**How to calculate axial load carrying capacity of column**

**Ultimate load carrying capacity of column**

◆ **introduction** :- 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. 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.

**(Q1) 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**

**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

**1) what is fck**

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**

**2) 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.