Code of Practice for Bending and Fixing of Bars for Concrete Reinforcement
1963 Edition

Per IS 2502 Clause 3.2.1 and Table II, hook and bend allowances vary according to steel type and bar diameter (d). Hook allowance (H) is calculated as H = k × d, where k ranges from 9 to 17 depending on steel grade and bend complexity, with a minimum of 75 mm rounded to the nearest 5 mm. Bend allowance (B) is B = k × d, with k between 5 and 7, similarly rounded and minimum 75 mm. For example, mild steel bars have hook allowance around 9d and bend allowance near 5d. Internal bend radii should comply with standards, usually at least 6 times the diameter for bends and 4 times for hooks.

IS 2502 mandates measuring bending dimensions along the bar's centerline using standard dimensioning methods outlined in Tables II to IX. For standard bar shapes, dimensions include straight lengths plus hook (H) and bend (B) allowances. Non-standard or combined shapes must be fully dimensioned with clear instructions on measurement methods. Hooks bent out of the plane are to be marked as 'hook up' or 'hook down'. The bending schedule should detail bar mark, size, quantity, length, and shape dimensions to ensure uniformity and clarity in fabrication.

IS 2502 states that bars to be bent have the same cutting tolerances as straight bars, requiring at least one dimension of bent bars to remain unfixed to accommodate this (Clause 5.1.2). Bending tolerances for overall and internal dimensions are specified in Table XI, typically ±10 mm for overall lengths and ±5 mm for internal dimensions. Bars bent to radii exceeding Table X values can be curved during placement instead of physically bent.

According to IS 2502, bars with diameters up to 12 mm are bent using hand-operated mechanical tools like claw-type benders. Bars up to 16 mm can be bent with simple hand bar-bending machines. Bars larger than 16 mm but less than 36 mm are bent with geared machines. For bars 36 mm and above, power-operated bending machines are recommended. For small quantities or simple bends, tools like jim-crow or rail benders may be used.

IS 2502 advises placing reinforcement exactly according to design drawings and securing bars firmly using annealed binding wire of at least 0.90 mm diameter. Ties should be provided based on the number of bars in a set to prevent distortion, with specific counts per number of bars (e.g., one tie for four bars, increasing accordingly). For large vertical bars, timber frames may be used to prevent displacement. Ties should be arranged uniformly or staggered to ensure stability until concreting is complete.