www.sefindia.org

STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

 Forum SubscriptionsSubscriptions DigestDigest Preferences   FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups  RegisterRegister FAQSecurity Tips FAQDonate
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log in to websiteLog in to websiteLog in to websiteLog in to forum 
Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.

Soil-pile-structure interaction
Goto page Previous  1, 2
 
This forum is locked: you cannot post, reply to, or edit topics.This topic is locked: you cannot edit posts or make replies. Thank Post    www.sefindia.org Forum Index -> E-Conference on Tall Buildings
View previous topic :: View next topic  
Author Message
picajol
...
...


Joined: 29 Mar 2012
Posts: 66

PostPosted: Thu Nov 29, 2012 7:35 am    Post subject: Reply with quote

Dear jshula, how is this different from STAAD AND SAFE programswhere the yuse K modulus (wich I still have problems understanding)
Back to top
View user's profile Send private message
gautam chattopadhyay
...
...


Joined: 17 Feb 2009
Posts: 129

PostPosted: Thu Nov 29, 2012 8:55 am    Post subject: Soil-pile-structure interaction Reply with quote

Is FEM applicable to soil? Is the assumption that material should be homogeneous and isotropic valid in case of soil? How to determine modulus of subgrade reaction in horizontal direction which is needed for piles subjected to horizontal forces due to earthquake and wind?

On Tue, Nov 27, 2012 at 8:40 AM, Econf_Moderator <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Forwarded message....


*********

My replies provided between **   **   below.  

Thanks.  
Jaydeep Wagh


Geotech Consultant




     
     Piled rafts are often used for tall buildings. I would request seniors to clarify some doubts that I have faced when proposing pile groups:

Today every large structure is analysed and designed using stiffness method programs with detailed study by FEA where appropriate. However, only specialised consultants are carrying out the analysis of piles/ pile groups in realistic geotechnical FE models. This leads to the following questions:


1. How is the pile-soil interface modelled in these geotechnical models?  
**The pile soil interface strength can be reduced in FEM software Plaxis by specifying the interface strength reduction factor. **

2. Is it possible to use pile stiffness calculated from geotechnical models in analysis of the foundation raft and superstructure?  
**The pile stiffness calculated from geotechnical models or analysis is used for further structural analysis of foundation raft by structural engineers FEM software (eg. Safe).**

3. Is it possible to model the interaction between different piles in a pile group and between the pile cap/ soil and piles? 
** The interaction between piles can be manually calculated by charts available for pile group action in most geotechnical books.  These charts are typically provided for uniformly or evenly spaced piles and uniform loading on piles.  The interaction between piles and pile cap can be analyzed manually by methods provided in "Pile Design" by H. Poulos.  Manual calculations may become highly tedious to use for multi layered soil profile and/or for complex loading conditions or for non-uniform pile layouts.  As mentioned in "Pile Design" also, finite element softwares provide a more accurate tool for modeling the interaction between different piles in a pile group and between piles/pile caps.    **
     



     



Posted via Email
Back to top
View user's profile Send private message
jshukla
Progressive Member
Progressive Member


Joined: 16 Jun 2008
Posts: 45

PostPosted: Thu Nov 29, 2012 3:23 pm    Post subject: Reply with quote

Dear Mr. chattopadhyay,

Is FEM applicable to soil?
Yes it is .. indeed it has reached to a confidence level by which it is possible to predict the displacement even in very complex geometry and complex soil structure interaction problems. PLAXIS, CRISP, ZSOIL, ABACUS, ANSYS are examples.


Is the assumption that material should be homogeneous and isotropic valid in case of soil?


Not necessary since those assumptions are required for elastic analysis but soil essentially involves plastic behavior. Classical example is Mohr-Coulomb model which is Elastic-perfectly plastic model for soil. Layered soil represents anisotropic and some material models are capable of handling those kind of problems.


How to determine modulus of subgrade reaction in horizontal direction which is needed for piles subjected to horizontal forces due to earthquake and wind?

If you are using FEM package no need to determine 'subgrade reaction modulus' since it is one of the way to idealize soil behavior to incorporate soil behavior in structural package. However, it is approximate method and sensitive to many parameters.

i hope it helps.

jay
Back to top
View user's profile Send private message
picajol
...
...


Joined: 29 Mar 2012
Posts: 66

PostPosted: Thu Nov 29, 2012 3:51 pm    Post subject: Reply with quote

One question on subgrade modulus of soil.
Please answer it as YES or NO.

Two foundation are of different sizes but with the same soil under them.

K factor will be different for these two foundations.

Is this correct statement?
Back to top
View user's profile Send private message
jshukla
Progressive Member
Progressive Member


Joined: 16 Jun 2008
Posts: 45

PostPosted: Thu Nov 29, 2012 4:20 pm    Post subject: Reply with quote

I acknowledge your anxiety for the question...

Yes it should be... since the size of foundation is different hence extent of soil straining is different. However if you say 2m wide and 2.5 m wide it wont have much different... but yes 10m wide raft and 2m wide footing.. I would recommend to analyze with different k-value. Please remember k-value is not fundamental property of soil. i.e. one foundation sits at 2m depth and your raft sits at 4m below ground.

I hope it helps.

jay
Back to top
View user's profile Send private message
picajol
...
...


Joined: 29 Mar 2012
Posts: 66

PostPosted: Thu Nov 29, 2012 5:37 pm    Post subject: Reply with quote

Inded, becasue of this K cannot be looked as a soil property.
Back to top
View user's profile Send private message
jshukla
Progressive Member
Progressive Member


Joined: 16 Jun 2008
Posts: 45

PostPosted: Mon Dec 03, 2012 6:22 am    Post subject: Reply with quote

Dear Colleagues,

Please attached article regarding pile group settlement estimation. Pile group interaction factors are also included in the paper.

I hope it helps.

jay



Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.
Pile Group Settlement Estimation Harry Poulos.pdf
 Description:
Pile Group Settlement Estimation – Research To Practice - Harry Poulos

Download
 Filename:  Pile Group Settlement Estimation Harry Poulos.pdf
 Filesize:  180.15 KB
 Downloaded:  1151 Time(s)

Back to top
View user's profile Send private message
Sorabh.Gupta
SEFI Member
SEFI Member


Joined: 29 Jun 2012
Posts: 7
Location: New Delhi

PostPosted: Tue Dec 04, 2012 5:23 am    Post subject: Reply with quote

Agreed. The k-value is not an intrinsic soil property at all, since it depends on the loading conditions (size of footing, depth of footing, etc.).  In fact, it is more of a mathematical ploy / parameter, used for simplified analysis of a complicated material (i.e. soil).  

The modulus of elasticity of soil (E), however, is a soil property, and directly proportionate to the k-value.  

picajol wrote:
Inded, becasue of this K cannot be looked as a soil property.
Back to top
View user's profile Send private message Visit poster's website
picajol
...
...


Joined: 29 Mar 2012
Posts: 66

PostPosted: Tue Dec 04, 2012 12:00 pm    Post subject: Reply with quote

Dear experts,
could you please join in debate on K modulus in this topic:
http://www.sefindia.org/forum/viewtopic.php?t=5428&start=110
Back to top
View user's profile Send private message
Display posts from previous:   
This forum is locked: you cannot post, reply to, or edit topics.This topic is locked: you cannot edit posts or make replies. Thank Post    www.sefindia.org Forum Index -> E-Conference on Tall Buildings All times are GMT
Goto page Previous  1, 2
Page 2 of 2

 

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


© 2003, 2008 SEFINDIA, Indian Domain Registration
Publishing or acceptance of an advertisement is neither a guarantee nor endorsement of the advertiser's product or service. advertisement policy