Design of RCC beams./Basic rules for the design of beams./ Basic rules to calculate beam dimension as per IS-456.

 Let us go through the basic rules for the design of beams as per IS456-2000.

1. Beam dimension:

a) Effective depth: The minimum effective depth of the beam can be taken as 1/10th. of the clear span of the beam.

b) Breadth: The minimum required breadth should be between 1/2 to 2/3 of the total depth of the beam.

Eg:

If the span of the beam is 5000mm. ( as shown above), 

The effective depth  d = [1/10 × 5000mm.]

                                   = 500mm.

If the effective cover of the beam is 40mm.,

Beam depth D = [effective depth + effective cover]

                        = [ 500mm. + 40mm.]

                     D   = 540mm.

The minimum breadth b = [1/2 × 540mm.]

                                     b = 270mm.

2. Beam reinforcement:

a) Minimum reinforcement:

The minimum area of tensile reinforcement should not be less than as calculated by the formula

As = 0.85bd / fy

Where, 

As = minimum area of tensile reinforcement.

 b = breadth of beam.

d = effective depth of the beam.

fy = characteristic yield strength of steel.

b) Maximum reinforcement:

The maximum area of reinforcement should not be more than 0.04bD.

Eg:

If fy of steel = 415, 

Minimum reinforcement

As = [0.85bd / fy]

      = [( 0.85 × 270mm. × 500mm.) ÷ 415]

      = 276.50 mm²

     (Beam dimension is taken from Eg-1.)

Maximum reinforcement

= 0.04bD

 = [0.04 × 270mm. × 540mm.]

= 5832 mm².

 3. Side face reinforcement:

If the depth of the beam exceeds 750mm., side face reinforcement should be provided along with the vertical faces on either side of the beam.

The total area of reinforcement should not be less than 0.1% of the web area of the beam. Spacing between the bars should not exceed 300mm.

4. Spacing of reinforcement:

The vertical & horizontal spacing of reinforcement is covered in detail in a separate article as linked below.

👀.  What should be the minimum distance between reinforcement bars?

5. Deflection control:

The vertical deflection limit of the beam should not be more than the values given below.

a) For span up to 10m:

Cantilever beam: The ratio between span/effective depth should be ≤ 7

Simply supported beam: The ratio between span/effective depth should be ≤ 20

Continuous beam: The ratio between span/effective depth should be ≤ 26

b) For spans above 10m.:

The ratio of span/effective depth obtained above should be multiplied by 10/span in m.

To go through all types of structural design articles, click here.

Thank you for going through these calculation steps❤. Have a good day 😄.

        

 

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