Clause 7.1 specifies the minimum dimensions and reinforcement limits for columns in ductile RC frames. The minimum column dimension is 300 mm for buildings with more than 2 storeys in Zones III, IV, and V (increased from 200 mm in the 1993 edition). Longitudinal reinforcement must be between 0.8% and 4% of gross area, with at least 3 bars on each face. These requirements ensure adequate ductility and confinement capacity.
Key Requirements
•Minimum dimension of a column shall be 300 mm for buildings with more than two storeys in Seismic Zones III, IV, and V
•Minimum dimension for columns in other cases shall not be less than 200 mm
•Shortest cross-sectional dimension shall not be less than 15 times the largest beam bar diameter passing through or anchoring into the column
•Minimum longitudinal reinforcement shall be 0.8% of gross cross-sectional area
•Maximum longitudinal reinforcement shall be 4% of gross cross-sectional area (limited to ensure constructability at lap locations)
•Minimum number of longitudinal bars shall be 4 for rectangular columns and 6 for circular columns
•There shall be at least 3 bars on each face of rectangular columns
•Spacing of longitudinal bars shall not exceed 300 mm along the periphery
Reference Tables
Minimum Column Dimensions per IS 13920:2016
Condition
Minimum Dimension (mm)
Buildings > 2 storeys in Zone III, IV, V
300
Buildings ≤ 2 storeys in Zone III, IV, V
200
Buildings in Zone II (where IS 13920 applies)
200
15 × largest beam bar through joint
Depends on beam bar
The 1993 edition specified 200 mm minimum. The 2016 edition increased this to 300 mm for multi-storey buildings in high seismic zones.
Practical Notes
✓The 300 mm minimum effectively means most columns in Zone III+ buildings will be 300 × 300 mm or larger. For economy, use 300 × 450 or 300 × 600 to match beam widths.
✓The 4% maximum steel is at the section level, but at lap zones the actual steel doubles to 8% — this makes construction very difficult in small columns. Keep working steel around 2-3% to allow practical lapping.
✓With 3 bars per face minimum, a rectangular column needs at least 8 bars (3 on each of 4 faces, with corner bars shared). In practice, 8–12 bars is typical.
Common Mistakes
⚠Using 230 mm or 200 mm columns in buildings with more than 2 storeys in Zone III or higher — the 2016 code mandates 300 mm minimum.
⚠Providing more than 4% steel, making it impossible to place concrete at lap locations where the actual steel area doubles.
⚠Not checking the 15× beam bar diameter rule — a 25 mm beam bar passing through requires the column to be at least 375 mm in the relevant dimension.