Expert: Arshad Khan - 1/20/2011

Question
QUESTION: Dear Mr Arshad
I m designing a water tank for water treatment facility. The
tanks is of 60m x 103m x 7m, and it is underground.
Kindly advice me if i should provide expansion joint in base
slab and walls

Answer
Hi Ahmed,

If you had checked my past answers, you would have found the following:

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Question: Dear Mr Arshad
What is the criteria of providing expansion joints in large water tanks.



Answer: This depends on whether the tank is underground or above ground, and also on the shape- if underground then effectively you do not need any expansion joints in the floor or walls, but may need on roof if that is exposed to the sun. If above ground, you need to work out the maximum joint spacing based on the amount of rebar you include to resist early age cracking as well as crack-widths. This would vary between 7-15m.

If the tank is circular, then you cannot have any movement joints in the walls, but could have in the roof, although the norm is to have a sliding joint between the roof and the wall.

---------- FOLLOW-UP ----------

QUESTION: Dear Mr Arshad
I m designing a water tank for water treatment facility. The tanks is of 27m x 54m x 7m, and it is partially underground.
Kindly advice me if i should provide expansion joint in base slab and walls spanning 54m.

Answer: Hi,

As I explained before, you can design this with or without joints, depending on construction methods and amount of rebar you will have to detail to prevent early age and thermal cracking. Please refer to these guides:

www.ciria.org/.../ContentManagerNet/TemplateRedirect.aspx?...=/ContentManagerNet/...

www.techstreet.com/standards/BS/8007_1987?..

The more joints you incorporate, the less rebar you will need to use, but on the other hand you will spend more money on joint water-bars, etc and increase the risk of leakage due to bad workmanship.