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.