# Column size for 6m span and Column design Thumb rule

Column size for 6m span and Column design Thumb rule, size of column depend on total load applied on the column, alignment of column and span between two column, in this topic we try to find out column size for 6m span.

The size of the columns depends on the total load on the columns. There are axial loads and lateral loads.

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Column size depends on various factors like number of floors, span between two column, is it short or slender, For 6m span 1 storey/single floor/ground floor/G+0 residential building, it could be 230mmx230mm (9″×9″), for G+1 it could be 300mmx 300mm (12″×12″), for G+2 it could be 300mmx 380mm (12″×15″),for G+3 it could be 380mmx 450mm (15″×18″) and for G+4 it could be 380mmx 530mm (15″×21″) using M20 grade of concrete ratio 1:1.5:3 with Fe500 grade of steel when a tributary area 18m×18m and span between each column is 6m consists of 16 column.

IS 456:2000 recommendation for designing of column
1) minimum clear cover for column 40mm is provided, if size of column is less than 200mm then clear cover is 25mm is provided.

2) minimum diameter of bar 4 nos of 12mm should be taken

3) minimum area of Steel =0.8%of Ag
Maximum area of Steel=6%of Ag ( Steel should not overlap) 4%of Ag if steel is overlap

4) maximum spacing between two longitudes renforcement shall not greater than 300 mm

5) minimum dia of Stirrup 1/4×16 greater

6) maximum spacing of stirrup 16D, B and 300mm which ever is minimum.

Column size for 6m span for 1 storey/single floor/Ground floor/G+0 residential building:-

1) Calculating column size for 6m span for 1 storey/single floor/ground floor/G+0 residential building, we have given number of floor=1, slab span= 18m ×18m, total number of column = 16, fy=500N/mm2, fck=20N/mm2, thumb rule load=20kN/m2, gross area Ag =100%, steel area Asc =1%ofAg =0.01Ag and concrete area Ac =99%of Ag =0.99Ag.

Load = 1×20kN/m2 ×18m×18m = 6480kN,
Load acting on each column=6480kN/16=405kN, consider 10% increasing load on each column for safety factor, 10% of 405 =40kN, so total axial load acting on each column=405+40= 445kN, putting this value in in formula,

Pu=0.4fck.Ac + 0.67fy.Asc,

445kN=0.4 ×20×0.99Ag + 0.67×500×0.01Ag

445×10^3 = 7.92Ag +3.35Ag

445×10^3 = 11.27Ag

Ag (Gross area=445×10^3/11.27=39485mm2,
Suppose we square column, so area of square =a2, hence a2 = 39485mm2, a=√39485mm2=198mm, width and depth of column =198mm×198mm, taking in round figure=230mm×230mm(9″×9″).

According to column design and Thumb Rule, minimum column size for 6m span is 230mm×230mm (9″×9″) for 1 storey/single floor/ground floor/(G+0) residential building using M20 grade of concrete ratio (1:1.5:3) with Fe500 grade of steel when axial load 445kN is applied on each column.

Column size for 6m span for 2 storey/two floor/G+1 residential building:-

2) Calculating column size for 6m span for 2 storey/two floor/G+1 residential building, we have given number of floor=2, total number of column = 16, span area=18m×18m, fy=500N/mm2, fck=20N/mm2, thumb rule load=20kN/m2, gross area Ag =100%, steel area Asc =1%ofAg =0.01Ag and concrete area Ac =99%of Ag =0.99Ag.

Load = 2×20kN/m2 ×18m×18m = 12960kN,
Load acting on each column=12960kN/16=810kN, consider 10% increasing load on each column for safety factor, 10% of 810 =81kN, so total axial load acting on each column=810+81= 891kN, putting this value in in formula,

Pu=0.4fck.Ac + 0.67fy.Asc,

891kN=0.4 ×20×0.99Ag + 0.67×500×0.01Ag

891×10^3 = 7.92Ag +3.35Ag

891×10^3 = 11.27Ag

Ag (Gross area=891×10^3/11.27=79059mm2,
Suppose we square column, so area of square =a2, hence a2 = 79059mm2, a=√79059mm2=281mm, width and depth of column =281mm×281mm, taking in round figure=300mm×300mm(12″×12″) for rectangular column.

According to column design and Thumb Rule, minimum column size for 6m span is 300mm×300mm (12″×12″) for 2 storey/two floor/(G+1) residential building using M20 grade of concrete ratio (1:1.5:3) with Fe500 grade of steel when axial load 891kN is applied on each column.

Column size for 6m span for 3 storey/three floor/G+2 residential building:-

3) Calculating column size for 6m span for 3 storey/three floor/G+2 residential building, we have given number of floor=3, total number of column = 16, span area=18m×18m, fy=500N/mm2, fck=20N/mm2, thumb rule load=20kN/m2, gross area Ag =100%, steel area Asc =1%ofAg =0.01Ag and concrete area Ac =99%of Ag =0.99Ag.

Load = 3×20kN/m2 ×18m×18m = 19440kN,
Load acting on each column=19440kN/16=1215kN, consider 10% increasing load on each column for safety factor, 10% of 1215 =121kN, so total axial load acting on each column=1215+121= 1336kN, putting this value in in formula,

Pu=0.4fck.Ac + 0.67fy.Asc,

1336kN=0.4 ×20×0.99Ag + 0.67×500×0.01Ag

1336×10^3 = 7.92Ag +3.35Ag

1336×10^3 = 11.27Ag

Ag (Gross area=1336×10^3/11.27=118544mm2,
Suppose we square column, so area of square =a2, hence a2 = 118544mm2, a=√118544mm2=344mm, width and depth of column =344mm×344mm, taking in round figure=300mm×380mm(12″×15″) rectangular column.

According to column design and Thumb Rule, minimum column size for 6m span is 300mm×380mm (12″×15″) for 3 storey/three floor/(G+2) residential building using M20 grade of concrete ratio (1:1.5:3) with Fe500 grade of steel when axial load 1336kN is applied on each column.

Column size for 6m span for 4 storey/four floor/G+3 residential building:-

4) Calculating column size for 6m span for 4 storey/four floor/G+3 residential building, we have given number of floor=4, total number of column = 16, span area=18m×18m, fy=500N/mm2, fck=20N/mm2, thumb rule load=20kN/m2, gross area Ag =100%, steel area Asc =1%ofAg =0.01Ag and concrete area Ac =99%of Ag =0.99Ag.

Load = 4×20kN/m2 ×18m×18m = 25920kN,
Load acting on each column=25920kN/16=1620kN, consider 10% increasing load on each column for safety factor, 10% of 1620 =162kN, so total axial load acting on each column=1620+162= 1782kN, putting this value in in formula,

Pu=0.4fck.Ac + 0.67fy.Asc,

1782kN=0.4 ×20×0.99Ag + 0.67×500×0.01Ag

1782×10^3 = 7.92Ag +3.35Ag

1782×10^3 = 11.27Ag

Ag (Gross area=1782×10^3/11.27=158118mm2,
Suppose we square column, so area of square =a2, hence a2 = 158118mm2, a=√158118mm2=397mm, width and depth of column =397mm×397mm, taking in round figure=380mm×450mm(15″×18″) for rectangular column.

According to column design and Thumb Rule, minimum column size for 6m span is 380mm×450mm (15″×18″) for 4 storey/four floor/(G+3) residential building using M20 grade of concrete ratio (1:1.5:3) with Fe500 grade of steel when axial load 1782kN is applied on each column.

Column size for 6m span for 5 storey/five floor/G+4 residential building:-

5) Calculating column size for 6m span for 5 storey/five floor/G+4 residential building, we have given number of floor=5, total number of column = 16, span area=18m×18m, fy=500N/mm2, fck=20N/mm2, thumb rule load=20kN/m2, gross area Ag =100%, steel area Asc =1%ofAg =0.01Ag and concrete area Ac =99%of Ag =0.99Ag.

Load = 5×20kN/m2 ×18m×18m = 32400kN,
Load acting on each column=32400kN/16=2025kN, consider 10% increasing load on each column for safety factor, 10% of 2025 =202kN, so total axial load acting on each column=2025+202= 2227kN, putting this value in in formula,

Pu=0.4fck.Ac + 0.67fy.Asc,

2227kN=0.4 ×20×0.99Ag + 0.67×500×0.01Ag

2227×10^3 = 7.92Ag +3.35Ag

2227×10^3 = 11.27Ag

Ag (Gross area=2227×10^3/11.27=197604mm2,
Suppose we square column, so area of square =a2, hence a2 = 197604mm2, a=√197604mm2=444mm, width and depth of column =444mm×444mm, taking in round figure=380mm×530mm(15″×21″) for rectangular column.

According to column design and Thumb Rule, minimum column size for 6m span is 380mm×530mm (15″×21″) for 5 storey/five floor/(G+4) residential building using M20 grade of concrete ratio (1:1.5:3) with Fe500 grade of steel when axial load 2227kN is applied on each column.