How to calculate axial load carrying capacity of column

How to calculate axial load carrying capacity of column, ultimate load carrying capacity of column, in this topic we know about how to calculate axial load carrying capacity of column. Axial load depends on type of reinforcement used in column and size of column.

Axial load is structural load that is beam slab and brick wall that’s acts on longitudinal axis on column. Axial loading of column means load is acting on longitudinal axis of column this produces no any moment.

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When load is not acting on longitudinal axis of column it will produce bending moment. If bending moment is takes place in only one axis on column than it will be unaxial load and if bending moment is takes along two axis acting on column than it will be biaxial load.

But in this calculation we only calculate axial load carrying capacity of column.

•  determine axial load carrying capacity of rectangular column having size 300× 400 mm and reinforced with 6 nos of Steel bar of 20 mm dia and grade of concrete is M20 and steel is Fe415.

How to calculate axial load carrying capacity of column

◆Given :-
Size of rectangular column = 300mm×400 mm

Grade of concrete = M20

fck = characteristics of comprehensive strength of concrete = 20 N/mm2

Grade of steel = Fe415

fy = yield strength or ultimate tensile strength of Steel = 415 N/mm2

Number of steel bar = 6 nos

Diameter of Steel bar = 20 mm

axial load carrying capacity of column formula

Pu = 0.4fck.Ac + 0.67fy.Asc

as per IS code 456 2000

Where Pu = ultimate axial load carrying capacity of column

fck = characteristics of comprehensive strength of concrete which is given

Ac = area of concrete in column which will be calculated

Asc = area of Steel in column which will be calculated

So we have to following find the value

1) Ac = ? Area of concrete

2) Asc = ? Area of steel

3) Pu = ? Axial load carrying capacity

◆ Solve

1) first we have to calculate gross cross sectional area of column

Ag = gross cross sectional area of column

Size of column = 300×400 mm

Ag = 300×400 mm2

Ag = 120000 mm2

2) second we have to calculate area of Steel in column

Asc = area of Steel in column

No. of steel bar = 6 nos

Diameter of Steel bar D = 20 mm

Area of bar = 6×π/4× D2

Where π = 3.14

Asc = 6× (3.14/4) 20×20 mm2

Asc = 1884 mm2

3) now we calculate area of concrete in column

Ac = area of concrete in column

We know that gross cross sectional area of column is equal to area of concrete in column and area of Steel in column

Ag = Ac + Asc

Ac = Ag _ Asc

Putting the value of gross area of column and steel area subtracting both we get concrete in column

Ac = 120000_1884 mm2

Ac = 118116 mm2

Putting all the value in formula for ultimate axial load carrying capacity of column

Pu = 0.4fck.Ac + 0.67fy.Asc

Where , fck = 20 N/mm2

Ac = 118116 mm2

fy = 415 N/mm2

Asc = 1884 mm2

Pu = (0.4× 20×118116) N +(0.67×415×1884) N

Pu = 944928 N + 523846 N

Pu = 1468774 N

Converting into kilo Newton we have to divide by 1000

Pu = 1468774 N/1000 =1468.774 KN

Hence about 1468.774 KN ultimate axial load carrying capacity of column for above this calculation.

Load carrying capacity of column

Load carrying capacity of column will depend upon the percentage of steel reinforcement, grade of concrete and column size for various mixes and steel.

For steel grade fy 415

Concrete grade & Axial Load carrying Capacity of column in KN (P)

M15, P= (2.7205 p + 6) b D/1500

M20, P= (2.7005 p + 8) b D/1500

M25, P= (2.6805 p + 10) b D/1500

M30, P= (2.6605 p + 12) b D/1500

M35, P= (2.6405 p + 14) b D/1500

M40, P= (2.6205 p + 16) b D/1500

For steel grade fy 500

Concrete grade & Axial Load carrying Capacity of column in KN (P)

M15, P= (3.29 p + 6) b D/1500

M20, P= (3.27 p + 8) b D/1500

M25, P= (3.25 p + 10) b D/1500

M30, P= (3.23 p + 12) b D/1500

M35, P= (3.21 p + 14) b D/1500

M40, P= (3.19 p + 16) b D/1500

For steel grade fy 550

Concrete grade & Axial Load carrying Capacity of column in KN (P)

M15, P= (3.625 p + 6) b D/1500

M20, P= (3.605 p + 8) b D/1500

M25, P= (3.585 p + 10) b D/1500

M30, P= (3.565 p + 12) b D/1500

M35, P= (3.545 p + 14) b D/1500

M40, P= (3.525 p + 16) b D/1500

Note :-

1. The axial Load carrying capacity column is arrived based on the formula

Pu =0.4 fck Ac + 0.67 fy Asc as per IS 456-2000.

2. Here in the Table P is Axial Load Carrying capacity of column in KN.

p is steel in percentage say percentage as 1

b is breadth of column in mm

D is depth of column in mm.

For preliminary design use square columns.

If the building height is 3 stories or less:

If beam span < 6000mm, h (mm) = 300

If 6000 < beam span < 9000, h = 350

If 9000 < beam span < 12000, h = 400

If the building height is 4 to 9 stories:

If beam span < 6000mm, h (mm) = 400

If 6000 < beam span < 9000, h = 500

If 9000 < beam span < 12000, h = 600

1) calculate self load of column

2) calculate self load of beam per metre

3) calculate slab load per square metre

4) calculate dead load of brick wall per metre

5) ultimate load carrying capacity of column

Now we have to few things remember

what is fck in concrete?

It is comprehensive strength of concrete define as characteristics comprehensive strength of 150 mm cube size in 28 days. in designing process 5% of specimen tested are expected to fail if more than 5% of specimen is fail is said to be fail under the test result.

suppose we have 100 cube of 150 mm size of M20 grade 95 cube should be able to with stand a comprehensive load of 20 Newton per mm square if not more than 5% fail than grade of M20 of concrete design is said to be pass under the test result.so fck is characteristics of comprehensive strength of concrete like that for M20and M25 fck is 20N/mm2 and 25N/mm2 respectively.

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You should also visits:-

1)what is concrete and its types and properties

2) concrete quantity calculation for staircase and its formula

3) how to calculate weight of mild steel plate and derive its formula

what is fy in steel

It is yield strength and ultimate tensile strength of various types of Steel denoted by fy steel have many grade like Fe250,Fe415,Fe500 and Fe 250 is low yield strength present in mild steel and Fe415 Fe500 have high yield strength used in formation of column.