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Doubt in Seismic Design

 
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iyer_mahadevan at redi...
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PostPosted: Sat Oct 30, 2004 8:21 am    Post subject: Doubt in Seismic Design Reply with quote

Dear sefians,

In a building if a slab alongwith plinth beams are provided at the plinth level (for parking etc.)should its seismic weight be lumped to the frame as is done for higher floor levels?

Intuitively I feel that this should not be done, as the said slab as well as beams transfer the load directly to the soil.

The IS code (IS 1893-2002) does not address this issue.

I hope you will be kind enough to clarify.

MAHADEVAN IYER
M.Tech (Structural Engg.)(3rd Sem.)
V.N.I.T. Nagpur.

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mangeshb
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Joined: 26 Jan 2003
Posts: 9

PostPosted: Sat Oct 30, 2004 12:02 pm    Post subject: Doubt in Seismic Design Reply with quote

Dear friend,
as per your mail, i think that is on the ground floor And hence
whatever is on the ground that won't come into seismic analysis due to
support on the ground.
I think well known professor DR. JAISWAL may guide you better than anybody
else.,isn't it.

regards
Mangesh Bawankar

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for_prof_arc at hotmai...
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PostPosted: Mon Nov 01, 2004 1:56 am    Post subject: Doubt in Seismic Design Reply with quote

The framed structure is to be modelled by considering the columns fixed [or
supported by equivalent soil springs] at the top of the footing. Naturally,
the mass of the plinth beam would also be considered in that model. The top
portion of the soil upto the bottom of the footing is not modelled.

If you have a block foundation, like in Machine foundations, the embedded
soil can be modelled as equivalent soil springs.

ARC
----- Original Message -----
Message From  <iyer_mahadevan@rediffmail.com>
To: <for_prof_arc@hotmail.com>
Sent: Saturday, October 30, 2004 1:51 PM
Subject: Doubt in Seismic Design


Quote:
Dear sefians,

In a building if a slab alongwith plinth beams are provided at the plinth
level (for parking etc.)should its seismic weight be lumped to the frame as
is done for higher floor levels?
Quote:

Intuitively I feel that this should not be done, as the said slab as well
as beams transfer the load directly to the soil.
Quote:

The IS code (IS 1893-2002) does not address this issue.

I hope you will be kind enough to clarify.

MAHADEVAN IYER
M.Tech (Structural Engg.)(3rd Sem.)
V.N.I.T. Nagpur.


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acpl_sefi
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Joined: 26 Jan 2003
Posts: 63

PostPosted: Mon Nov 01, 2004 8:00 pm    Post subject: Doubt in Seismic Design Reply with quote

General practise is the slab at grade level is ignored--though the mass of the ground floor does participate but to not that extent as compared to if it was unrestrained from the srrounding soil. Therefore it is justified to ignire the mass for seismic analysis. Otherwise every single storey building would need to be designed as a two storey building. Of course it is modelled with the plinth beam and even raft/ grade beams if provided, though without the mass at the ground level--but it is unfair to over penalise the roof beams because of limited participation of the ground floor mass

Vipul Ahuja  


On Mon, 01 Nov 2004 for_prof_arc@hotmail.com wrote :
The framed structure is to be modelled by considering the columns fixed [or
supported by equivalent soil springs] at the top of the footing. Naturally,
the mass of the plinth beam would also be considered in that model. The top
portion of the soil upto the bottom of the footing is not modelled.

If you have a block foundation, like in Machine foundations, the embedded
soil can be modelled as equivalent soil springs.

ARC
----- Original Message -----
Message From  &lt;iyer_mahadevan@rediffmail.com
To: &lt;for_prof_arc@hotmail.com
Sent: Saturday, October 30, 2004 1:51 PM
Subject: Doubt in Seismic Design


Dear sefians,

In a building if a slab alongwith plinth beams are provided at the plinth
level (for parking etc.)should its seismic weight be lumped to the frame as
is done for higher floor levels?

Intuitively I feel that this should not be done, as the said slab as well
as beams transfer the load directly to the soil.

The IS code (IS 1893-2002) does not address this issue.

I hope you will be kind enough to clarify.

MAHADEVAN IYER
M.Tech (Structural Engg.)(3rd Sem.)
V.N.I.T. Nagpur.




Structural Engineers Forum of India

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