circular conc. tanks 1

[connect2]

In a circular concrete tank wall horizontally reinforced to carry tension loads, 'hoop tension' ... we are looking for expansion\contraction joint details with regards to reinforcement thru the joint and joint spacing. This particular tank is 160 ft. dia. x 16 ft high wall, 12 ft of the wall is above grade. The tank carries liquid wastes and will experience seasonal temperature ranges of 40 deg. C to -35 deg. C. Look forward to comments, thanks.

 

[JedClampett]

You definitely do not want to install any expansion or contraction joints in a concrete tank. If you install a vertical expansion/contraction joint, you will stop the reinforcing and eliminate the hoop action. For a horizontal joint, there will be all kind of deflection compatibility issues.
If you mean construction joints, these may be installed at about 40 ft. circumferential dimension. For your size tank, this would be radially every 30 degrees. In a 16 ft. high wall, you do not need any horizontal construction joints.
Get "Circular Concrete Tanks Without Prestressing" from the PCA for design tables and tips.

 

[rabadd]

It's a while since I have looked at this but I don't think you should have vertical expansion / contraction joints in the wall. However it's certainly an option top place an expansion / contaction joint between the base and wall

 

[structbear]

Check ACI 350 for tank design. Joints are not required as long as you check your z factor.

 

[BarryEng]

I agree with JedClampett in regard to the use of the PCA book on tanks & also the use of one pour for a 5 m high wall. I have designed many tanks with the PCA book with no apparent problems. All tanks designed with a 'hinged base.' The wall & footing are composite with the only joint between the footing & the floor. A small footing below a wall, acts as a hinge.

When we pour the wall, we start with concrete placed in one location in the shape of an upside down V. Two gangs proceed in opposite directions taking care that the concrete is placed properly (not using the vibrators to shift concrete sideways, not allowing the concrete to 'slide down the slope' causing segregation, & ensuing that the newly placed concrete is compacted by allowing the vibrators to pass thru both the new & the old concrete). The two gangs will eventually come together so that there is not a cold joint at the junction.

In a circular wall (on the horizontal joint surface), I have never used a water bar, a shear key or a joint with sealant. Be careful with a 'stepped' wall (change of thickness) & a subsequent change of reinforcement, & with a construction joint all at the one location - that is asking for trouble.

Creasy (from UK) wrote a book on concrete tanks (in the 1960's) with details of many types of joint preparation. The joint preparation was 'as struck' (no joint preparation), exposed aggregate (after 3 hours, remove form & spray with water to expose the aggregate), & light hacking. Each type of joint was subjected to surface treatment of 'no treatment' 'joint dry' 'joint wet' 'water spray' (but NO FREE WATER) & a '12 mm layer of cement mortar.'

'As struck' efficiency varied from 30 to 50 % efficiency.
'Hacked' varied from 50 to 80 %.
'Exposed aggregate' varied from 75 to 100%.
The lowest efficiency was the 'cement mortar' preparation (it cures too rapidly resulting in a slightly porous sandwich).

We generally use a grit blasted surface (to ensure aggregate interlock), with the surface just wet (no free water).

Barry

 

[BarryEng]

I forgot to mention, temperature effects are considered in the Australian Code (AS 3735) & there have been other useful articles such as thermal effects in tanks by Prof Priestly (from NZ but now in California, I think).

Barry

 

[connect2]

BarryEng,
Could you give ref. wrt. Creasy, England??? +/- 1960's. I have;
Gray W.S., Reinforced Concrete Tanks and Reservoirs. 2nd ed. London 1948.
Slater G.S., 'Design of Circular Concrete Tanks'. ASCE 1939.
Manning G.P., 'Concrete Reservoirs and Tanks'. London 1967.

not much has changed really. These are the basis of PCA 'Circular Concrete Tanks without Prestressing'.

Yes Temperature effects are also considered in ACI 350 and have reviewed several of Priestlys contributions on thermal gradients in concrete tank walls.

 

[BarryEng]

connect2
I have those books too - this sounds like nostalgia.

Prestressed Concrete Cylindrical Tanks - L R Creasy, Contractors Record Ltd, London, UK, or John Wiley & Sons New York, USA. It was published in 1961 by The Concrete Library. Too early for ISBN numbers. Creasy developed the classic formulas for liquid load-full fixity, liquid load-pinned, gas load-full fixity etc, etc. He develops membrane coefficients that are remarkable simlilar to the PCA publication (tabulations based on Hsquared/Dt).

See also:-
* Design of liquid retaining concrete structures by R D Anchor (part of the Anchor, Hill & Hughes team for the BS code) 1981, ISBN 0-903384-24-8
* Circular storage tanks & silos by A Ghali, 1979, ISBN 0-470-26727-5 (matrix methods but with heaps of tables)
* Concrete liquid retaining structures by Green & Perkins, 1980, ISBN 0-85334-856-1

I still think that the PCA publication is the best overall publication for circular tanks.

Barry

 

[BarryEng]

connect2
I forgot to mention, from A Ghali's book, a check with the 'old' methods shows very little difference in the results using both methods.
Barry

 

[connect2]

structbear,
unless i'm mistaken 'z' factor is a function of expansion joint spacing in ACI-350-01. Which gets back to my original question of thermal gradients and tanks walls primarily above grade.