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1. Reinforced Concrete Design
ACI Code 318-08

2. Course Outline
1. Properties of Reinforced Concrete
2. Flexural Analysis of Reinforced Concrete Beams
3. Flexural Design of Reinforced Concrete Beams
4. Development Length of Reinforcing Bars
5. Shear and Diagonal Tension
6. Torsion
7. Axially Loaded Columns
8. Members in Compression and Bending
9. Slender Columns
10. One-way Slabs
11. Two-ways Slabs
12. Stairs
13. Footings

3. Chapter 1
Properties of Reinforced Concrete

4. 1. Properties of Reinforced Concrete
1.1 Factor affecting the strength of concrete
1.2 Compressive strength
1.3 Tensile strength of concrete
1.4 Flexural strength (Modulus of rupture) of concrete
1.5 Shear strength
1.6 Modulus of elasticity of concrete
1.7 Steel reinforcement

5. 1.1 Factor affecting the strength of concrete
 Water-cement ratio: for complete hydration
W/C = 0.25 is needed.
 Properties and proportions of concrete
constituents:
• An increase in cement content in the mix increase the
strength of concrete
• Use well-graded aggregate increase the strength of
concrete.
• Special admixtures are usually added to the mix to
produce the desired quality and strength of concrete.
1. Properties of Reinforced Concrete

6. 1.1 Factor affecting the strength of concrete
 Method of mixing and curing: concrete mixer,
proper time of mixing, vibrator, curing (moisture
and temperature). The longer period of moist
storage, the greater the strength.
 Age of the concrete:
1. Properties of Reinforced Concrete
,28
( )
4 0.85
c c
t
f t f
t
 


Age 7
days
14
days
28
days
3
months
6
months
1
year
2
years
3
years
Strength
Ratio
0.67 0.86 1 1.17 1.23 1.27 1.31 1.35

7. 1.1 Factor affecting the strength of concrete
 Loading condition: the compressive strength of
concrete (f’c) is usually obtained from static
loading test, not including dynamic and creep
effects.
 Shape and dimension of tested specimen:
1. Properties of Reinforced Concrete
 
, , ,
0.85 to 0.8 1.1
c cyl c cube c prism
f f f
  
 

8. Relative strength for various size of cylinders
1. Properties of Reinforced Concrete
Size of cylinder (mm) Relative compressive
strength
50 x 100 1.09
75 x 150 1.06
150 x 300 1.00
200 x 400 0.96
300 x 600 0.91
450 x 900 0.86
600 x 1200 0.84
900 x 1800 0.82

10. 1. Properties of Reinforced Concrete
1.1 Factor affecting the strength of concrete
1.2 Compressive strength
1.3 Tensile strength of concrete
1.4 Flexural strength (Modulus of rupture) of concrete
1.5 Shear strength
1.6 Modulus of elasticity of concrete
1.7 Steel reinforcement

11. 1.2 Compressive strength

12. Compressive strength
(30x15)cm cylinder
28 day moist cure
Ultimate (failure) strength
'
c
f

13. 1.2 Compressive strength

14. 1. Properties of Reinforced Concrete
1.1 Factor affecting the strength of concrete
1.2 Compressive strength
1.3 Tensile strength of concrete
1.4 Flexural strength (Modulus of rupture) of concrete
1.5 Shear strength
1.6 Modulus of elasticity of concrete
1.7 Steel reinforcement

15. 1.3 Tensile strength of concrete
Where P compressive load, D and L are diameter and
length of cylinder
Generally,
2
sp
P
f
LD

 
10%
sp c
f f
 


16. Concrete cylinder
splitting test
P
Concrete Cylinder
Poisson’s
Effect

17. 1.4 Flexural strength (Modulus of rupture) of
concrete
0.62 (MPa)
r c
f f
 

 
1.25 1.50 (MPa)
r sp
f to f 


19. 1.5 Shear strength
Where:  is a modification factor for type of
concrete (ACI 8.6.1)
 = 1.0 Normal-weight concrete
 = 0.85 Sand-lightweight concrete
 = 0.75 for all-lightweight concrete
0.17 (MPa)
c
f f
  


20. 1.6 Modulus of elasticity of concrete

21. 1.6 Modulus of elasticity of concrete
In practice, secant modulus at 50% of f’c is used.
Or
c
E



 
1.5 3
0.043 (MPa), = /
c c
E w f w kg m


=4780 (MPa)
c c
E f 

22. Steel Reinforcement
22
Bars are deformed to increase bonding with concrete

23. 1.7 Steel reinforcement

24. 1.7 Steel reinforcement

25. 1.7 Steel reinforcement

26. 1.7 Steel reinforcement
MPa
ksi
276
40
414
60
552
80

27. តារាងមុខកាត់ដែកសសស(សម២)
Diameter Number of Bars
ϕ (mm) 1 2 3 4 5 6 7 8 9 10 12 13 14 15
6 0.28 0.57 0.85 1.13 1.41 1.70 1.98 2.26 2.54 2.83 3.39 3.68 3.96 4.24
8 0.50 1.01 1.51 2.01 2.51 3.02 3.52 4.02 4.52 5.03 6.03 6.53 7.04 7.54
10 0.79 1.57 2.36 3.14 3.93 4.71 5.50 6.28 7.07 7.85 9.42 10.21 11.00 11.78
12 1.13 2.26 3.39 4.52 5.65 6.79 7.92 9.05 10.18 11.31 13.57 14.70 15.83 16.96
14 1.54 3.08 4.62 6.16 7.70 9.24 10.78 12.32 13.85 15.39 18.47 20.01 21.55 23.09
16 2.01 4.02 6.03 8.04 10.05 12.06 14.07 16.08 18.10 20.11 24.13 26.14 28.15 30.16
18 2.54 5.09 7.63 10.18 12.72 15.27 17.81 20.36 22.90 25.45 30.54 33.08 35.63 38.17
20 3.14 6.28 9.42 12.57 15.71 18.85 21.99 25.13 28.27 31.42 37.70 40.84 43.98 47.12
22 3.80 7.60 11.40 15.21 19.01 22.81 26.61 30.41 34.21 38.01 45.62 49.42 53.22 57.02
25 4.91 9.82 14.73 19.63 24.54 29.45 34.36 39.27 44.18 49.09 58.90 63.81 68.72 73.63
30 7.07 14.14 21.21 28.27 35.34 42.41 49.48 56.55 63.62 70.69 84.82 91.89 98.96 106.03
32 8.04 16.08 24.13 32.17 40.21 48.25 56.30 64.34 72.38 80.42 96.51 104.55 112.59 120.64
38 11.34 22.68 34.02 45.36 56.71 68.05 79.39 90.73 102.07 113.41 136.09 147.43 158.78 170.12