Columns are an important structural member that carry compressive loads and bending moments. They are composed of concrete reinforced with embedded steel. Columns make up 11% of a building's weight but must support 100% of the total weight. Reducing column size or number is not advisable. Column alignment and the moment of inertia 'I' value are also important, with a higher I providing more resistance to bending and deflection. Proper casting, curing, and avoiding honeycombing or voids are crucial for column strength.

1. Introduction to Reinforced concrete
Column
and Its Importance
Presented by
H.M.A.Mahzuz
Assistant Professor
Department of Civil and Environmental Engineering
Shahjalal University of Science and Technology,
Sylhet

2. reinforced concrete column
• It a structural member designed to carry (mainly) compressive
load and bending moment,
• composed of concrete with an embedded steel frame to provide
reinforcement.

3. An example
Force placing diagram (kip/ft) BMD (kip-ft)AFD (kip)

4. Load path of a building
• Slab+Wall
• Beam
• Column
• Footing

5. Why Column is Important?

7. Preliminary selection of member
dimensions:
• Wall thickness = 5''
• Story height = 10'
• Slab thickness = 5''
• Beam size: 16.5''x10''
• All (mid+ side+ corner) column size: 15''x15''

8. Load Calculation
No. Items Calculation Load (Kip)
% of
weight
Weight of one
column =
0.15x1.25x1.25x10 = 2.34
1)
Total weight of
columns =
2.34x18 42.12 11
Beam Length = 68.33x3+28.75x6=377.49
2)
Total weight of
beams =
0.15x377.49x(16.5-5)x10/144 45.22 11
3) Slab weight = 0.15x5/12x68.33x28.75 122.78 31
Wall length
(approximately
equals to beam
length for this
plan)=
377.49
4) Wall weight = 0.12x377.49x5/12x10 188.75 47
Total 398.87 100
% of weight of column in a building =42.12/398.87x100 = 11%

9. Therefore it can be said that
• Column is the 2nd most structural member of a
building.
• having only 11% load column has to carry the
100% weight of a building.
• Tendency of reducing column dimension is not
a good practice.
• Tendency of reducing column number is not a
good practice

10. Column Alignment is also very
Important

11. “I” is an important value!
• It is used to determine the state of stress in a section.
• It is used to calculate the resistance to bending.
• It can be used to determine the amount of deflection.
b
h/2
h/2
z
y
y
b/2
b/2
z
h
12
3
bh
Iz

12
3
hb
Iz >
Stronger section

12. Transfer formula
• There are many built-up sections in which the component
parts are not symmetrically distributed about the centroidal
axis.
• To determine the moment of inertia of such a section is to
find the moment of inertia of the component parts about
their own centroidal axis and then apply the transfer formula.
• The transfer formula transfers the moment of inertia of a
section or area from its own centroidal axis to another parallel
axis. It is known from calculus to be:

14. Column Ix=2*1*1*1/12=0.167 ft4
Column Iy=1*2*2*2/12=0.667 ft4
Room Ix=
0.167*4+1*2*(7.5*7.5)*4=451 ft4
Room Iy=
0.667*4+1*2*(12.5*12.5)*4=1253 ft4
Column Ix=1*2*2*2/12=0.667 ft4
Column Iy=2*1*1*1/12=0.167 ft4
Room Ix=
0.667*4+1*2*(7.5*7.5)*4=453 ft4
Room Iy=
0.167*4+1*2*(12.5*12.5)*4=1251 ft4

15. Column Ix=1*1.5*1.5*1.5/12=0.281 ft4
Column Iy=1.5*1*1*1/12=0.125 ft4
Building Ix=0.281*18+1*1.5*(10*10+0*0+10*10)*6=1805 ft4
Building Iy=0.125*18+1*1.5*((25*25+15*15+5*5)*2*3)=7877 ft4

16. Column Ix=1.5*1*1*1/12=0.125 ft4
Column Iy=1*1.5*1.5*1.5/12=0.281 ft4
Building Ix=0..125*18+1*1.5*(10*10+0*0+10*10)*6=1802 ft4
Building Iy=0.281*18+1*1.5*((25*25+15*15+5*5)*2*3)=7880 ft4

17. Which building is better/stronger?
Building Ix=1805 ft4
Building Iy=7877 ft4
Building Ix=1802 ft4
Building Iy=7880 ft4

18. Column
casting

19. Column curing

20. These may occur due to
1) Improper compaction during casting
2) Low W/c ratio

21. Precast Column