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STAAD TORSION RELEASE

 
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hemal
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PostPosted: Tue May 17, 2011 12:10 pm    Post subject: STAAD TORSION RELEASE Reply with quote

Dear SEFI members,

I have seen many people releasing moment Mx (torsion for beam) at only start node of all main beams (beams connecting columns) in a 3D space structure with moment resisting Rc frames to avoid torsion in main beams. Structure is also subjected to wind and seismic forces. Is it proper way of avoiding torsion in beam?

Regards
Hemal

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suresh_sharma
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Joined: 23 Mar 2011
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PostPosted: Tue May 17, 2011 12:53 pm    Post subject: Reply with quote

Dear Hemal,

What I feel that you mean Mz and not Mx. Mx of the secondary beam will not cause torsion in the main beam. Please confirm.
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sakumar79
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PostPosted: Tue May 17, 2011 2:07 pm    Post subject: Reply with quote

Dear Sirs,
    Mr. Hemal is right - Mx is released in start node of all members to release torsion. This is common practice by many...

   In my humble opinion, a regular system can be stable without torsion being induced. In the case of horizontal loads, one needs to ensure center of rigidity and center of mass must coincide. Then there is no overall torsion induced...

There are two types of torsional forces that can be present in a structure - Equilibrium Torsion and Compatibility torsion.

For a statically determinate structure, there is only one path along which a torsional moment can be transmitted to the supports. This type of torsional moment, which is referred to as equilibrium torsion, cannot be reduced by redistribution of internal forces or by a rotation of member.

The torsional moment in a particular part of a statically indeterminate structure may be substantially reduced if that part of the structure cracks under torsion and/or rotates. The result will be a redistribution of forces in the structure. This type of torsion is referred to as compatibility torsion, in the sense that part of structure in question twists in order to keep the deformations of the structure compatible.


Essentially, by releasing MX in start member in all nodes, you are avoiding compatibillity torsion. That is okay... This should be avoided only where you expect torsion like in curved beams or cantilever beam resting on cross beam...

STAAD allows users to release moments in both ends. Some software like ETABS only allow the release in either end. If you release Mx in both ends, you risk running into problems of equilibrium torsion being affected, hence it is better to avoid it. When STAAd encounters problem of  equilibrium torsion being affected , it will give stiffness warning and if you look at deflections, there will be some huge displacements (linear and/or angular)...

Arun
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hemal
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PostPosted: Wed May 18, 2011 1:28 am    Post subject: STAAD TORSION RELEASE Reply with quote

Dear Mr. Sharma,

There is no secondary beam in structure. All beams are main beam connecting columns and released for Mx at start node only.

Regards

--- On Tue, 17/5/11, suresh_sharma <forum@sefindia.org> wrote:
Quote:

From: suresh_sharma <forum@sefindia.org>
Subject: [SEFI] Re: STAAD TORSION RELEASE
To: general@sefindia.org
Date: Tuesday, 17 May, 2011, 7:53 AM

           Dear Hemal,

What I feel that you mean Mz and not Mx. Mx of the secondary beam will not cause torsion in the main beam. Please confirm.
     



     


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suresh_sharma
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PostPosted: Thu May 19, 2011 3:41 am    Post subject: Reply with quote

Dear Arun,
what I feel that reference to "Start" of beam in your posting may be understood as one end of the beam irrespective of whether it is start or end. I confront you with the follwing situations to post your valuable comments.

i) Central column with beams on all four sides of column. Whether the end of all the four beams connected to the above column can be released for Mx at the junction of beams and column.
ii) Side column with beams on three sides of the column. Can we think of releasing the end of all the three beams joined to the column?
iii) Side columns with two  collinear beams. Can we release Mx for both the beams joined to the column?
iv) Corner column with two beams at right angle. Whether release as aforesaid can be implemented?

Suresh
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sakumar79
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PostPosted: Thu May 19, 2011 4:49 am    Post subject: Reply with quote

suresh_sharma wrote:
Dear Arun,
what I feel that reference to "Start" of beam in your posting may be understood as one end of the beam irrespective of whether it is start or end. I confront you with the follwing situations to post your valuable comments.

i) Central column with beams on all four sides of column. Whether the end of all the four beams connected to the above column can be released for Mx at the junction of beams and column.
ii) Side column with beams on three sides of the column. Can we think of releasing the end of all the three beams joined to the column?
iii) Side columns with two  collinear beams. Can we release Mx for both the beams joined to the column?
iv) Corner column with two beams at right angle. Whether release as aforesaid can be implemented?


Suresh


Dear Sir,
  When I say Start node, it is only for convenience, it can be all end nodes also... In all four cases you have mentioned, torsion can be released. Whether you are releasing torsion in the near end of a joint or a far end of a joint does not matter for compatibility torsion.  Unless the member itself is subjected to a torsion (applied UDT or point torsion), if one end cannot take torsion, no torsion will be present in the other end. Please correct me if I am wrong.

Arun
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suresh_sharma
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PostPosted: Thu May 19, 2011 7:00 am    Post subject: Reply with quote

Dear Arun,
All that you have stated appears to be OK except the last one. How is it that by releasing Mx at one end of the beam, you can rest assured that there will be no torsion at the other end. Simple example could be that of holding stick in one hand and trying to rotate the stick at the other end which is free. Would not the torsion be felt at the hand which is holding the stick. The only possibility that I am envisaging that in absence of UDL moment or concentrated moment load across the member or you can say beam, major torsion may not develop. One has to be very very particular that there is no balcony or projected slab resting on such beams which you have already elaborated in your posting.

Please clarify and help me in getting over from the confused state.
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sakumar79
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PostPosted: Thu May 19, 2011 8:53 am    Post subject: Reply with quote

Dear Mr. Sharma,
   You are talking about Equilibrium Torsion whereas I have clearly said that I am talking about Compatibility torsion. Please refer to my earlier post on differences between the two...

Arun
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hemal
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PostPosted: Thu May 19, 2011 10:07 am    Post subject: STAAD TORSION RELEASE Reply with quote

Dear Mr. Arun,

Releasing main beams at both end for Mx (torsion) may sometimes cause instability if main beam is receiving torsion from secondary beams (if not released) or from cantilever beam.

Even if the beam is released for Mx at one or both end, u will still get some (many times considerable) torsion moment in the beam.

Many times if structure is released for particular DOF, and if some forces acting on the structure are related to that DOF, you will either get instability message or some forces in the member corresponding to that DOF, depending upon the internal programming of software u r using.


Regards
Hemal
Hemal

--- On Wed, 18/5/11, sakumar79 <forum@sefindia.org> wrote:
Quote:

From: sakumar79 <forum@sefindia.org>
Subject: [SEFI] Re: STAAD TORSION RELEASE
To: general@sefindia.org
Date: Wednesday, 18 May, 2011, 11:49 PM

                  suresh_sharma wrote:                Dear Arun,
what I feel that reference to "Start" of beam in your posting may be understood as one end of the beam irrespective of whether it is start or end. I confront you with the follwing situations to post your valuable comments.

i) Central column with beams on all four sides of column. Whether the end of all the four beams connected to the above column can be released for Mx at the junction of beams and column.
ii) Side column with beams on three sides of the column. Can we think of releasing the end of all the three beams joined to the column?
iii) Side columns with two collinear beams. Can we release Mx for both the beams joined to the column?
iv) Corner column with two beams at right angle. Whether release as aforesaid can be implemented?


Suresh     

Dear Sir,
When I say Start node, it is only for convenience, it can be all end nodes also... In all four cases you have mentioned, torsion can be released. Whether you are releasing torsion in the near end of a joint or a far end of a joint does not matter for compatibility torsion. Unless the member itself is subjected to a torsion (applied UDT or point torsion), if one end cannot take torsion, no torsion will be present in the other end. Please correct me if I am wrong.

Arun
     



     


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suresh_sharma
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PostPosted: Thu May 19, 2011 1:04 pm    Post subject: Reply with quote

To Arun,
Thank you for clarifying my doubts
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