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Initial size of column

 
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ramu_se
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Joined: 30 Oct 2017
Posts: 22

PostPosted: Wed Sep 09, 2020 12:10 pm    Post subject: Initial size of column Reply with quote

Dear All,

Kindly guide me how to decide the initial size of the columns before starting the analysis of the structure?

We have to assume the column size according to the thumb rule?

if yes,which is the correct thumb rule to fix initial size of the columns?

Thanks& Regards,
Ramu.
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mjnasar
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Joined: 26 Jan 2003
Posts: 57

PostPosted: Thu Sep 10, 2020 1:46 pm    Post subject: Reply with quote

Dear Eng.Ramu_se

Simple method

calculate tributary area ( load contributing area on column )

X  

1.4 ( Dead load = 5kn/m2  ) + 1.6 ( live = 2 kn/m2 )

= LOAD P

By formula P = 0.80 * fc'*Ac  + 0.9 * fy * Ast

we can derive :

Area of column = P / 25  For middle column
                          P  /20   For Corner column

I hope it will be usefull for you

regards
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es_jayakumar
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Joined: 24 Nov 2011
Posts: 1360
Location: Cochin

PostPosted: Sat Sep 12, 2020 2:07 pm    Post subject: Reply with quote

Respectable author of RCC design books, Dr. HJ Shah has given me the following guidance in this matter :

Different offices have different thumb rules.
I determine as follows:
Determine the axial loads on some selected distributed columns by area method. Then calculate average load on each column. We have two multipliers. One for framed action and another for earthquake zone.
Framed action: For average span of 5m it is 1.2 and 1.4 for 7.5m spans, linearly increased.
Earthquake zones: 1.2, 1.3, 1.4 and 1.5 for zones 2 to 5.
For 1000 kN load , 5m average spans in zone 4, the fixtious loadis 1000*1.2*1.4= 1680 KN load. Calculate for all storeys.
Considering 2.5% reinforcement and higher grade concrete determine size for axial load. Procedure be repeated for all storeys reducing concrete mix and % of reinforcement.
This gives good estimates for economical column sizes.
For more than 12 years, I taught this method to the students of Architecture so that they are capable of suggesting sizes of columns in multi-storey buildings.


E S Jayakumar
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