IS 13920 : 2016Ductile Design and Detailing of Reinforced Concrete Structures Subjected to Seismic Forces - Code of Practice

IS 13920:2016 specifies ductile design and detailing of reinforced concrete structures subjected to seismic forces. It is mandatory for RCC buildings in Seismic Zones III, IV, and V — either because the structure is required to resist earthquake forces or because the designer has opted for the higher response reduction factor (R = 5 for special moment-resisting frames).

Pair IS 13920 with: - IS 1893 Part 1:2016 — which establishes the seismic demand (base shear) - IS 456:2000 — the parent RCC code which IS 13920 extends with ductile provisions

Typical projects requiring IS 13920 detailing: - All multi-storey RCC buildings in Zones III, IV, V - Ordinary buildings in Zone II if R ≥ 3 is used - Hospitals, schools, fire stations (importance factor I = 1.5 per IS 1893) - Industrial structures in seismic zones - Any structure using R = 5 (special moment-resisting frame) — R = 5 WITHOUT IS 13920 detailing is non-compliant and unconservative by ~40%.

IS 13920:2016 codifies the capacity-based design philosophy through the Strong-Column-Weak-Beam (SCWB) check at every beam-column joint per Clause 7.2.1:

ΣM_c ≥ 1.4 × ΣM_b

Where ΣM_c is the sum of column moment capacities above and below the joint, and ΣM_b is the sum of beam moment capacities framing into the joint. The 1.4 factor ensures columns stay elastic while beams form plastic hinges — critical for preventing soft-storey collapse.

Other key ductile provisions:

Confining hoops in plastic hinge zones (Clause 7.6) — at beam ends and column ends, spacing ≤ d/4 or 100 mm, with 135° hook ends (not 90°) that extend 10d into the confined core.

Minimum column size (Clause 7.1) — square column ≥ 300 mm; circular ≥ 300 mm diameter. Smaller columns are permitted only by derogation with enhanced confinement.

Column splice location (Clause 7.5) — only in the middle half of the column clear height. No splicing in plastic hinge zones (top or bottom quarters of storey height).

Problem: G+4 residential RCC building in Zone IV (Z = 0.24, Delhi-Meerut region). OMRF initially, but user wants to upgrade to special MRF for better seismic performance (R = 5 instead of R = 3).

Base shear reduction (benefit of R = 5 vs R = 3): A_h (R=5) = (0.24/2) × (1/5) × 2.5 = 0.06 A_h (R=3) = (0.24/2) × (1/3) × 2.5 = 0.10 V_B (R=5) = 0.6 × V_B (R=3) — a 40% reduction in design base shear.

But to earn R = 5, the frame must comply with IS 13920 ductile detailing throughout. Let's detail a typical column.

Column 400 × 400 with Fe 500 longitudinal bars:

Step 1 — Minimum size check: 400 > 300 mm ✓ (Clause 7.1)

Step 2 — Longitudinal reinforcement: 0.8% minimum, 6% maximum (IS 13920 Clause 7.4). For 400 × 400, A_st,min = 1,280 mm². Use 8-16 mm bars = 1,608 mm² ✓

Step 3 — Confining hoop design (Clause 7.6.1.2): Plastic hinge zone: 450 mm from face of beam (≥ greater of clear column depth or 1/6 clear height or 450 mm). Hoop diameter: 8 mm (≥ 6 for bar dia ≤ 16) Spacing: ≤ d/4 = 400/4 = 100 mm, also ≤ 6 × 16 = 96 mm (bar diameter × 6), and ≤ 100 mm (absolute max) Use 8 mm hoops @ 75 mm c/c in plastic hinge zone; can space out to 200 mm c/c in middle region.

Step 4 — Hook detailing (Clause 7.6.1.4): 135° hooks on every hoop, 10 × 8 = 80 mm hook extension into confined core. No 90° hooks permitted.

Step 5 — Splice location: Only in middle half (between 1.25 m and 2.5 m for 3.0 m column clear height). No splice in top or bottom 750 mm.

Step 6 — SCWB check at the beam-column joint: Assume M_b,hog = 180 kNm and M_b,sag = 120 kNm (total beam capacity at joint = 300 kNm from two beams). Required column capacity: ΣM_c ≥ 1.4 × 300 = 420 kNm across the two column segments (above + below joint). Use Pu-Mu interaction diagram for 400×400 column with 8-16 bars: typical capacity ~250 kNm per segment = 500 kNm total ≥ 420 ✓

Column passes SCWB. Frame qualifies as special MRF, R = 5 permitted.

1. Using R = 5 without IS 13920 detailing. Most dangerous mistake. Applying R = 5 in IS 1893 base shear calculation requires full IS 13920 compliance. Skipping 135° hooks, confining hoops, or SCWB check while still using R = 5 gives you a design that is ~40% unconservative — the structure has been sized for earthquake forces that assume ductile behaviour it cannot deliver.

2. 90° hooks on stirrups and hoops. IS 13920 Clause 7.6.1.4 requires 135° hooks. 90° hooks straighten and pull out under severe shaking. This is the single most common construction-site compliance issue — and one that's easy to spot in inspection photographs.

3. Splicing columns in the plastic hinge zone. Clause 7.5.1 restricts splicing to the middle half of clear column height. Bar splices concentrate stress; placing them in the plastic hinge zone (top/bottom quarters) defeats the ductile detailing. This is common on sites where labour splices bars wherever the supply lengths run out.

4. Skipping SCWB check. Many designers follow all the detailing rules but never verify Σ M_c ≥ 1.4 × Σ M_b at each joint. Soft-storey collapse is almost always traced to beam capacity exceeding column capacity at a specific joint. This check takes 2 minutes per joint in a design review.

5. Forgetting slab contribution in T-beam moment capacity. IS 13920 Clause 6.1.3 requires you to include the slab flange (effective width) in beam positive moment capacity. Many designers only count the rectangular beam section — this underestimates M_b by 30-50% and may cause the SCWB check to wrongly pass. The beam is actually stronger than calculated, and columns may need to be larger.

• IS 1893 Part 1:2016 — seismic demand side (base shear, zone factor Z, response reduction R)
• IS 456:2000 — parent RCC design code
• IS 1786:2008 — Fe 500D and Fe 550D preferred TMT grades for seismic work (higher elongation than Fe 500)
• IS 13827:1993 — earthquake-resistant construction of low-rise buildings
• IS 4326:1993 — earthquake-resistant construction details for masonry
• IS 1905:1987 — plain and reinforced masonry buildings in seismic zones
• IRC 112:2020 — bridge-specific equivalents of IS 13920 detailing for RCC bridges
• AISC 341 — US seismic detailing standard; often used as supplement for tall buildings, base-isolated structures, or when Indian practice needs broader guidance

IS 13920:2016 is the most technically demanding Indian structural code to implement correctly on site. Amendments (A1 2018, A2 2022) clarified hoop detailing, splice requirements, and SCWB calculation for sloped columns.

Field reality check: many projects in Zone III that claim IS 13920 compliance have 90° hooks in columns from either site labour shortcuts or inherited drawings from the 1993 version (which allowed 90°). If you are doing third-party design review or peer check, inspect site photos for hook angles first — it is the fastest compliance test.

For tall buildings (30+ storeys) in Zone IV and V, IS 13920 alone is conservative but can be supplemented with AISC 341 Chapters E and F for detailed seismic steel-composite detailing not covered in IS 13920's primarily RCC scope.

BIS has a draft revision of IS 13920 circulating within CED 39 since 2023, expected to add explicit provisions for dual system (shear wall + MRF), performance-based seismic design, and composite ductile frames. Watch for public consultation in 2026-2027.

For any residential project above G+4 in Zone IV or V, always specify Fe 500D or Fe 550D TMT per IS 1786 — these grades have higher elongation (16-18%) than Fe 500 (12%) and are mandatory under IS 13920 Clause 6.2.1 for seismic reinforcement.