Thank you 'atilio' for sharing your views and comments.
I think you have modified the model, can you please upload it.
Hi , I think that 15000 could be wright, this constant depends also on the geometry and dimension of the fundation, I dont Know If you use the expresion K BxB = K0,3 ((B + 0.3)/(2B))2 ;(Terzaghi, the expresion for square foundation in metric units) where B is the distance between the walls, (B = 4.85 m in your case) and K0,3 is the is the value of the modulus of the soil that you obtain by field test using a 0.30 x0.30 m plate . Finally KBXL = KBxB (1 + 0.5 B/L )/1.5 where L is the lenght of the foundation ( L = 19.40 m in your case).
Another thing is that the number of plates to represent the behavior of the fundation is very low, ( you have 5 x 5 plates) you need at least 8 x 8 plates in each tank. a quik correction will be divide each plate in four.
I hope this help you
i have to design an underground RCC 4 chamber tank, for that i have modelled it with plates = 350mm as per IS 3370.
I was comparing the results of manual calculations with staad. they are not maching.
Staad shows maximum moment at the centre (two way bulging, thats ok because the ratio = 1), but the moment works out to be maximum of 17Kn.m as per staad while it comes out about 37Kn.m manually.
Second thing i also want to know whether the suppoerts modelled are correct, as the soil is silty sand with SBC = 150 Kn/m2.
Please suggest necessay corrections, technically as well as in modeeling.
Thanks in advance.