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Regarding P-D analysis.
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rkumar
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PostPosted: Sat Jun 26, 2010 10:15 am    Post subject: Regarding P-D analysis. Reply with quote

Hello Seniours,
 
I need your guidance in this topic. When do we use P-Delta analysis, when it becomes necessary to do p-delta analysis and how to do p-delta analysis, what is its major applications, advantages and disadvantages. Upto what extent it is in use nowadays in INDIA.
 
waiting for your answers
 
with regards
 
RAKESH KUMAR
Learner


*"Please consider the environment, take a print of this copy if u really need to". Use Gently.

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coolestbliss
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PostPosted: Sun Jun 27, 2010 5:30 am    Post subject: Reply with quote

Dear Engineer,
P-Delta means P(load) x Delta(moment arm) = Moment M
If you have designed ur column on say 500 load (what ever the units are) and the column is SLENDER....now as you know
from ur previous knowlege that now column will buckle at load much less than design load 500 and when it will buckle it will
deflect by a value equals (DELTA)...now additional moment will be there in column which is equal to 500 x DELTA and due to
this extra moment for which our column was not design for will fail as compared to that of stocky column....so in order to
avoid this we can anayse slender columns in three different ways...and yes this P-DELTA is only for slender columns..
well here i will refer ACI code as i dont know about IS codes...so ACI defines three methods of analysis for slender columns:-
1-Non Linear Second Order Analysis
2-Elastic Second Order Analysis (which we commonly use in Etabs by provind frame modifiers)
3-Moment Magnification Method
but moment in compression members after any of the above analysis should not exceed 1.4 times the moment from first
order analysis....otherwise change ur section.
But Second-order effects in many structures are negligible and code says u can ignore slenderness according to ACI 10.10.1
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vikram.jeet
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PostPosted: Wed Jun 30, 2010 10:15 am    Post subject: Regarding P-D analysis. Reply with quote

P-Delta Analysis

In my opinion:

P-delta Analysis represents the determination of additional moments in a member  
due to lateral deflection(delta) as result of its buckling under (i) Axial compressive force P

(ii) Sway Forces, may also cause P delta effect but these are not allowed to exceed
in the structure system by limiting the horizontal drift

(iii) Joint displacements may also cause p-delta effects if structural proportions of
columns/beams in a frame are inadequate vis-a vis height/span respectively

Additional moments depend upon the slenderness of member .

P-delta effect is applicable to all members .However keeping in view the magnitude  
of its effect, the members are treated as Slender members or Non-slender member.
For non- slender members, the IS code has given a limit beyond which a member
is slender . In non- slender members, its effect is negligible and can be ignored
without compromising with structural safety.
However in slender members it has to be accounted and added . For structures  
like buildings , there is no need to carry rigorous P-delta analysis but formulae are  
available to determine the additional moments due to P-delta effect.

For Mega structures like Central tower of a Cable stayed bridge and similar,
the rigorous P-delta analysis is required  

Tall Structures subject to sway under the action of horizontal forces could also
suffer from the P-delta effect if delta exceeds beyond limits. Codes have
provided limitations for lateral drift for building columns /shear walls , beyond
such limitations the structural safety is at risk and shall not be exceeded.

Large joint displacements would also cause secondary moments .structural
sizing must be adequate to avoid large displacements



best regards

vikramjeet

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rkumar
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PostPosted: Fri Jul 02, 2010 4:24 am    Post subject: Regarding P-D analysis. Reply with quote

Hello Mr Vikram Jeet,
 
Thanking you sir. It was a helpful guidance from you.
 
with regards
RAKESH KUMAR


*"Please consider the environment, take a print of this copy if u really need to". Use Gently.



On Wed, Jun 30, 2010 at 5:00 PM, vikram.jeet <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  P-Delta Analysis

In my opinion:

P-delta Analysis represents the determination of additional moments in a member
due to lateral deflection(delta) as result of its buckling under (i) Axial compressive force P

(ii) Sway Forces, may also cause P delta effect but these are not allowed to exceed
in the structure system by limiting the horizontal drift

(iii) Joint displacements may also cause p-delta effects if structural proportions of
columns/beams in a frame are inadequate vis-a vis height/span respectively

Additional moments depend upon the slenderness of member .

P-delta effect is applicable to all members .However keeping in view the magnitude
of its effect, the members are treated as Slender members or Non-slender member.
For non- slender members, the IS code has given a limit beyond which a member
is slender . In non- slender members, its effect is negligible and can be ignored
without compromising with structural safety.
However in slender members it has to be accounted and added . For structures
like buildings , there is no need to carry rigorous P-delta analysis but formulae are
available to determine the additional moments due to P-delta effect.

For Mega structures like Central tower of a Cable stayed bridge and similar,
the rigorous P-delta analysis is required

Tall Structures subject to sway under the action of horizontal forces could also
suffer from the P-delta effect if delta exceeds beyond limits. Codes have
provided limitations for lateral drift for building columns /shear walls , beyond
such limitations the structural safety is at risk and shall not be exceeded.

Large joint displacements would also cause secondary moments .structural
sizing must be adequate to avoid large displacements



best regards

vikramjeet








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u.mukesh
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PostPosted: Mon Jul 05, 2010 8:40 am    Post subject: Regarding P-D analysis. Reply with quote

Hello
I disagree with Mr. Vikramjeet.

The P-delta analysis accounts for the secondary moments due to
vertical loads on deformed structure; because of presence of horizontal loads.

For example; consider a cantilever column subjected to a vertical (P) and horizontal (H) load
at the free end. If the deflection at free end due to H is delta; so the vertical load P is also
shifted by "delta" amount. So this "PX Delta" gives the secondary moment due to vertical load.

If there is no horizontal load this moment will be zero or If we do normal analysis this moment will be zero.
So P-delta analysis does not give any moment because of "Buckling". So P-delta analysis is
useful when you have horizontal loads on the system.

Regards
Mukesh Upadhyay


On Fri, Jul 2, 2010 at 10:00 AM, truenotesrakesh <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  Hello Mr Vikram Jeet,
 
Thanking you sir. It was a helpful guidance from you.
 
with regards
RAKESH KUMAR


*"Please consider the environment, take a print of this copy if u really need to". Use Gently.




On Wed, Jun 30, 2010 at 5:00 PM, vikram.jeet forum@sefindia.org (forum@sefindia.org))> wrote:
:  P-Delta Analysis

In my opinion:

P-delta Analysis represents the determination of additional moments in a member
due to lateral deflection(delta) as result of its buckling under (i) Axial compressive force P

(ii) Sway Forces, may also cause P delta effect but these are not allowed to exceed
in the structure system by limiting the horizontal drift

(iii) Joint displacements may also cause p-delta effects if structural proportions of
columns/beams in a frame are inadequate vis-a vis height/span respectively

Additional moments depend upon the slenderness of member .

P-delta effect is applicable to all members .However keeping in view the magnitude
of its effect, the members are treated as Slender members or Non-slender member.
For non- slender members, the IS code has given a limit beyond which a member
is slender . In non- slender members, its effect is negligible and can be ignored
without compromising with structural safety.
However in slender members it has to be accounted and added . For structures
like buildings , there is no need to carry rigorous P-delta analysis but formulae are
available to determine the additional moments due to P-delta effect.

For Mega structures like Central tower of a Cable stayed bridge and similar,
the rigorous P-delta analysis is required

Tall Structures subject to sway under the action of horizontal forces could also
suffer from the P-delta effect if delta exceeds beyond limits. Codes have
provided limitations for lateral drift for building columns /shear walls , beyond
such limitations the structural safety is at risk and shall not be exceeded.

Large joint displacements would also cause secondary moments .structural
sizing must be adequate to avoid large displacements



best regards

vikramjeet















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hemal
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PostPosted: Tue Jul 06, 2010 3:16 am    Post subject: Regarding P-D analysis. Reply with quote

Hello,

I agree with Mr. Mukesh Upadhyay.

Moments due to GLOBAL displacement DELTA are called primary P-DELTA moments and can be estimated by P-DELTA analysis.

While, Moments due to LOCAL displacement/buckling are called secondary P-DELTA moments and can not be estimated by P-DELTA analysis because meshed columns are generally not used n analysis. There are some approximate equations to estimate them IS:456-2000 (cl. 39.7.1).

I would like to know from SEFI members :

Which load combination shall be used while performing P-DELTA analysis?

Regards

Hemal

--- On Mon, 5/7/10, u.mukesh <forum@sefindia.org> wrote:
[quote]
From: u.mukesh <forum@sefindia.org>
Subject: [SEFI] Re: Regarding P-D analysis.
To: general@sefindia.org
Date: Monday, 5 July, 2010, 9:41 AM

Hello
I disagree with Mr. Vikramjeet.

The P-delta analysis accounts for the secondary moments due to
vertical loads on deformed structure; because of presence of horizontal loads.

For example; consider a cantilever column subjected to a vertical (P) and horizontal (H) load
at the free end. If the deflection at free end due to H is delta; so the vertical load P is also
shifted by "delta" amount. So this "PX Delta" gives the secondary moment due to vertical load.

If there is no horizontal load this moment will be zero or If we do normal analysis this moment will be zero.
So P-delta analysis does not give any moment because of "Buckling". So P-delta analysis is
useful when you have horizontal loads on the system.

Regards
Mukesh Upadhyay


On Fri, Jul 2, 2010 at 10:00 AM, truenotesrakesh forum@sefindia.org)> wrote:
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vikram.jeet
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PostPosted: Tue Jul 06, 2010 4:59 am    Post subject: Regarding P-D analysis. Reply with quote

I thank Er Hemal and Er Mukesh Upadhyaya for corrections on my posting on P-Delta analysis.

I request all sefi memebers to kindly convey their views for better understanding of the subject
of structural engineering which is very vast like ocean.

To Err is HUMAN and to correct is DIVINE

best regards

vikramjeet

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rkumar
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Joined: 11 Apr 2010
Posts: 85

PostPosted: Tue Jul 06, 2010 6:33 am    Post subject: Regarding P-D analysis. Reply with quote

Hi Seniours,
 
The horizontal loads you are writing here is the lateral loads(seismic and wind) or any horizontal loads which comes due 3d frame action also. And do free cantilver long beam do not deflect do to its self weight and shouldnt it be considered in P-D analysis. Ofcourse we do sway analysis, but for long column sway encountered is within the limit???.
RAKESH KUMAR
TRUE NOTES
BUILDING DESIGN ENGINEER

*"Please consider the environment, take a print of this copy if u really need to". Use Gently.



On Tue, Jul 6, 2010 at 11:46 AM, vikram.jeet <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  I thank Er Hemal and Er Mukesh Upadhyaya for corrections on my posting on P-Delta analysis.

I request all sefi memebers to kindly convey their views for better understanding of the subject
of structural engineering which is very vast like ocean.

To Err is HUMAN and to correct is DIVINE

best regards

vikramjeet








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thirumalaichettiar
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PostPosted: Tue Jul 06, 2010 3:21 pm    Post subject: Re: Regarding P-D analysis. Reply with quote

truenotesrakesh wrote:
Hi Seniours,

The horizontal loads you are writing here is the lateral loads(seismic and wind) or any horizontal loads which comes due 3d frame action also. And do free cantilver long beam do not deflect do to its self weight and shouldnt it be considered in P-D analysis. Ofcourse we do sway analysis, but for long column sway encountered is within the limit???.
RAKESH KUMAR
TRUE NOTES
BUILDING DESIGN ENGINEER

*"Please consider the environment, take a print of this copy if u really need to". Use Gently.



On Tue, Jul 6, 2010 at 11:46 AM, vikram.jeet <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  I thank Er Hemal and Er Mukesh Upadhyaya for corrections on my posting on P-Delta analysis.

I request all sefi memebers to kindly convey their views for better understanding of the subject
of structural engineering which is very vast like ocean.

To Err is HUMAN and to correct is DIVINE

best regards

vikramjeet








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This is with reference to Er.Heamal's posting. He has raised the question-Can we use Load combination for P-Delta analysis?
The answer is NO. You have to use REPEAT LOAD as explained under STAAD pro posting while using the STAAD PRO software.


T.Rangarajan.


Last edited by thirumalaichettiar on Sun Jul 25, 2010 3:02 am; edited 1 time in total
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lele_raj
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PostPosted: Thu Jul 08, 2010 2:14 am    Post subject: Regarding P-D analysis. Reply with quote

My understanding is more aligned with Hemal's than Mukesh's. p-delta effect occurs when an inherent assumption in the elastic analysis that strains are small compared to geomtery of the structure, breaks down. In such situations, a one-to-one relation between the cause and effect may not hold, giving rise to a "non-linearity" of the response. There are two types of nonlinearilites, geometric and material. In case of material non-linearity, structures are (generally) in a non-elastic zone of the stress/strain curve and hence this type is quite easy to understand. In the case of the first type, the structure can be in the elastic zone, but displacements are quite large. Examples are latticed structures, cable stayed bridges etc.

I've tested quite a few high voltage transmission towers on the test bed where we subject them to 100% design loads for 1,2 or 3 minutes, under various loading conditions. In other words, some members get loaded 100% more than once during the test. One of the analyses we do prior to the test, is the p-delta analysis, to give us a realistic forecast of displacements at various points under the test loads.


Best regards,

Rajendra (Raj) Lele

  
P Please consider the environment before printing this e-mail or any attachment/s.



From: hemal <forum@sefindia.org>
To: general@sefindia.org
Sent: Tue, 6 July, 2010 1:27:16 PM
Subject: [SEFI] Re: Regarding P-D analysis.

Hello,

I agree with Mr. Mukesh Upadhyay.

Moments due to GLOBAL displacement DELTA are called primary P-DELTA moments and can be estimated by P-DELTA analysis.

While, Moments due to LOCAL displacement/buckling are called secondary P-DELTA moments and can not be estimated by P-DELTA analysis because meshed columns are generally not used n analysis. There are some approximate equations to estimate them IS:456-2000 (cl. 39.7.1).

I would like to know from SEFI members :

Which load combination shall be used while performing P-DELTA analysis?

Regards

Hemal

--- On Mon, 5/7/10, u.mukesh wrote:
Quote:

From: u.mukesh
Subject: [SEFI] Re: Regarding P-D analysis.
To: general@sefindia.org (general@sefindia.org)
Date: Monday, 5 July, 2010, 9:41 AM

Hello
I disagree with Mr. Vikramjeet.

The P-delta analysis accounts for the secondary moments due to
vertical loads on deformed structure; because of presence of horizontal loads.

For example; consider a cantilever column subjected to a vertical (P) and horizontal (H) load
at the free end. If the deflection at free end due to H is delta; so the vertical load P is also
shifted by "delta" amount. So this "PX Delta" gives the secondary moment due to vertical load.

If there is no horizontal load this moment will be zero or If we do normal analysis this moment will be zero.
So P-delta analysis does not give any moment because of "Buckling". So P-delta analysis is
useful when you have horizontal loads on the system.

Regards
Mukesh Upadhyay


On Fri, Jul 2, 2010 at 10:00 AM, truenotesrakesh forum@sefindia.org (forum@sefindia.org))> wrote:
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