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[sarfaraj.husain]

not necessary......but some special structures like cement/clinker/coal (& other type)silos,chimney are supported on raft foundation due to its requirement irrespective of soil capacity....


sarfraj


[SEFI] Re: RAFT Foundation
prof.arc to: general  01/11/11 06:02 AM

Please respond to general  





A food for thought !!

Is a raft necessary on Hard Soil ?
I thought Raft / Piles are used when soil is iffy to support footings of columns
in that case, raft may have to be designed as a plate resting on flexible soil
ARC

On Sun, Jan 9, 2011 at 5:00 PM, lele_raj forum@sefindia.org)> wrote:   :  I partially with Indrajit. Raft footing on soft, low BC soil is normally designed as beams on elastic foundation. But for hard, high BC soil, soil deformations are normally minimal and do not impact on the behavior of raft footing under load. In such a case, raft footing can be considered as "rigid". I've heard, but neither practised, nor read in the literature, of a raft footing on a hard rock strata being treated as an elastic plate.








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Posted via Email

[rg.gupta]

Mr barua
I am sorry for your comments made in your recent  posting on raft foundation without any background for making such a comment i.e ' Treating a raft foundation as rigid is not only wrong but is also dangerous' In my tenure in CDO for more than 20 years in DDA where I have designed more than 100 Projects of  Group Housing of DDA mostly Load Bearing Structures upto 4 storyed
In some of the projects I have to provide raft as rigid foundation using working stress method where the other foundations options such as isolated footings ,combined footings and strip footings were not found to be feasible due to very low SBC .There is no
distress noticed or reported in these structures till today.
I have also designed foundations as flexible raft in the case of nos of framed structures for more than 5 storyed.
r.g.gupta

[prof.arc]

i agree that in several cases, even on hard soil, a raft type footing may result as default.  
in case of elevated circular water towers, we use annular circular raft.

also, wherever the columns are closely spaced, the individual footings may overlap resulting in strip footings
for design purposes, on hard soil, mostly such footings are deemed to be fixed at base


ARC



On Tue, Jan 11, 2011 at 12:00 PM, sarfaraj.husain <forum@sefindia.org (forum@sefindia.org)> wrote:

[someshwar ganti]

Gentelmen
I require professional service to help me rectify error in staad input file of a tank like structure modeled in staad as fem elements

The error is foundation of the raft of the structure, i have to give a raft foundation due to client requirements rather than due to low SBC


I will require a professional service to resolve errors and warnings in the model, check the load combination and earthquake analysis parameters of staad input file

This will be on payment basis, anyone who is interested should be well versed in fem modeling in staad

Contact me at someshwarganti@gmail.com with Ur phone number i will call and discuss in detail both issue and financial terms

Somesh