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Beam Torsion in ETABS
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ishacon
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PostPosted: Fri Mar 08, 2013 9:58 am    Post subject: Beam Torsion in ETABS Reply with quote

Our experience with ETABS on design of beams has not been satisfactory
and we tend to take these results with a pinch of salt.

Beam behaviour is best judged from STAAD or GTS STRUDL.

VP Agarwal
ISHA CONSULTANTS (P) LTD
NEW DELHI 110074

PH : 011-2630 1158 ; 08010071749
08010071749 ; 093 1345 2180
Quote:
-- Original Message --
From: Kumar_Abhishek_Singh (forum@sefindia.org)
To: general@sefindia.org (general@sefindia.org)
Sent: Wednesday, March 06, 2013 12:36 PM
Subject: [SEFI] Beam Torsion in ETABS


Dear All,

Can anyone please let me know how to release torsion in beams modelled in etabs?
The beams that generally passed in STAAD even without torsion release are failing in etabs in combined shear and torsion.

Generally do you guys also face problems in beam design in ETABS? I think it unnecessarily calls for extra beam width.

Thanks
Abhishek






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surendra
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PostPosted: Fri Mar 08, 2013 2:06 pm    Post subject: Beam Torsion in ETABS Reply with quote

Dear Abhishek,

As said below, we should be very care full in torsion. We should see whether torsion can be really released or not. If it can be released detailing shall be done accordingly.  

However in ETABS you can select concern beams go to property modifier give torsional stiffness 0.01.

In etabs you use this : Assign - Frame/line – Property modifier – Torsional constant : Give as 0.01.  

Regards,

Surendra babu J

From: SANGEETA WIJ [mailto:forum@sefindia.org]
Sent: Friday, March 08, 2013 5:53 PM
To: general@sefindia.org
Subject: [SEFI] Re: Beam Torsion in ETABS



Dear Abhishek
When in doubt, always do a manual check, for couple of important beams, and please do not forget that releasing torsion must also be followed with correct detailing of secondary beam r/f at junction with main beam.If this is not diligently followed, the release will stay only in the model, and will not happen in the actual structure.
Regards
Sangeeta Wij

From: Kumar_Abhishek_Singh [mailto:forum@sefindia.org (forum@sefindia.org)]
Sent: 06 March 2013 12:36
To: general@sefindia.org (general@sefindia.org)
Subject: [SEFI] Beam Torsion in ETABS



Dear All,

Can anyone please let me know how to release torsion in beams modelled in etabs?
The beams that generally passed in STAAD even without torsion release are failing in etabs in combined shear and torsion.

Generally do you guys also face problems in beam design in ETABS? I think it unnecessarily calls for extra beam width.

Thanks
Abhishek  





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prof.arc
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PostPosted: Fri Mar 08, 2013 11:22 pm    Post subject: Beam Torsion in ETABS Reply with quote

I find it interesting that questions are posed on
" releasing some physical actions" as an analytical tool
I wonder whether actual construction would reflect such release

the two release actions most discussed in this forum are
assuming a theoretical hinge in base of lowermost column
and effect of torsion in main beam due to secondary beam
connected to it

if the construction does not reflect enabling such release
i feel the analytical tool of release should not be used

ARC

On 3/6/13, Kumar_Abhishek_Singh <forum@sefindia.org> wrote:
Quote:
Dear All,

Can anyone please let me know how to release torsion in beams modelled in
etabs?
The beams that generally passed in STAAD even without torsion release are
failing in etabs in combined shear and torsion.

Generally do you guys also face problems in beam design in ETABS? I think it
unnecessarily calls for extra beam width.

Thanks
Abhishek


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prof.arc
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PostPosted: Fri Mar 08, 2013 11:22 pm    Post subject: Beam Torsion in ETABS Reply with quote

On 3/9/13, Prof ARC <prof.arc@gmail.com> wrote:
Quote:
I find it interesting that questions are posed on
" releasing some physical actions" as an analytical tool
I wonder whether actual construction would reflect such release

the two release actions most discussed in this forum are
assuming a theoretical hinge in base of lowermost column
and effect of torsion in main beam due to secondary beam
connected to it

if the construction does not reflect enabling such release
i feel the analytical tool of release should not be used

ARC

On 3/6/13, Kumar_Abhishek_Singh <forum@sefindia.org> wrote:
Quote:
Dear All,

Can anyone please let me know how to release torsion in beams modelled in
etabs?
The beams that generally passed in STAAD even without torsion release are
failing in etabs in combined shear and torsion.

Generally do you guys also face problems in beam design in ETABS? I think
it
unnecessarily calls for extra beam width.

Thanks
Abhishek



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Rajiv
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PostPosted: Sat Mar 09, 2013 4:57 am    Post subject: Beam Torsion issue in ETABS Reply with quote

Dear Vijay and Abhishek:

It is not advisable to have a very low value of property modifier. This may create numerical issues. If you wish to reduce torsion in beams then you can have a value of torsional stiffness modifier as 0.1. This will reduce torsion.  However please note that you can't apply this for all cases.

If your model in ETABS and other programs is identical then design produced will be similar.

regards

Rajiv
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Rajiv
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PostPosted: Sat Mar 09, 2013 5:01 am    Post subject: ETABS Beam Design issues Reply with quote

Dear Mr. Agarwal:

Could you please tell us the basis of your statement that ETABS design is not satisfactory ? We may perhaps learn something from this.

regards

Rajiv
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lkjain.ngp
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Posts: 36

PostPosted: Tue Mar 12, 2013 1:03 pm    Post subject: Beam Torsion in ETABS Reply with quote

Dear sirs,

Release of end moment of a secondary beam supported by primary beam,
is permitted on meeting some detailing requirements.
It is assumed that release is permitted due to an action of
development of plastic hing mechanism.
Before release some force actions can be envisaged i.e. some end
moment in secondary beam and torsion in primary beam. Due to the
effect of cracking, the stiffness (which produces these actions i.e.
BM & torsion) will reduce, and force action produced will be much
smaller (torsion). This smaller force actions (say torsion) can be
assumed to be the limiting plastic action. Detailing should be such
that the primary beam takes such force actions (say torsion) in
addition. Little extra shear capacity and & closely spaced stirrups
(in relation to core width of beam) are needed.
The conditions of release was dealt in DIN 1045 versions which I saw in 70's.

L. K. JAIN

On 09/03/2013, prof.arc <forum@sefindia.org> wrote:
Quote:
I find it interesting that questions are posed on
" releasing some physical actions" as an analytical tool
I wonder whether actual construction would reflect such release

the two release actions most discussed in this forum are
assuming a theoretical hinge in base of lowermost column
and effect of torsion in main beam due to secondary beam
connected to it

if the construction does not reflect enabling such release
i feel the analytical tool of release should not be used

ARC

On 3/6/13, Kumar_Abhishek_Singh <forum@sefindia.org> wrote:

Quote:
Dear All,

Can anyone please let me know how to release torsion in beams modelled in
etabs?
The beams that generally passed in STAAD even without torsion release are
failing in etabs in combined shear and torsion.

Generally do you guys also face problems in beam design in ETABS? I think
it
unnecessarily calls for extra beam width.

Thanks
Abhishek









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cckeshav
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PostPosted: Fri Mar 15, 2013 6:43 am    Post subject: Beam Torsion in ETABS Reply with quote

Dear SEFIans:

Most codes of practice allow releasing or ignoring torsion moments in design (only compatibility torsion) if the torsional stiffness is not taken into account in analysis. Please refer IS 456-2000 cl. 41.1. This clearly indicates that we can assume the torsional stiffness to be small in analysis so as to avoid compatibility torsion. Please note that whatever be the torsional stiffness, equilibrium torsion still gets generated (albeit with large rotations). As such even a careless specification of low trosional stiffness for all members does not result in undue problems in design (note that we are not analysing for large deformations here).

Further, countless number of structures have been designed using the two dimensional plane frame assumptions and they are still performing adequately all over the world.

Also, it should be noted that in most building structures, there are floor slabs which automatically take up any torsional forces and prevent their transfer to beams. As such careful detailing of beams to reflect the assumption of no torsion may not be necessary.

Due to all these reasons, it is adequate if a small torsional stiffness is specified during analysis of structures.

With Regards
C.Channakeshava


Subject: [SEFI] Re: Beam Torsion in ETABS
From: forum@sefindia.org
Date: Thu, 14 Mar 2013 01:10:51 +0530
To: general@sefindia.org

           Dear sirs,

Release of end moment of a secondary beam supported by primary beam,
is permitted on meeting some detailing requirements.
It is assumed that release is permitted due to an action of
development of plastic hing mechanism.
Before release some force actions can be envisaged i.e. some end
moment in secondary beam and torsion in primary beam. Due to the
effect of cracking, the stiffness (which produces these actions i.e.
BM & torsion) will reduce, and force action produced will be much
smaller (torsion). This smaller force actions (say torsion) can be
assumed to be the limiting plastic action. Detailing should be such
that the primary beam takes such force actions (say torsion) in
addition. Little extra shear capacity and & closely spaced stirrups
(in relation to core width of beam) are needed.
The conditions of release was dealt in DIN 1045 versions which I saw in 70's.

L. K. JAIN

On 09/03/2013, prof.arc wrote:
      --auto removed--

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ASHFAQUE NISAR ANSARI
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PostPosted: Sat Mar 16, 2013 8:37 am    Post subject: Beam Torsion in ETABS Reply with quote

Dear Abhishek
while defining frame section,click on set modifier.you will get
analysis property modification factors.then make torsional constant as
0.
Ashfaque Ansari

On 3/6/13, Kumar_Abhishek_Singh <forum@sefindia.org> wrote:
Quote:
Dear All,

Can anyone please let me know how to release torsion in beams modelled in
etabs?
The beams that generally passed in STAAD even without torsion release are
failing in etabs in combined shear and torsion.

Generally do you guys also face problems in beam design in ETABS? I think it
unnecessarily calls for extra beam width.

Thanks
Abhishek









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Manoharbs_eq
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PostPosted: Sat Mar 16, 2013 9:13 am    Post subject: Reply with quote

Dear sir,

"As such even a careless specification of low trosional stiffness for all members does not result in undue problems in design (note that we are not analysing for large deformations here)."


IT is not advisable to release torsion in all the elements of the structure analysed. I agree that in past many structures analysed by 2d frame by moment distribution and kani's are still in service. However we Humans evolve , before structures were designed only for gravity,then we adopted lateral loads from various forces. So it is evolution not a constant.




It is better not to release generally,however in exception cases for few beams it can be adopted.


Rgds
Manohar





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