Friday, December 30, 2016

Bar Bending Schedule-BBS Civil Engineering Estimation And Casting

Bar bending schedule offers the reinforcement calculation for reinforced concrete beam. It supplies details of reinforcement cutting length, type of bends and bend length.

Here we will take one example for reinforcement quantity calculations for a concrete beam.

Example of RCC Beam Reinforcement Calculation:

Assume a beam of clear length of 4m, 300mm wide by 450mm depth. It consists of 2-12 diameter bars at top, and 2-16 diameter and 1 – 12 diameter bars at the bottom. Diameter of stirrup is 8mm spaced at 180mm center to center. Clear cover to reinforcement provided is 40mm.

Now we will calculate the length of reinforcement on the basis of shapes of reinforcement mandatory for reinforced concrete beam in above example.

Bar shape of B1 is as shown below:

RCC Beam Bar Bending Shape

Length of B1 = clear distance between walls + 2 x width of walls – 2 x bar cover + 2 x bend length

Bend length = 6 x 16 = 96 consider as 100mm

Bend length is calculated as 6 x diameter of bar for reinforcement conforming to IS: 1786-1961

Length of B1 = 4000 + 2 x 230 – 2 x 40 + 2 x100 = 4580mm

Length of bar B2 is calculated on the basis of the shape of this bar. This bar bends up closer to the support as shown below:

RCC Beam Bar Bending Shape

Length of bar B2: A + B + C = 4000 + 2 x 230 – 2 x 40 + (1.414xH – H)

H = 450 – 2 x 40 – 2 x 12 – 2 x 12/2 = 334mm

B2 = 4000 + 2 x 230 – 2 x 40 + (1.414×334 – 334) = 4518.3 = 4520mm

Length of Bar T1 = 4000 + 2 x 230 -2 x 40 = 4380mm

Length of Stirrups S1:

RCC Beam Stirrups Length Calculation

Stirrups are spaced at 180mm center to center. Stirrups are provided between walls or support for a beam.

No. of stirrups required for given beam = No. of Stirrups

Length a = 450 – 2 x40 – 8 = 362mm

Length b = 300 – 2 x 40 – 8 = 212mm

Therefore length of 1 stirrup S1 = 2 x (212 + 362 + 90) = 1328 mm

Where 90mm is the minimum hook length as per IS 2502 – Table – II.

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