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permissible limit of drift

 
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anand.shah1
SEFI Member
SEFI Member


Joined: 26 Jan 2003
Posts: 13

PostPosted: Fri Dec 24, 2004 11:33 am    Post subject: permissible limit of drift Reply with quote

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
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Joined: 26 Jan 2003
Posts: 52

PostPosted: Fri Dec 24, 2004 3:04 pm    Post subject: permissible limit of drift Reply with quote

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
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Joined: 26 Jan 2003
Posts: 28

PostPosted: Sat Dec 25, 2004 8:11 am    Post subject: permissible limit of drift Reply with quote

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
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...


Joined: 26 Jan 2003
Posts: 215

PostPosted: Mon Dec 27, 2004 3:16 pm    Post subject: permissible limit of drift Reply with quote

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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