Rule of Thumb for RCC Design

Fire resistance (hrs)

Minimum beam width (mm)

Minimum thickness of floors (mm)

Minimum wall thickness (p<0.4%)

Min wall thickness (0.4%

Min wall thickness (p>1%)

0.5

200

75

150

100

75

1

200

95

150

120

75

1.5

200

110

175

140

100

2

200

125

-

160

100

3

240

150

-

200

150

4

280

170

-

240

180

Source: Concrete Centre

Reinforcement for beams

●     Spacing

The minimum spacing of steel reinforcement bars is

1.    Maximum size of coarse aggregate plus 5mm

     Or

     2.   Bar size(whichever is greater)

 

●     Number of bars

Max bars per layer for beams = (beam width – 2 x cover – 2 x link diameter)/(2 x bar diameter)

 

●     Size of bars

Beam width (mm)

Bar diameter (assuming 35mm cover)

 

25

32

40

300

3

3

2

350

4

3

3

400

5

4

3

450

6

5

4

500

7

5

4

550

8

6

5

600

9

7

6

650

10

8

6

700

11

9

7

750

12

10

8

800

13

10

8

900

15

12

9

1000

17

13

11

Source: Concrete Centre

●     Areas of reinforcement

Max of tension or compression reinforcement is 6% of cross sectional area of concrete

Min percentages are shown in the table below, which is Table 3.25 of BS 8110

Picture

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●     Shear Links

Shear links should be spaced no more than 0.75d. No longitudinal bars should be spaced more than 150mm or d from a vertical leg. Shear links should follow the following requirements:

Bar diameter (mm)

16

20

25

32

40

Max spacing (mm)

192

249240

300

384

480

Min link diameter (mm)

6

6

8

8

10