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

     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