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Modelling soil in Staad

 
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sahilmujawar
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Joined: 17 Mar 2012
Posts: 118

PostPosted: Wed Apr 04, 2012 2:07 pm    Post subject: Modelling soil in Staad Reply with quote

dear Sefians,
Does anybody share information on how to model exact/approximate soil conditions for founation of site in staad.
Regards,
sahil mujawar
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VPandya
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Joined: 09 Nov 2009
Posts: 671
Location: Ahmedabad

PostPosted: Wed Apr 04, 2012 3:50 pm    Post subject: USE SPRING ELEMENTS OF STAAD TO MODEL SOIL. Reply with quote

Dear  Sefin,

Soil in STAAD/PRO is modeled in two ways:

1)  Spring Elements called Winkler Springs or Modulus Of Sugrade Reactions in
      Foundation Text Books. You add a Soil Spring element at Every Node of
      your  GRADE  BEAM Model or  PLATE and SHELL  Element  for a RAFT or MAT
      Foundation Model. Values of  Winkler Springs or Modulus  of Subgrade Reaction
     comes  from Soil-Consultant by Load Tests. Units of Soil Springs are in PCI or
     Pounds  Per Cubic Inch. Some text books on Foundation also give Soil Spring
     values for different types of Soils but I prefer to use Soil-Report values as they are
    based on actual site conditions and Load Tests.
2) You can also model Soil in STAAD/PRO using PLATE and SHELL ELEMENT of
     STAAD/PRO but this  hardly ever done as defining  properties of Soil Plate Element
     is not easy Soil  being a Non-Linear material.

  I recommend you use Spring Elements for Soil using Soil Consultant values. There is in STAAD/PRO a very fast way of generating all the Soil Spring Elements of your Computer Model.

Regards.

Vasudeo Pandya  P.E. ; S.E.
Structural Engineer


Last edited by VPandya on Thu Apr 05, 2012 5:16 am; edited 1 time in total
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sahilmujawar
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Joined: 17 Mar 2012
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PostPosted: Wed Apr 04, 2012 3:59 pm    Post subject: Reply with quote

Dear Mr.VPandya
,
Do you have any staad model on this so that it can help me.
Regards,
Sahil Mujawar
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VPandya
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PostPosted: Thu Apr 05, 2012 5:31 am    Post subject: STAAD.PRO V8i . Technical Reference Manual Page 380-384, Reply with quote

Dear Mr. Sahil Mujawar,

Yes there are examples of Modeling Soil in STAAD/PRO. See the following:
1)  STAAD.PRO V8i . Technical Reference Manual Page 380-384, Section 5.27.3
     Automatic Spring Support Generator for Foundations.  
2) If you  also have access to  STAAD.foundation V8i.  Section 7.2 page 353-358.  
     This is a Complete MAT (RAFT) Foundation example.

These two references should serve your purpose.  

Regards.

Vasudeoo Pandya P.E. ; S.E.
Structural Engineer
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prof.arc
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PostPosted: Fri Apr 06, 2012 12:11 am    Post subject: USE SPRING ELEMENTS OF STAAD TO MODEL SOIL. <edited> Reply with quote

if soil is to be represented by a set of 6 soil springs [6 dof per node], i would prefer that
one uses formulae recommended in the book by richart, hall and woods
or even better in the papers of  Berudugo and Novak as it also takes care of embedded footings
shear wave velocity is a better representation of soil rather than modulus of sub-grade reaction



ARC


On Thu, Apr 5, 2012 at 10:46 AM, VPandya <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
     
[edited]
     Dear Sefin,

Soil in STAAD/PRO is modeled in two ways:

1) Spring Elements called Winkler Springs or Modulus Of Sugrade Reactions in
      Foundation Text Books. You add a Soil Spring element at Every Node of
      your GRADE BEAM Model or PLATE and SHELL Element for a RAFT or MAT
      Foundation Model. Values of Winkler Springs or Modulus of Subgrade Reaction
     comes from Soil-Consultant by Load Tests. Units of Soil Springs are in PCI or
     Pounds Per Cubic Inch. Some text books on Foundation also give Soil Spring
     values for different types of Soils but I prefer to use Soil-Report values as they are
based on actual site conditions and Load Tests.
2) You can also model Soil in STAAD/PRO using PLATE and SHELL ELEMENT of
     STAAD/PRO but this hardly ever done as defining properties of Soil Plate Element
     is not easy Soil being a Non-Linear material.

I recommend you use Spring Elements for Soil using Soil Consultant values. There is in STAAD/PRO a very fast way of generating all the Soil Spring Elements of your Computer Model.

Regards.

Vasudeo Pandya P.E. ; S.E.
 Structural Engineer



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VPandya
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PostPosted: Sat Apr 07, 2012 2:04 pm    Post subject: THREE ACI STANDARDS ON FOUND. ARE USED BY USA ENGRS. Reply with quote

Dear Prof.  Arc,
Thanks for the comments. I list here following three Industry Standards used in USA. I have used first two and I think 90% of Foundation Design for STATIC LOADS in USA follows the first two. I have myself done a good number of LARGE and THICK MAT (RAFT) Foundation design using the first two. Actually my MAT (RAFT) Foundation design first went through, in-depth  In- Hose Design Review and then to get constrction permit from the City Building Inspection Department (San Francisco, and Bakerfield, CA and Chicago, IL.) my Foundation Design, Drawings were again checked and I got the required Construction Permit.  

Here are three INDUSTRY STANDARDS from ACI USA:
1) 336.2R-88 (Reapproved  2002). Suggested Analysis and Design Procedures for Combine Footings and Mats.

   Based on Modulus of Subgrade Reactions obtained by ASTM Load Test and adjusted for factors in this document.

2)   351.2R-10 Report on Foundations for Static Equipment
Totally based on Modulus of Subgrade Reactions obtained by ASTM Load test and adjusted for factors in this ACI 336.2R-88.
3)
351.3R-04: Foundations for Dynamic Equipment (Reapproved 2011)
  I thinks your comments about 6  D.O.F. soil springs based on book by richart, hall and woods fits in here and not for typical STATIC LOAD Cases.
About taking care of  LATERAL LOADS on FOUNDATION , I use
Lateral Resistance of Mat =  DLx Coeff. Friction  +  Passive Pressure Resistance on the  Thickness x Length of Mat in the direction of  Lateral  Load.
This Lateral Resistance Rh = 1.5xTotal Lateral Load (1.5 is Factor of Safety) .
Some times we have to add Grade Beams below the Bottom of Mat surface to get the required  lateral resistance by Passive Pressure.
     

I think based on first two Industry Standards from ACI, using Modulus of  Subgrade Reactions for Foundation Design is Good Enough.

We use Shear Vave Velocity and Standard Penetration Number N to define SITE CLASS required in  Code IBC 2006/ASCE 7-05.  This Site Class is used to determine SDC or Seismic Design Category of  IBC 2006 Code.  For SDC  A through D we can use
EQ. STATIC METHOD  for Seismic Design. For SDC  "E" and "F" we can not use
EQ. STATIC METOD for Seismic Design. We have to use  RESPONSE  SPECTRUM METHOD using SITE SPECTRA. Also we have to do expensive Seismic
detailing for both Steel and Concrete Structures for such SDC.

  
I agree with you that "SHEAR  VAVE VELOCITY"  number  is important to define
type  of  Soil  or  SITE CLASS  of   IBC 2006.

Regards.
  
Vasudeo Pandya  



Last edited by VPandya on Sun Apr 08, 2012 5:40 am; edited 3 times in total
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sahilmujawar
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PostPosted: Sat Apr 07, 2012 4:11 pm    Post subject: Reply with quote

Sir,
Do you have any information regarding Indian code and indian soil conditions.
Regards,
Sahil Mujawar
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arunkashikar
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Joined: 14 Oct 2008
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PostPosted: Mon Apr 09, 2012 1:08 pm    Post subject: Modelling soil in Staad Reply with quote

ASCE-4 also gives formulae for calculating soil springs bases on shear wave velocity


Regards,

Arun Kashikar


From: prof.arc [mailto:forum@sefindia.org]
Sent: 06 April 2012 11:03
To: general@sefindia.org
Subject: [SEFI] Re: Modelling soil in Staad



if soil is to be represented by a set of 6 soil springs [6 dof per node], i would prefer that
one uses formulae recommended in the book by richart, hall and woods
or even better in the papers of Berudugo and Novak as it also takes care of embedded footings
shear wave velocity is a better representation of soil rather than modulus of sub-grade reaction



ARC


On Thu, Apr 5, 2012 at 10:46 AM, VPandya forum@sefindia.org (forum@sefindia.org))> wrote:      
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