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%)
0.52007515010075
12009515012075
1.5200110175140100
2200125160100
3240150200150
4280170240180

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)
 253240
300332
350433
400543
450654
500754
550865
600976
6501086
7001197
75012108
80013108
90015129
1000171311

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)1620253240
Max spacing (mm)192249240300384480
Min link diameter (mm)668810

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