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anand.shah1 SEFI Member
Joined: 26 Jan 2003 Posts: 13
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Posted: Fri Dec 24, 2004 11:33 am Post subject: permissible limit of drift |
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I am designing two storey college building in zone 5. caculated Storey drift is 17 mm . and allowable is 0.004 * H as per code is 14 mm. All columns and beams I have designed as per requirements of code 1893,13920 and 456. Reinf. % dosnt exceed 2.6% in any column. Even beams are not so heavily reinforced. So, do I need to change sizes of members to control storey drift ( though it is not design requirement)? or Any other suggestion? I have considered rigid diaphram action bcs slab is rigid.
Regards Anand
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ishacon1 ...
Joined: 26 Jan 2003 Posts: 52
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Posted: Fri Dec 24, 2004 3:04 pm Post subject: permissible limit of drift |
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Dear Anand,
You will need to increase the column sizes to cut down on the drift. Also ensure that there is no torsion irregularity. You may want to increase IY & IZ of beams to account for diaphragm action of slab. This will automatically reduce your drift somewhat.
V.P.Agarwal
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saistructure SEFI Regulars
Joined: 26 Jan 2003 Posts: 28
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Posted: Sat Dec 25, 2004 8:11 am Post subject: permissible limit of drift |
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Dear Anand,
Kindly inform which software you have used and how diaphragm action has been ensured while modelling. For which loadcase you got 17 mm drift?
Hiren Desai
Anand.shah@babtieindia.com wrote: I am designing two storey college building in zone 5. caculated Storey drift is 17 mm . and allowable is 0.004 * H as per code is 14 mm. All columns and beams I have designed as per requirements of code 1893,13920 and 456. Reinf. % dosnt exceed 2.6% in any column. Even beams are not so heavily reinforced. So, do I need to change sizes of members to control storey drift ( though it is not design requirement)? or Any other suggestion? I have considered rigid diaphram action bcs slab is rigid.
Regards Anand
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Rudra Nevatia ...
Joined: 26 Jan 2003 Posts: 215
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Posted: Mon Dec 27, 2004 3:16 pm Post subject: permissible limit of drift |
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I am confused.
I was taught that arbitrarily increasing out-of-plane stiffness of beams to account for diaphragm action results in large off-diagonal elements in the global stiffness matrix and the resulting system of equations can be ill-coditioned giving wrong results from an otherwise well behaved software.
But then this was thirty five years ago.
Rudra Nevatia
--- ishacon@vsnl.net wrote:
Quote: | You may want to increase IY & IZ of beams to account for diaphragm action of slab.
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