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rkumar ...
Joined: 11 Apr 2010 Posts: 85

Posted: Sat Jun 26, 2010 10:15 am Post subject: Regarding PD analysis. 


Hello Seniours,
Â
I need your guidance in this topic. When do we use PDelta analysis, when it becomes necessary to do pdelta analysis and how to do pdelta analysis, what is its major applications, advantages and disadvantages. Upto what extent it is in use nowadays in INDIA.
Â
waiting for your answers
Â
with regards
Â
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 SEFI Member
Joined: 20 Jun 2010 Posts: 9

Posted: Sun Jun 27, 2010 5:30 am Post subject: 


Dear Engineer,
PDelta 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 PDELTA 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:
1Non Linear Second Order Analysis
2Elastic Second Order Analysis (which we commonly use in Etabs by provind frame modifiers)
3Moment 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 Secondorder 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 General Sponsor
Joined: 26 Jan 2003 Posts: 2212

Posted: Wed Jun 30, 2010 10:15 am Post subject: Regarding PD analysis. 


PDelta Analysis
In my opinion:
Pdelta 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 pdelta effects if structural proportions of
columns/beams in a frame are inadequate visa vis height/span respectively
Additional moments depend upon the slenderness of member .
Pdelta effect is applicable to all members .However keeping in view the magnitude
of its effect, the members are treated as Slender members or Nonslender 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 Pdelta analysis but formulae are
available to determine the additional moments due to Pdelta effect.
For Mega structures like Central tower of a Cable stayed bridge and similar,
the rigorous Pdelta analysis is required
Tall Structures subject to sway under the action of horizontal forces could also
suffer from the Pdelta 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 ...
Joined: 11 Apr 2010 Posts: 85

Posted: Fri Jul 02, 2010 4:24 am Post subject: Regarding PD analysis. 


Hello Mr Vikram Jeet,
Â
Thanking you sir. It was a helpful guidance from you.
Â
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:  PDelta Analysis
In my opinion:
Pdelta 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 pdelta effects if structural proportions of
columns/beams in a frame are inadequate visa vis height/span respectively
Additional moments depend upon the slenderness of member .
Pdelta effect is applicable to all members .However keeping in view the magnitude
of its effect, the members are treated as Slender members or Nonslender 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 Pdelta analysis but formulae are
available to determine the additional moments due to Pdelta effect.
For Mega structures like Central tower of a Cable stayed bridge and similar,
the rigorous Pdelta analysis is required
Tall Structures subject to sway under the action of horizontal forces could also
suffer from the Pdelta 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 General Sponsor
Joined: 26 Jan 2003 Posts: 98 Location: Delhi

Posted: Mon Jul 05, 2010 8:40 am Post subject: Regarding PD analysis. 


Hello
I disagree with Mr. Vikramjeet.
The Pdelta 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 Pdelta analysis does not give any moment because of "Buckling". So Pdelta 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,
Â
Thanking you sir. It was a helpful guidance from you.
Â
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:
: PDelta Analysis
In my opinion:
Pdelta 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 pdelta effects if structural proportions of
columns/beams in a frame are inadequate visa vis height/span respectively
Additional moments depend upon the slenderness of member .
Pdelta effect is applicable to all members .However keeping in view the magnitude
of its effect, the members are treated as Slender members or Nonslender 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 Pdelta analysis but formulae are
available to determine the additional moments due to Pdelta effect.
For Mega structures like Central tower of a Cable stayed bridge and similar,
the rigorous Pdelta analysis is required
Tall Structures subject to sway under the action of horizontal forces could also
suffer from the Pdelta 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 ...
Joined: 01 Apr 2008 Posts: 129

Posted: Tue Jul 06, 2010 3:16 am Post subject: Regarding PD analysis. 


Hello,
I agree with Mr. Mukesh Upadhyay.
Moments due to GLOBAL displacement DELTA are called primary PDELTA moments and can be estimated by PDELTA analysis.
While, Moments due to LOCAL displacement/buckling are called secondary PDELTA moments and can not be estimated by PDELTA analysis because meshed columns are generally not used n analysis. There are some approximate equations to estimate them IS:4562000 (cl. 39.7.1).
I would like to know from SEFI members :
Which load combination shall be used while performing PDELTA 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 PD analysis.
To: general@sefindia.org
Date: Monday, 5 July, 2010, 9:41 AM
Hello
I disagree with Mr. Vikramjeet.
The Pdelta 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 Pdelta analysis does not give any moment because of "Buckling". So Pdelta 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 General Sponsor
Joined: 26 Jan 2003 Posts: 2212

Posted: Tue Jul 06, 2010 4:59 am Post subject: Regarding PD analysis. 


I thank Er Hemal and Er Mukesh Upadhyaya for corrections on my posting on PDelta 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 ...
Joined: 11 Apr 2010 Posts: 85

Posted: Tue Jul 06, 2010 6:33 am Post subject: Regarding PD analysis. 


Hi Seniours,
Â
The horizontal loads you are writing here is the lateral loads(seismic and wind)Â or any horizontal loads which comes due 3d frame action also. AndÂ do free cantilver long beam do not deflect do to its self weight and shouldnt it be considered in PD 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 PDelta 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 Silver Sponsor
Joined: 26 Jan 2003 Posts: 3478

Posted: Tue Jul 06, 2010 3:21 pm Post subject: Re: Regarding PD analysis. 


truenotesrakesh wrote:  Hi Seniours,
Â
The horizontal loads you are writing here is the lateral loads(seismic and wind)Â or any horizontal loads which comes due 3d frame action also. AndÂ do free cantilver long beam do not deflect do to its self weight and shouldnt it be considered in PD 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 PDelta 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

Posted via Email 
This is with reference to Er.Heamal's posting. He has raised the questionCan we use Load combination for PDelta 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 ...
Joined: 26 Jan 2003 Posts: 145

Posted: Thu Jul 08, 2010 2:14 am Post subject: Regarding PD analysis. 


My understanding is more aligned with Hemal's than Mukesh's. pdelta 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 onetoone relation between the cause and effect may not hold, giving rise to a "nonlinearity" of the response. There are two types of nonlinearilites, geometric and material. In case of material nonlinearity, structures are (generally) in a nonelastic 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 pdelta 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 email 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 PD analysis.
Hello,
I agree with Mr. Mukesh Upadhyay.
Moments due to GLOBAL displacement DELTA are called primary PDELTA moments and can be estimated by PDELTA analysis.
While, Moments due to LOCAL displacement/buckling are called secondary PDELTA moments and can not be estimated by PDELTA analysis because meshed columns are generally not used n analysis. There are some approximate equations to estimate them IS:4562000 (cl. 39.7.1).
I would like to know from SEFI members :
Which load combination shall be used while performing PDELTA analysis?
Regards
Hemal
 On Mon, 5/7/10, u.mukesh wrote:
Quote: 
From: u.mukesh
Subject: [SEFI] Re: Regarding PD analysis.
To: general@sefindia.org (general@sefindia.org)
Date: Monday, 5 July, 2010, 9:41 AM
Hello
I disagree with Mr. Vikramjeet.
The Pdelta 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 Pdelta analysis does not give any moment because of "Buckling". So Pdelta 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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