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reinforcement percentage in column

 
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Vaishali Kulkarni
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Joined: 20 Sep 2013
Posts: 3

PostPosted: Fri Sep 20, 2013 11:52 am    Post subject: reinforcement percentage in column Reply with quote

If percentage of steel in column varies according to the position of column in building? cause it affects modification factor?
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rajancivildesign@gmail.co
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Joined: 26 Jan 2011
Posts: 563

PostPosted: Sat Sep 21, 2013 8:02 am    Post subject: Column Loads Reply with quote

The column load various with postion, grid size and intended use. For example the internal column carries 100%  grid area, side column carries 50% of grid area and corner column carries 25% of grid area. As per moment is concerned, internal column will be designed for minimum eccentricity, side column for uniaxial moment (about 10% of axial load) and corner column for biaxial moment (about 20 to 30% of axial load capacity). In prcatice the load on column carry varied with position and intended use. For internal column , it will be 1.5t/m2, side column 2.0 t/m2 and for corner column 2.5t/m2 per floor for office use. Because of load variation in column, we need not worry about modification factor. It is applicable only to find depth of slab and beam and not on column.
V.M.RAJAN.
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Vaishali Kulkarni
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PostPosted: Sat Sep 21, 2013 11:04 am    Post subject: Reinforcement in column Reply with quote

Thank u so much sir.
But in column designing, (as per thumb rule) we are taking some % of steel.... so what is the ratio for column positioning at different positions?
i.e for eg.   for corner =1% , internal column =1% etc..
plz. elaborate?
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rajancivildesign@gmail.co
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PostPosted: Sat Sep 21, 2013 1:24 pm    Post subject: Column design-allowance for moment Reply with quote

First calculate the load on column on tributary area method.
Load on column= (tributary area x No, of floors x Load/m2).
Add some allowance for bending moment due to effect of fixity between beam and column.
This will be vary from designer to designer. Normally for uniaxial bending it is 15& and for biaxial bending it is 33%.
Equivalent  axial load = Load on column as per tributary area+ % allowance for fixity + % allowance for slenderness ( on axial load + fixity)
The allowance for slenderness in %
Reduction coefficient Cr= 1.25- leff/48b
                                     =1.25 - ((leff/b)/48
allowance for slenderness in % = (1/Cr -1) x 100.
For l/D =15 Cr=0.94 . Allowance for slenderness in %=7.
It is approximate and quick to decide column adequacy.
V.M.RAJAN
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