Monolithic Concrete Tanks.

[sdz]

I have been asked to design a large, 44m dia, concrete tank using monolithic construction, i.e. no joints in the floor or walls. I understand that high reinforcement ratios will be required to control cracking.
Does anyone know of useful references for designing tanks like this?

 

[Ingenuity]

sdz,

What is its use? Water, grain, cement, other?

What is its height?

How will it be constructed...slipforming to achieve monolithic requirement.

Have you considered post-tensioning?

ACI has several documents on circular tank design.

 

[sdz]

It will be used as a water reservoir. Therefore tight crack control to prevent leaks.
No post tensioning, reinforced only.
Shrinkage compensated concrete may be considered.
Walls will be several meters high, formed in a number of lifts. There can be construction joints but no dowelled or keyed joints.

 

[mlm54]

Check the PCA(Portland Cement Association) document titled, "Circular Concrete Tanks Without Prestressing"

 

[jheidt2543]

Another thougtht to consider is that you want your final design to be constructable. By that I mean, that the details are easy to form, that clearances around rebar are large enough to allow concrete to flow easily and area contractors have the equipment necessary to built it economically. I would suggest talking over your preliminary design and details with local contractors that might be bidding the job, before you start the final design. They can offer many helpful ideas on construction details that can keep costs in line while preserving your structural requirements. They can also address issues that may affect the equipment used to build the tank.

By the way, why a monolithic tank? It may not be the most economical or serviceable in all situations.

Just some thoughts to consider.

 

[sdz]

By the way, why a monolithic tank?
The current thinking seems to be that it is better to build a monolithic structure and save on problems with joints, even though the reinforcement will be a lot higher. So I've been told.

I will have a look at "Circular Concrete Tanks Without Prestressing".

Thanks for your help.

 

[JedClampett]

I don't think your client will have a problem-free tank with a monolithic pour. We try to limit wall pours of round tanks to the 30 ft. that PCA recommends.
If you are having problems with joints, the contractors are not doing them correctly. Our company designs may round concrete structures every year and leakage is not an issue.
If the client will not budge on this, I'd document it as well as possible for future reference. I'd also make sure to have a section on epoxy injection of concrete cracks in the contract documents.

 

[BRIS]

Current thinking for rectangukar water tanks is that it is better to have monolithic construction rather than movement joints. With joints it is usual to also provide underdrainage to identify the inevitable leaks. Over the past 5 years I have seen several leading consultants argue in favour and against and it is really preference engineering. At the moment. Nevertheless, most large tanks I have been involved with in the Middle East in recent years have been designed without movement joints.

The reinforcement needs to be sufficient to limit shrinkage cracking to 0.1mm.

The theory is very simple
The tensile strength of the reinforcement must equal the tensile strength of the immature concrete so that when the concrete cracks on drying the reinforcement carries the same load as the concrete can exert in tension due to shrinkage.

The crack width is dependent on the crack spacing. And if you consider that the reinforcement is carrying full tension at the crack and zero tension at mid way between the cracks the it is apparent that the crack spacing will be twice the bond length.

The simple answer is you need small diameter bars (which have a shorter bond length) at close spacing to limit the crack width.

British Standard 8007 for water retaining structures is what we use

The minimum of reinforcement = BxD x fct/fy

Fct = strength of the immature concrete in tension.

Fy = strength of the steel

The crack spacing S= fct/fb x bar dia/2xp

P = ratio of steel area to concrete area

Fct/fb = ratio of tensile strength of the immature concrete/to bond strength (Usually about 2/3).