Expansion Joints Spacing

[Rorythorncliff]

I am designing an underground concrete water retaining reservoir. It is a concrete rectangle box with concrete roof(54m long x 30m wide x 5m tall). This concrete structure will be backfilled with a 300mm cover on its top roof.

My question is whether an expansion joint is required in the middle at 27m location. I have searched quite a lot resources. It is the designer decision. Only India code says maximum expansion joint spacing is 45m.

Your answer is highly appreciated!

 

[JedClampett]

You're right, no one will tell you exactly when joints are required. But they'll tell you afterwards you did it wrong.
177 ft is right on the edge of what requires an expansion joint. I wouldn't put any in in your situation. The structure is buried, which should mitigate any temperature delta and the soil acts as a restraint on movement.
EJ's are a pain. Contractors hate them. They're more prone to leakage. They need to be well caulked to do any good and contractors hate that, too.
Use a good quality mix and don't skimp on the reinforcing. I'd use .006 reinforcing ratio, especially in the long direction.

 

[Rorythorncliff]

JedClampett,
Thank you for your comments.
Based on PCA (1982), 200 ft maximum building length without expansion joints. This structure is right on the edge.
You brought two very good points. This structure is buried and soil acts as a restraint on movement.
It seems in this situation construction joints and control joints shall be good enough. Of course, adequate floor reinforcement shall be considered.

 

[ChipB]

Rory,
I try to specify Xypex admixture for my concrete structures used for containment. It crystalizes in the crack to maintain water-tightness.

http://www.xypex.com

No affiliation with them, what-so-ever.
Hope this helps,
Chip

 

[Rorythorncliff]

Chip,

XYPEX is already in agenda.

I talked to the contractor when I was doing another reservoir. The contractor said Krystol T1 and Krystol T2 are also good concrete waterproofing surface material, especially for crack repair.

Thanks,

Rory

 

[JedClampett]

I would leave out control joints, too, unless the reinforcing passes through them.
Pour in 25 ft long sections. Pour the slab in a checkerboard and wait 7 days between adjacent pours. Same for the walls.
As far as Xypex, Kristol, etc., I would rather have good concrete and waterstops rather thna some magic elixer.

 

[FootNMouth]

Have you checked out ACI 350 (Code Requirements for Environmental Engineering Concrete Structures). I have used this for spacing of control joints in retaining walls. I am not sure if they will have what you are looking for.

 

[dik]

I'd put 2 joints in the length and 1 joint in the width and use bentonite rod for a waterstop... I'd also use approx 0.5% min rfg.

Dik

 

[hokie66]

Are we talking about the floor or the roof? Whichever, I wouldn't have any joints unless you can't place that much in a day. Agree with Jed on the .006Ag reinforcement and the good concreting practice and not bothering with the Xypex stuff.

 

[rowingengineer]

Agree with Jed

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[Rorythorncliff]

This is a concrete box structure. Floor and roof have the same size, slightly different thickness.

Based on my experience in previous reservoir design and construction, the concrete cracks are not very unusual in wall due to the contractor's workmanship, curing condition, maybe early removal of formwork. During water leakage test, there are always some wet spots. As an additional protection, Xypex is an option.

Considering the contractor's capacity of pouring concrete, maybe 3 construction joints at 18m spacing in longitudinal direction, 0,1,or 2 construction joints in transverse direction (30m). I agreed with Jed, even adding control joints, the reinforcement shall not be reduced. Those joints can be cut in 1" depth and are for surface crack control purpose only (for a good appearance).

There are quite a few controversies debate about checkerboard or long strip pouring method. Maybe we can leave this option to the contractor.

 

[hokie66]

I don't see any benefit in sawcutting. You are just trying to make cracks straight. Is there an aesthetic reason for this in the floor of a tank?

When you look at the Xypex specifications, they require reinforcement, curing, etc. just as if the Xypex weren't there. The Xypex does tend to fill cracks after they form, but has no function in preventing them. Natural autogeneous healing does the same thing, just not quite as quickly.

You can't joint the roof in the same manner as the floor, so why do it in the floor?