section is supported by 4 cross walls 8' wide to match the width of the pool in this section. The perimeter walls of the pool also extend to the ground. I have the extra cross walls since there is a ground elevation difference which adds a soil pressure to overall system. I have checked doe Ko since I don't want the pool to move.

The other section of the pool is supported by its perimeter walls which extend to the ground. Where the two sections meet, I was thinking of putting a construction joint with a supporting wall on either side of the joint but wasn't sure if I should let the reinforcement run through the joint.

The pool is not over an occupied area but we don't want it to leak for other obvious reasons.

The question really is, should I let the slab crack where it wants to crack and detail that joint to prevent it from leaking or should I detail the joint so that I control the cracks enough that they don't leak. If the answer is the latter, then how much reinforcement is enough. I currently have 0.5%Ag in each direction and distributed in two layers. I understand that FEA analyses of this corner can produce hotspots are probably not realistic. So is there any practical way to analyze the corner of do you depend on detailing that thas become acceptable over the years. Grateful if you could shed some light on how you have handled situations like this.

Thanks

 

[hokie66]

How think is your slab? 8" would be my guess. At the corner, I would add some diagonal bars to control the inevitable cracking. You could place a construction joint there, centred over either of the intersecting walls. Just make sure that all the reinforcement runs through. If it were mine, I would cast it all at the same time.

Restraint cracking is probably more an issue than usual with your pool, being supported on walls which will restrain the slab from shrinking, resulting in tension and cracking of first the slab, then the pool walls. I would therefore provide extra reinforcement in the slab parallel to the walls, and in the bottom of the pool walls.

 

[gobsmacked]

This sounds like a prestressed concrete solution would hold everything together when seismic activity occurs, plus no cracks at all if properly detailed. Admittedly more expensive, but it's the right approach.

 

[DST148]

@tclat> In addition to good detailing practices at the corners, you may provide a splay / haunch on the outside of the re-entrant corner (assuming haunch is either buried or acceptable architecturally if visible). The pool walls could be square on the inside .