Lecture 1 what is rcc column and its importance
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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.
Lecture 1 what is rcc column and its importance
- 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