Support Condition ideas or suggestions

[alphaxy]

Fellow Engineers,

I attached a pdf file of my staad model (a part only) of a treatment basin system (filter bed) with a continuous water flowing in it.

The basin is embedded on soil up to the beam (as shown). I would like to get an idea of the correct approach in its support condition using STAAD 2007 on its sides and at the bottom slab. Is it preferable or more correct to use the "foundation" option or the "fixed but" option?

Or is it preferable to have support at the bottom slab and just have the passive and active pressure effect of soil and water in load combination (does not consider support on sides for soil)?

I really appreciate your help

Regards,
Alphaxy

 

[edward1]

I have designed many precast concrete buried tanks and vaults similar to this. I used spring constants of 400 kips/ft^2 on bottom slab and at rest earth pressure and water pore pressure on outside vertical walls.

 

[alphaxy]

edward1,

have you tried using STAAD in modelling those tanks and vaults? I was only given the subgrade modulus of the bottom slab. Do you mean in your statement "I used spring constants of 400 kips/ft^2 on bottom slab and at rest earth pressure and water pore pressure on outside vertical walls." that there is no need of having support at side walls? And just have loads (earth pressure and water pore pressure) to be manipulated in load combination (considering earth pressure with empty condition and earth pressure with operating condition)?

 

[edward1]

Yes

 

[alphaxy]

can you give me a sample? Or if not, what did you use in support condition? foundation option or fixed but option? Is your load analysis of earthquake based on mononobe okabe analysis?

I have lots of questions so bear with me..=)

 

[edward1]

I generally used Fixed But Mx My Mz Kfx 200 Kfy 400 Kfz 200 and was not in high earthquake zone.