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Gravity columns as per IS 13920

 
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rajsen
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PostPosted: Sat Aug 26, 2017 12:09 am    Post subject: Gravity columns as per IS 13920 Reply with quote

As per IS 13920-2016, gravity columns are columns which can be considered as not being part of the lateral load resisting system. It is sufficient to design such columns as gravity load resisting columns at R times lateral displacements under corresponding earthquake loads (Clause 11)


My question is, do the minimum sizing requirements as per Cl 7.1.1 ( max of 20db or 300mm) apply to gravity columns also?

Regards,
Rajarshi Sengupta
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Dr. N. Subramanian
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PostPosted: Mon Aug 28, 2017 4:42 pm    Post subject: Re: Gravity columns as per IS 13920 Reply with quote

Dear Er. Sengupta


For gravity columns it is not necessary to apply minimum sizing as per IS 13920, but we need to follow IS 456.

Best wishes
NS
rajsen wrote:
As per IS 13920-2016, gravity columns are columns which can be considered as not being part of the lateral load resisting system. It is sufficient to design such columns as gravity load resisting columns at R times lateral displacements under corresponding earthquake loads (Clause 11)


My question is, do the minimum sizing requirements as per Cl 7.1.1 ( max of 20db or 300mm) apply to gravity columns also?

Regards,
Rajarshi Sengupta
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sathyace
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PostPosted: Tue Aug 29, 2017 11:16 pm    Post subject: Reply with quote

Dear Sir,

Most of the G+2,G+3 structures are designed with the column width of 150mm in order to meet the architectural requirement,eventhough we face more practical difficulties.

Is there any guidelines to avoid 150mm width column? or is it ok to provide 150mm width column?

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Sathya.
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Dr. N. Subramanian
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PostPosted: Tue Aug 29, 2017 11:29 pm    Post subject: Reply with quote

Dear Er. Sathya


The minimum width of column should be 230 mm.  In earthquake prone areas, it was 300mm but the present IS 13920 stipulates that the minimum size of column should be based on the size of reinforcement.

150 mm columns should never be adopted even for single storey buildings. I do not know from where 150 mm was selected. I have given 230 mm because the column will merge with brick walls.

Best wishes
Subramanian

sathyace wrote:
Dear Sir,

Most of the G+2,G+3 structures are designed with the column width of 150mm in order to meet the architectural requirement,eventhough we face more practical difficulties.

Is there any guidelines to avoid 150mm width column? or is it ok to provide 150mm width column?

Regards,
Sathya.
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sathyace
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PostPosted: Thu Aug 31, 2017 12:22 am    Post subject: Reply with quote

Thank you sir for the valuable reply.

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Sathya.
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lachuman_dhungyel
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PostPosted: Thu Aug 31, 2017 9:55 am    Post subject: Gravity columns as per IS 13920 Reply with quote

Dear sir,     You are requested to design the building frame considering earthquake based on its severity. We can not say whether 150 mm column or some other dimensions is good enough for G+2, or G+3 RCC building frame. I guess we are required to use engineering knowledge and never things on assumptions. Many a times we depend with rule of thump but the engineer should be aware and cross-check it while using the data. Till date I am not aware that 150 mm columns are also used and proved to withstand external loads/dead load. 

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rajsen
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PostPosted: Fri Sep 01, 2017 12:36 am    Post subject: Reply with quote

Thank you Dr. Subramanian.

Thank you Er. Sathya and Er. Lachuman for the insights regarding minimum column dimensions.

I have a further query regarding calculation of additional moments due to gravity loads.

Conceptually, what I understand is that the main columns, due to their ductile behavior, can sustain R times the earthquake load considered in analysis. Therefore, at the time of design earthquake, the gravity columns, although not participating in resisting lateral forces, will be subjected to R times delta coming from earthquake analysis cases. This leads to development of secondary moments due to vertical loads. Please correct me if I am wrong.

My question is, can we consider that gravity columns already have some minimum ductility, say R1=3, and main structure, as per 13920 has R=5. Therefore, can we design the gravity columns for a lesser displacement, say (R-R1)*delta?

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Rajarshi Sengupta
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ashishphadke
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PostPosted: Tue Oct 17, 2017 11:55 am    Post subject: Gravity columns as per IS 13920 Reply with quote

Dear Sirs,

Minimum dimension of column as per 13920-2016, is 300 or 20d,whichever is larger. This is for zone 3, 4 & 5. One should not deviate from it,for any reasons, architectural or commercial...

Is assuming it as gravity column, need to follow clause 11 of13920-2016 in total.

Thanks

Ashish Phadke <o></o>
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Kumar_Abhishek_Singh
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PostPosted: Thu Oct 26, 2017 3:53 am    Post subject: Reply with quote

This is what I know about Gravity columns:

1. They will take the share of lateral loads

2. They should not yield, i..e., remain elastic up to maximum EQ force.

3. Yielding should occur in shear walls nearby.

4. They will be designed for R=1.

5. It is very rare that the columns take very very less lateral loads...computer models may show this but practically doesn't happen hence ductile detailing in gravity columns is required in any case.

6. Gravity column clauses in 13920, to me, are very impractical. I don't know what the code committee was thinking.. may be something beyond my intelligence.

Abhishek
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