Ductile Design and Detailing of Reinforced Concrete Structures Subjected to Seismic Forces —
Code of Practice
The primary standard governing seismic detailing of reinforced concrete structures. Mandatory for buildings in Seismic Zones III, IV, and V, this code prescribes special confinement reinforcement, joint detailing, and ductility requirements to ensure life-safety performance during earthquakes.
📋 Major Revision: The 2016 edition is a comprehensive revision of the 1993 version. It incorporates provisions for shear walls, beam-column joints, and coupling beams that were absent in the earlier edition. Always use the 2016 version for new designs.
IS 13920:2016 applies to the design and detailing of monolithic reinforced concrete structures subjected to seismic forces. Its provisions are mandatory or recommended based on seismic zone:
| Seismic Zone | Applicability | Remark |
|---|---|---|
| Zone V | Mandatory | Highest seismicity — all RC structures |
| Zone IV | Mandatory | High seismicity — all RC structures |
| Zone III | Mandatory | Moderate seismicity — all RC structures |
| Zone II | Recommended | Required when Importance Factor I ≥ 1.5 (hospitals, schools) |
Scope Exclusions The code does not cover prestressed concrete structures, precast elements, or structures with base isolation. For those, specialist provisions apply. Seismic zone classification is per IS 1893 (Part 1).
Beams in seismic frames must satisfy dimensional and reinforcement requirements to ensure adequate ductility and prevent brittle failure modes.
| Requirement | Limit | Clause |
|---|---|---|
| Minimum width (b) | 200 mm | Cl. 6.1.2 |
| Width-to-depth ratio (b/D) | ≥ 0.3 | Cl. 6.1.2 |
| Min. tension steel ratio (ρmin) | 0.24√fck / fy | Cl. 6.2.1(a) |
| Max. tension steel ratio (ρmax) | 2.5% | Cl. 6.2.1(b) |
| Hogging steel at support | ≥ 50% of sagging steel at that section | Cl. 6.2.3 |
| Min. steel at any section (top or bottom) | ≥ 25% of max. steel at either end | Cl. 6.2.3 |
Confinement zones (plastic hinge regions) extend over a length of 2d from the face of the support at each end of the beam. Within these zones, stirrup spacing is the minimum of:
Lap Splice Location Lap splices in beam longitudinal bars shall not be placed within a joint, within 2d from the face of a joint, or at locations of potential plastic hinges. Not more than 50% of bars shall be spliced at one section.
Columns in seismic frames must be designed to be stronger than the beams framing into them (strong-column weak-beam philosophy) and must be provided with Special Confining Reinforcement (SCR) at potential hinge zones.
| Requirement | Limit | Clause |
|---|---|---|
| Minimum dimension | 300 mm | Cl. 7.1.2 |
| Gross area (Ag) | ≥ 0.01 × sum of beam areas framing in | Cl. 7.1.2 |
| Min. longitudinal steel | 0.8% of Ag | Cl. 7.2.1 |
| Max. longitudinal steel | 4% of Ag (6% at lap) | Cl. 7.2.1 |
Special Confining Reinforcement (SCR) zones must be provided at the top and bottom of each column over a length lo:
Within the SCR zone, hoop spacing shall not exceed:
The required cross-sectional area of hoop reinforcement in the SCR zone is:
Strong Column — Weak Beam The sum of moment capacities of columns at a joint must be at least 1.1 times the sum of moment capacities of beams framing into that joint (Cl. 7.2.1). This ensures plastic hinges form in beams, not columns.
Beam-column joints are critical regions where large shear forces develop during seismic events. IS 13920:2016 introduced explicit joint shear design provisions absent in the 1993 edition.
| Joint Type | Description | Confinement Required |
|---|---|---|
| Interior Joint | Beams framing on all four sides | Minimum — beams provide confinement |
| Exterior Joint | Beams on two or three sides | Full SCR hoops through joint depth |
| Corner Joint | Beams on one or two adjacent sides | Full SCR hoops through joint depth |
The nominal joint shear stress τj must not exceed the permissible value:
Transverse Reinforcement Through Joint At least 50% of the column SCR hoops must be continued through the joint. Where beams frame on all four sides and each beam width is at least 75% of the column width, the joint is considered confined and hoop spacing may be relaxed to 150 mm.
Shear walls (structural walls) are the primary lateral-force-resisting elements in many RC buildings. IS 13920:2016 provides comprehensive detailing requirements for ductile shear walls.
| Requirement | Limit | Clause |
|---|---|---|
| Minimum wall thickness | 150 mm | Cl. 9.1.2 |
| Min. reinforcement ratio — each direction | 0.0025 (0.25%) | Cl. 9.1.4 |
| Max. spacing of bars (each direction) | Min (lw/5, 3tw, 450 mm) | Cl. 9.1.4 |
| Two curtains of steel required when | tw ≥ 200 mm or Vu > 0.2fcktwdw | Cl. 9.1.5 |
Boundary elements are required at the extreme fibres of shear walls when the extreme fibre compressive stress under factored loads exceeds 0.2fck. They act as confined columns at the wall edges.
Coupling Beams Coupling beams connecting adjacent shear walls with span-to-depth ratio ≤ 4 shall be provided with diagonal reinforcement. The diagonal bars must be confined with closely spaced hoops. This ensures ductile energy dissipation in the coupling beams during seismic events.
| Topic | IS 13920 : 1993 | IS 13920 : 2016 |
|---|---|---|
| Shear walls | Not covered | Comprehensive Cl. 9 added |
| Beam-column joints | Not covered | Explicit joint shear design in Cl. 8 |
| Coupling beams | Not covered | Diagonal reinforcement provisions added |
| Column min. dimension | Not specified | 300 mm minimum |
| Hoop area formula | Ash formula present | Revised with updated coefficients |
| SCR zone length | max(D, lc/6, 450 mm) | Same — retained |
| Beam width | 200 mm minimum | 200 mm — retained |
Alignment with IS 1893:2016 The 2016 revision was coordinated with the simultaneous revision of IS 1893 (earthquake loads). Both codes now use consistent terminology and zone-based applicability criteria.