IRC Bridge Seismic Zones — IRC SP 114 / IRC 6:2017

Seismic design zone classification specifically for road bridges per IRC SP 114:2018 + IRC 6:2017 Cl. 219. Same zone boundaries as IS 1893 Annex E but with bridge-specific design factors, importance categories, and dynamic-analysis triggers.
67
II
74
III
36
IV
20
V
Zone II · Low (Z = 0.10) · Z = 0.10
Zone III · Moderate (Z = 0.16) · Z = 0.16
Zone IV · High (Z = 0.24) · Z = 0.24
Zone V · Severe (Z = 0.36) · Z = 0.36
Loading map…
📍
Click anywhere on the map, or search a city
Try
Click any spot on the map to drop a pin and get the estimated zone. Map data © OpenStreetMap contributors.

Why IRC seismic differs from IS 1893

Bridges have distinct dynamic behavior — long spans, isolated piers, soil-structure interaction over rivers. IRC SP 114 introduces bridge-specific factors: (1) importance factor I = 1.0/1.2/1.5 by bridge class; (2) ductile detailing IRC SP 114 Cl. 8 for piers; (3) dynamic analysis triggers (span > 60 m, skew > 30°, curve, multiple-frame); (4) seismic isolation for Zone V critical bridges.

Analysis methods by zone + span

  • Zone II (Z=0.10): equivalent static for all bridges. Dynamic only for span > 60 m.
  • Zone III (Z=0.16): equivalent static OK for span < 60 m. Ductile detailing piers.
  • Zone IV (Z=0.24): dynamic analysis recommended for span > 30 m. Mandatory ductile detailing.
  • Zone V (Z=0.36): time-history analysis mandatory. Energy-dissipating devices (isolators, viscous dampers) typical for lifeline bridges.

Cross-references

Source IS / IRC / NBC standards

IRC 6:2017Bridge Loads — Cl. 219 seismicIRC 78:2014Bridge Foundations + substructuresIRC 112:2020Concrete Bridge CodeIS 1893 (Part 1)Reference seismic zoning map

Related maps

IS 1893 Seismic ZonesFor buildings (different factors)Wind SpeedBridge wind design also IRC-specificCyclone ZonesCoastal bridges + cyclone factor

Calculators & tools

Beam SelectorSteel composite bridge spans

Articles & guides

IRC 78 Bridge FoundationsComplete guideIRC 112:2020Concrete bridge design

Frequently asked questions

Are IS 1893 and IRC seismic zones the same?

Same zone boundaries (Annex E geographic regions identical). But IRC adds bridge-specific factors: importance factor by class (I = 1.0 for normal, 1.2 for important, 1.5 for lifeline), ductile detailing rules per IRC SP 114 Cl. 8, and dynamic-analysis triggers based on span + skew + curve geometry. IS 1893 covers buildings; IRC covers road bridges.

What is the IRC bridge importance factor I?

Per IRC 6:2017 + IRC SP 114: I = 1.0 for normal bridges (most), 1.2 for important bridges (urban arterial, >2 lanes per direction, > 200 m span), 1.5 for lifeline bridges (national highway, last-bridge-out, post-disaster access). Multiplies design seismic force.

When is dynamic analysis mandatory?

Per IRC SP 114 Cl. 5: mandatory for any bridge in Zone IV/V with span > 30 m, skew > 30°, horizontally-curved spans, multi-frame structures, or with foundation soil class D/E. Zone II/III thresholds are 60 m span, similar geometry triggers. Lifeline bridges always require dynamic analysis.

IRC SP 114 + IRC 6 should be consulted directly for any active bridge design. The map gives the zone boundary; design factors, ductility class, and analysis method depend on bridge class, span, geometry, and foundation soil — not just the seismic zone.

← Back to all engineering maps