circular raft design

[Okey1]

I am designing a raft foundation for a 10m diameter by 7m high tank. can any one point me in the right diresction with regards to books or literature on circular raft foundation designs

Thanks

 

[JoshPlumSE]

In my experience they are usually designed as octagonal mats rather than circular. It's just easier formwork and such.

Section 9-5 of Foundation Analysis and Design by Joseph Bowles has an example of this type of footing. They do most of their analysis and design assuming an "equivalent" square foundation. But, in my experience that is typical design practice.

 

[JStephen]

In my experience, they are usually circular.

Pick a cross section, sum moments and forces about the cross section. A table of integrals is handy.

 

[dgkhan]

It will not work fully unless you want to buy it for 88$. I used it as reference to set up spread sheet when later on I was give SAP and I modelled ftg in it then.

 

[JStephen]

Note that with a tank, the tank loads are distributed across the slab as well, and that has to be taken into account.

With a tank of the dimensions mentioned, there probably won't be any uplift unless seismic loads are very high, and that simplies the calculations considerably.

 

[lexim]

Hi Okey1,

As per books and references you could also read up design principles in "foundation design' by Tezaghi and Peck. Bowles Joseph also has a discussion on the Bossineq method too.

From experience I want to advice that you model this in some structural analysis program if you got access to one and pay a good attention to the steel detailing at the corners and the centre, stresses are critical here.

Lexim

 

[BAretired]

I think you need to provide a little more information.

Where will the tank be built? What is the depth of frost penetration? What will the tank hold...water, oil or other?

Is the tank made of concrete or steel?

Is it entirely above grade or partially buried? Is there likely to be groundwater higher than the raft?

Is the roof clear spanning or will you have interior columns?



BA

 

[msquared48]

Make sure the contractor won't be tanked when he builds it.

Mike McCann
MMC Engineering

 

[Okey1]

The tank will hold water and is a steel tank which is designed according to API 650. the roof is clear spanning and there is no danger of frost or ground water effect on site.

Okey1

 

[BAretired]

This type of problem was discussed on another forum recently at:

http://www.eng-tips.com/viewthread.cfm?qid=243203&page=2

A very useful reference was provided by AeolianTexan toward the end of the thread which you may find as illuminating as I did.

BA