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Support conditions for analyzing G+1 Building

 
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ramu_se
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Joined: 30 Oct 2017
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PostPosted: Thu Jun 09, 2022 9:23 am    Post subject: Support conditions for analyzing G+1 Building Reply with quote

Dear All,

At what consideration do we need to fix the support conditions for analyzing the building?

For example, if we analyze a G+1 or G+2 building using Etab or staad software
do we need to assign the fixed support or pinned support?

Kindly Clarify.

Thanks,
Ramu.
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vikram.jeet
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Joined: 26 Jan 2003
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PostPosted: Fri Jun 10, 2022 3:10 am    Post subject: Reply with quote

Buildings - support condition

Isolated footings resting on Rock  / Hard strata. - Fixed

Isolated footings resting on medium/ weak soils -
With foundation tie beams - Fixed
Without foundation tie beams - Pinned


Reason being that in weak stratas , a slight rotation of footing result in compatibility moment to cease in case tie beams are not there.

However in manual analysis , for  medium/weak soils , the support condition pinned for Gravity loads And Fixed for EQ/wind  (in case found tie beams not provided). But in softwares only one support condition to be given.

RAFT FOUNDATION - FIXED
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pvgraju
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PostPosted: Fri Jun 10, 2022 5:26 am    Post subject: Support conditions for analyzing G+1 Building Reply with quote

Dear Sir,

Columns resting on raft, piles raft ,isolated footings on hard soil can be treated as fixed.

Isolated footings resting on soft soil are pinned. But instead of treating as pinned springs can be assigned based on soil stiffness for more reliable values.

Regards,

P.V.Gavarraju.
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logeshcivil
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Joined: 07 Aug 2017
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PostPosted: Fri Jun 10, 2022 6:59 am    Post subject: Reply with quote

Dear sir

Can you specify the support conditions based on safe bearing capacity of soil?


vikram.jeet wrote:
Buildings - support condition
Isolated footings resting on Rock  / Hard strata. - Fixed

Isolated footings resting on medium/ weak soils -
With foundation tie beams - Fixed
Without foundation tie beams - Pinned


Reason being that in weak stratas , a slight rotation of footing result in compatibility moment to cease in case tie beams are not there.

However in manual analysis , for  medium/weak soils , the support condition pinned for Gravity loads And Fixed for EQ/wind  (in case found tie beams not provided). But in softwares only one support condition to be given.


RAFT FOUNDATION - FIXED

_________________
Yours
Er. S.Logesh
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vikram.jeet
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PostPosted: Fri Jun 10, 2022 9:41 am    Post subject: Reply with quote

SBC  less than 7.5 T/m2  - is weak strata

SBC of 7.5 to 12 T/m2 is medium strata

SBC  of 12 to 18  T/m2 or more Hard strata

Just to say

However as per NBC , strata with N values for cohesion less soils  as well as ucs values for cohesive soils are classified in these categories and  can be referred.
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vikram.jeet
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PostPosted: Fri Jun 10, 2022 10:05 am    Post subject: Reply with quote

Cohesion less soils :

SPT N value  less than 10  - - Soft Soils

SPT N value 10 to 30 - -  Medium soils

SPT N value greater than 30 - - - HARD SOIL / ROCK

As per NBC
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vikram.jeet
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PostPosted: Fri Jun 10, 2022 3:15 pm    Post subject: Re: Support conditions for analyzing G+1 Building Reply with quote

pvgraju wrote:
Dear Sir,

Columns resting on raft, piles raft ,isolated footings on hard soil can be treated as fixed.

Isolated footings resting on soft soil are pinned. But instead of treating as pinned springs can be assigned based on soil stiffness for more reliable values.

Regards,

P.V.Gavarraju.



Yes , very apt  answer from Er PV Gavarraju .
It will give best results .
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