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Lateral bracing of columns for G+13 Structure
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P.K.Mallick
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PostPosted: Wed Jan 21, 2009 4:49 pm    Post subject: Re: Lateral bracing of columns for G+13 Structure Reply with quote

Depending on the thickness of slab and reinforcement provided in slab, the slab will provide certain amount of resistance to prevent the sway of column. Let us assume three scenarios
1)     The strip of slab connecting column to column contains reinforcement only for cylindrical bending of slab. The resistance to sway is negligible.
2)     The strip of slab contains reinforcement as in the case of a column strip of a flat slab. This provides certain resistance to sway. The stiffness can be calculated based on transformed section where reinforcement transformed based on modular ratio and accordingly the resistance to sway.
3)     The strip contains one or several steel beams of height same as slab. Let us assume that those several steel beams are connected transversely to behave in an integrated manner. This will certainly provide a good amount stiffness to resist the lateral sway. Of course on need to take special care for connectivity of concrete column and steel beam.
The proposition at (3) shall certainly satisfy the requirement of an ordinary moment resisting frame with response reduction factor of 3 and it can be combined with ductile shear wall to enhance the response reduction factor to 4.5. The strip containing several steel beam shall also prevent out of plane bending of slab  and improve diaphragm action.
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ajeetkokil
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PostPosted: Thu Jan 22, 2009 7:29 am    Post subject: Lateral bracing of columns for G+13 Structure Reply with quote

Subramanian Sir

1) I asked this question because shear wall is a flexural element which resist incoming lateral loads through flexural behavior. So its use in tall buildings to control the deflection / drifts of the buildings under seismic or wind loads is justified. However, for shorter buildings, beam-column-rigid diphragm arrangement should work. Is it ok?
2) If the building is in the shape of sector of a circle, building height 30m (4 stories)& is located in high seismic zone, then beam column & rigid diphragm system should work. will it?

Thanks in advance

Ajit


On Wed, 21 Jan 2009 drnsmani wrote :
Quote:
Hi Ajeetkokil,

If the building is less than 4 stories and in not in severe earthquake zone, I feel that you may provide reinforced infill walls.

Best wishes
Subramanian

[Image: http://us.i1.yimg.com/us.yimg.com/i/mesg/tsmileys2/23.gif ]Dr.N.Subramanian,Ph.D.,F.ASCE, M.ACI,

Consulting Structural Engineer
Maryland, USA

See my books at: www.multi-science.co.uk/subramanian-book.htm (http://www.multi-science.co.uk/subramanian-book.htm)
www.oup.co.in/search_detail.php?id=144559 (http://www.oup.co.in/search_detail.php?id=144559)





--- On Wed, 1/21/09, ajeetkokil <forum@sefindia.org> wrote:
Quote:
From: ajeetkokil <forum@sefindia.org>
Subject: [SEFI] Re: Lateral bracing of columns for G+13 Structure
To: general@sefindia.org
Date: Wednesday, January 21, 2009, 4:58 PM

Dear Subramanian Sir,

What would be your suggestion if the building is not that tall as Mr. Rajgarhwala is saying, say it is 4 storey building with the height of 30m?

Thanks
On Wed, 21 Jan 2009 drnsmani wrote :
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Ajit Shankar Kokil





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skjain.iitk
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PostPosted: Thu Jan 22, 2009 1:22 pm    Post subject: Lateral bracing of columns for G+13 Structure Reply with quote

Dear Mr Rajgarhwala:

I will not recommend such a system regardless of the seismic zone and regardless of the number of stories. You need a proper "lateral load resisting system" which may be a set of shear walls and/or moment resisting frames in both the directions.

Basically, your architect needs to understand what type of members are needed so that the horizontal forces can be safely transferred to the foundation. If you have a difficulty explaining to him basic concepts of lateral load resisting systems, I suggest you recommend to him to go through the book/CD "Earthquake Design Concepts" by C V R Murty and Andrew Charleson. It contains more than 600 power point slides to explain various issues on seismic safety of buildings to ARCHITECTS. Indeed, this volume is written for architects, and hence, treats the subject only at the conceptual level, without going into mathematics or calculations.

With best wishes on your project.

Sudhir K Jain
IIT Kanpur

On 1/20/09, rajgarhwala <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  Sir,
I am designing a G+13 Structure in EQ Zone III. Due to architectural constraint, I can not provide bracing beams in transverse direction. Is it okay to provide only slab, and consider the columns braced in transverse direction. or otherwise should I provide a steel "I" section whose depth matches slab thickness.
thanks
Hasan Rajgarhwala







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rajgarhwala
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PostPosted: Thu Jan 22, 2009 3:39 pm    Post subject: Re: Lateral bracing of columns for G+13 Structure Reply with quote

Dear Sir,
Thanks for all your suggestions. I will keep all your valuable suggestions.
Thanks
Hasan
skjain.iitk wrote:
Dear Mr Rajgarhwala:

I will not recommend such a system regardless of the seismic zone and regardless of the number of stories. You need a proper "lateral load resisting system" which may be a set of shear walls and/or moment resisting frames in both the directions.

Basically, your architect needs to understand what type of members are needed so that the horizontal forces can be safely transferred to the foundation. If you have a difficulty explaining to him basic concepts of lateral load resisting systems, I suggest you recommend to him to go through the book/CD "Earthquake Design Concepts" by C V R Murty and Andrew Charleson. It contains more than 600 power point slides to explain various issues on seismic safety of buildings to ARCHITECTS. Indeed, this volume is written for architects, and hence, treats the subject only at the conceptual level, without going into mathematics or calculations.

With best wishes on your project.

Sudhir K Jain
IIT Kanpur

On 1/20/09, rajgarhwala <forum> wrote:
Quote:
  Sir,
I am designing a G+13 Structure in EQ Zone III. Due to architectural constraint, I can not provide bracing beams in transverse direction. Is it okay to provide only slab, and consider the columns braced in transverse direction. or otherwise should I provide a steel "I" section whose depth matches slab thickness.
thanks
Hasan Rajgarhwala







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prof.arc
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PostPosted: Fri Jan 23, 2009 12:48 am    Post subject: Lateral bracing of columns for G+13 Structure Reply with quote

Quote:
building height 30m (4 stories)& is located in high seismic zone, then beam column & rigid >diphragm system should work.

anything will work as long as they are properly modelled, analysed, designed and CONSTRUCTED as per design !!

ARC

On Thu, Jan 22, 2009 at 1:14 PM, ajeetkokil <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Subramanian Sir

1) I asked this question because shear wall is a flexural element which resist incoming lateral loads through flexural behavior. So its use in tall buildings to control the deflection / drifts of the buildings under seismic or wind loads is justified. However, for shorter buildings, beam-column-rigid diphragm arrangement should work. Is it ok?
2) If the building is in the shape of sector of a circle, building height 30m (4 stories)& is located in high seismic zone, then beam column & rigid diphragm system should work. will it?

Thanks in advance



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