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Difference between Buckling and P-Delta analysis.
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hgnaikar
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PostPosted: Wed Oct 31, 2012 4:06 am    Post subject: <edited> Reply with quote

Dear All,


Buckling is effect of axial load on vertical elements like column, shear walls & walls and is dependent on axial load, cross sectional dimensions and length of the element. This is an effect on an individual compression member. The individual member may fail due to compression & flexure.


Whereas P delta effect is a result of axial load and drift of the building due to lateral loads such as Wind & Earth quake. This is an effect on the structure as a whole. The structure will be subjected to additional moments and elements will have tendency to fail by axial compression and flexure. The structure will have tendency to overturning.


Best Regards
hgn




On Tue, Oct 30, 2012 at 3:44 PM, zubairmeer1 <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
     
[edited]
     Dear rangarajan sir

i was also searching for this answer from quite a few days...and rightly said bu you a specific answer is required....lets wait and ses NS sirs reply..usually he has to the point answers....and the replies above were also excellent.. i shud accept it was a good piece of learning for me... and above all we require these types of discussions..in the forum....

what i see is P-(small delta) effect also captures this buckling effect so why buckling analysis?

little bit off the topic but.. recently i was going thru past year discussions (2003-2007)...the discussion were of totally different level....and i learnt a lot from those posts...

i request administrator to just give those members a reminder so as to take active part in the discussions and help people like me...

regards

meer
     



     


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vikram.jeet
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PostPosted: Wed Oct 31, 2012 4:55 am    Post subject: Difference between Buckling and P-Delta analysis. Reply with quote

Dear Rangarajan sir is not satisfied so far , and rightly so since both the effects
have a thin lining segregating them . Dr NS sir who always provide his expert opinion
is currently in India, may not be logging sefi regularly.Let us await his version - - -

In nut shell it seems that - -

P-Delta Effect - - - P *Delta (of Joint displacement due to sway)

Buckling - - - P *Delta (of member deflection along its length)


P - - Axial load

best regds

vikramjeet
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vikram.jeet
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PostPosted: Wed Oct 31, 2012 5:12 am    Post subject: Difference between Buckling and P-Delta analysis. Reply with quote

Minor correction in previous mail - - inconvenience regretted

Dear Rangarajan sir is not satisfied so far , and rightly so since both the effects
have a thin lining segregating them . Dr NS sir who always provide his expert opinion
is currently in India, may not be logging sefi regularly.Let us await his version - - -

In nut shell it seems that - -

P-Delta Effect - - - P *Delta (of Joint displacement due to sway)

Buckling - - - P *Delta (of member lateral deflection in its length)


P - - Axial load

best regds

vikramjeet
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thirumalaichettiar
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PostPosted: Wed Oct 31, 2012 5:48 am    Post subject: Reply with quote

Dear Er.Vikram jeet sir,

Why I am not satisfied? Because as a practical designer and on site construction  aspect need to know clearly when the buckling will take place  , on what element and how to solve and where to use the buckling analysis and the same for P Delta aspect and their effect on different materials . I do not want  a story like description but narrow short useful versions that can be easily followed by even the freshers.

Hope I made it clear now.

Since we have to wait for Dr.N.S that means out of 14,600 sefians no on can make it up?

T.RangaRajan.
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zubairmeer1
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PostPosted: Wed Oct 31, 2012 6:04 am    Post subject: Reply with quote

dear vikramjeet sir

my doubt is p-(small delta) also takes P*(lateral deflection of column)...what is the diff. between P-(small delta) and buckling analysis..

UBC-97 code has criteria for when to use p-delta anlysis in clause 1630.1.3

how to judge when to go for buckling analysis then

dear rangarajan sir.. i think many of the senior sefians are busy with office work so not able to participate..bcs we have very intelligent engineers in the forum....



regards

meer
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sarfaraj.husain
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PostPosted: Wed Oct 31, 2012 6:18 am    Post subject: Difference between Buckling and P-Delta analysis. Reply with quote

agree with hgn......
buckling is individual capacity of any comp member while........ P delta effect is shared by whole frame along a particular bay....


sarfraj



From: "hgnaikar" <forum@sefindia.org>
To: general@sefindia.org,  
Date: 10/31/12 11:08 AM
Subject: [SEFI] Re: Difference between Buckling and P-Delta analysis.



Dear All,


Buckling is effect of axial load on vertical elements like column, shear walls & walls and is dependent on axial load, cross sectional dimensions and length of the element. This is an effect on an individual compression member. The individual member may fail due to compression & flexure.


Whereas P delta effect is a result of axial load and drift of the building due to lateral loads such as Wind & Earth quake. This is an effect on the structure as a whole. The structure will be subjected to additional moments and elements will have tendency to fail by axial compression and flexure. The structure will have tendency to overturning.


Best Regards
hgn




On Tue, Oct 30, 2012 at 3:44 PM, zubairmeer1 forum@sefindia.org)> wrote:   --auto removed--

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Dr. N. Subramanian
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PostPosted: Wed Oct 31, 2012 6:28 am    Post subject: Re: Difference between Buckling and P-Delta analysis. Reply with quote

Dear Er Rangarajan,

As you are aware, buckling analysis is different from P-Delta analysis. P-Delta analysis is used for the non-linear analysis, especially when you suspect that the deflection will be non-linear due to flexible nature of the structure, lateral load, etc.

Buckling analysis may be used to find the buckling load when you have slender members, which may buckle without attaining plastic strength. It is basically in the linear range, though non-linear buckling analysis has also been attempted.


Regards,
NS
thirumalaichettiar wrote:
What is the difference between Buckling and P-Delta analysis?
When to use?

T.RangaRajan.
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ananthansemban
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PostPosted: Wed Oct 31, 2012 12:01 pm    Post subject: Difference between Buckling and P-Delta analysis. Reply with quote

Hi all,

I would like to add on to what has been discussed on this topic. There are not two but three cases that we should see. This opinion is applicable for line elements alone-


a. P-Δ (P-Capital Delta, will be refered to as P-CD here after) is effect associated with the global behaviour under a lateral and longitudinal load on a compression member. Usually the lateral load comes from seismic or wind shears.
 
b. P-δ (P-Small delta, will be refered to as P-sd) is the effect associated with the member under going secondary deformations under longitudinal compressive load because the line of action of force may not be straight. Imperfections in members causes such bends in force paths that local moments are created which magnify under continuous deformation. 


Both P-CD and P-sd are nonlinear analysis procedures with nonlinearity in material property and geometry of the member. Both material and geometric properties changes along with load/displacement increment. 
To design members P-CD analysis are used. But to determine the member capacity, P- sd can be adopted instead of conducting buckling analysis. However proper research must be conducted on the stress-strain relation of material and type of imperfection and how best it could be modeled. If you take a look at the load vs deformation plot, it is linear until the member plastifies across the cross section, gradually reaches a peak and continues to dip down. The load value corresponding to the peak would be capacity of column under axial load.  It is advised to use a displacement increment to capture capacity of member. 


c. Buckling analysis- is a geometrically non-linear elastic analysis procedure. When we look at the load vs deformation plot of an axially loaded compressive member (free of imperfection, material changes etc. or simply Euler column), the plot rises linearly from zero and suddenly becomes a straight line parallel to the axis representing deformation at the 'bifurcation point'. Value of load at bifurcation point is the buckling load of that member. For sufficiently long members, the capacities obtained from P-sd and Buckling analysis must be comparable. So it is always useful to do both P-sd and buckling analysis just to be sure of your values.


Thanks,
Ananthan







On Wed, Oct 31, 2012 at 11:07 AM, vikram.jeet <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Rangarajan sir is not satisfied so far , and rightly so since both the effects
have a thin lining segregating them . Dr NS sir who always provide his expert opinion
is currently in India, may not be logging sefi regularly.Let us await his version - - -

In nut shell it seems that - -

P-Delta Effect - - - P *Delta (of Joint displacement due to sway)

Buckling - - - P *Delta (of member deflection along its length)


P - - Axial load

best regds

vikramjeet
-- ­­
     



     



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thirumalaichettiar
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PostPosted: Wed Oct 31, 2012 2:10 pm    Post subject: Reply with quote

I got a PDF file on HAND CALCULATIONS FOR LOCAL AND DISTORTIONAL BUCKLING OF A LIPPED CHANNEL COLUMN. This may help to understand for designing steel columns.

It is in FPS units but can be studied as a guidance.

I am posting this since it may throw some information on BUCKLING.

T.RangaRajan.



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thirumalaichettiar
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PostPosted: Wed Oct 31, 2012 4:23 pm    Post subject: Reply with quote

In continuation of my previous post I am attaching a PDF file showing the CRITICAL LOAD FORMULE for various end conditions. The critical loads due to buckling depends on the length of the member, end conditions , the value of E Young's modulus and stiffness of the member.

T.RangaRajan.



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