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Raft design

 
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goyallc
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Joined: 07 Nov 2008
Posts: 1

PostPosted: Tue Feb 23, 2010 5:36 am    Post subject: Raft design Reply with quote

I have modelled a raft using plate mat  in STAAD Pro and got certain values of base pressure.
After increasing the thickness of raft, keeping all other conditions like loads and supports same, the base pressure get modified and the base pressure values are less for higher thickness of raft.

I want to know, whether Safe bearing capacity should be checked against base pressure?
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Yogesh.Pisal
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Joined: 18 May 2008
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PostPosted: Thu Feb 25, 2010 11:40 am    Post subject: Reply with quote

Dear friend,

In my opinion bearing pressure should not increase. Try to send your STAAD files, so that I will check the reason for same.

You can compare bearing pressure in STAAD against Gross allowable bearing pressure.

Regards,
Yogesh Pisal
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thirumalaichettiar
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PostPosted: Thu Feb 25, 2010 1:41 pm    Post subject: Reply with quote

Hope that there is a separate program from STADD by name STAAD FOUNDATION is to be used for best results for foundation. Instead of bearing pressure use modulus of subgrade reaction for the support.

T.Rangarajan.
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ankitvaibhava
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PostPosted: Sat Jan 25, 2014 7:40 am    Post subject: Reply with quote

thirumalaichettiar wrote:
Hope that there is a separate program from STADD by name STAAD FOUNDATION is to be used for best results for foundation. Instead of bearing pressure use modulus of subgrade reaction for the support.

T.Rangarajan.



Sir My problem is that in my soil report I have only Bearing capacity and not subgrade soil modulus. So how do I use Bearing Capacity in Staad Foundation.
pls reply me at ankitvaibhava@gmail.com
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gpsarathyy
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Joined: 28 Jun 2010
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PostPosted: Sat Jan 25, 2014 6:09 pm    Post subject: Reply with quote

Dear Er. Ankit,

To use SBC in the STAAD file, you can use the following method.
SBC x area of element / allowable settlement (this will give you a spring value KN/m)
which shall be used in the STAAD as spring support.
Here the complication, based on each element size or contributing area we have to modify the spring value whereas if you use subgrade modulus, this is not required. It is taken care by software itself.

This shall be used in the absence of Subgrage modulus only. If subgrade modulus available it is easy and better to go with the subgrade modulus.

_________________
G.PARTHASARATHY M.E. CEng(UK), MICE., MIE.,
CHENNAI
GPSARATHYY@GMAIL.COM
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