IRC 24:2010 is the Indian Standard (IRC) for standard specifications and code of practice for road bridges — steel road bridges. IRC 24 covers design of steel road bridges — plate girders, trusses, and steel components of composite bridges. Based on IS 800 (steel design code) adapted for bridge-specific requirements including fatigue assessment.
Design of steel road bridges including plate girders, truss bridges, and composite steel-concrete bridges using limit state method.
Steel girder bridges — material grades, deflection, fatigue, welding, partial safety factors.
| Reference | Value | Clause |
|---|---|---|
| Structural steel — minimum grade | Fe-410W (E250) | Cl. 504.1 (Table 1) |
| Structural steel — high-strength | Fe-490, Fe-540, Fe-590 | Cl. 504.1 (IS 2062) |
| Yield strength fy — Fe-410W | 250 N/mm² | Cl. 504.1 |
| Yield strength fy — Fe-540W | 410 N/mm² (< 16 mm) | Cl. 504.1 |
| Tensile strength fu — Fe-410W | 410 N/mm² (min) | Cl. 504.1 |
| Modulus of elasticity E | 2.0 × 10⁵ N/mm² | Cl. 504.2 |
| Density of structural steel | 78.5 kN/m³ | Cl. 504.2 |
| Coefficient of thermal expansion α | 12 × 10⁻⁶ /°C | Cl. 504.2 |
| Partial safety factor γm0 (yield) | 1.10 | Cl. 506.2 (Table 1) |
| Partial safety factor γm1 (rupture) | 1.25 | Cl. 506.2 (Table 1) |
| Partial safety factor γm — bolts/welds | 1.25 (shop) / 1.50 (site) | Cl. 506.2 (Table 1) |
| Maximum slenderness λ — main compression | 120 | Cl. 511 (Table 5) |
| Maximum slenderness λ — bracing in tension | 350 | Cl. 511 (Table 5) |
| Effective length factor — pinned-pinned | 1.0 | Cl. 511.4 (Table 6) |
| Effective length factor — fixed-fixed | 0.65 | Cl. 511.4 (Table 6) |
| Deflection limit — live load span (girder) | L/800 | Cl. 510.4 |
| Deflection limit — cantilever live load | L/300 | Cl. 510.4 |
| Camber — built-in for permanent loads— to compensate for long-term creep + permanent load | 1.5 × DL deflection | Cl. 510.5 |
| Fatigue — Class B detail (welded) | Δσ ≈ 80 MPa @ 2×10⁶ cycles | Cl. 514 (Annex G) |
| Welding — minimum throat thickness | 3 mm (≤ 10 mm plate) | Cl. 519.4 (IS 816) |
| Bolt spacing — minimum centre to centre | 2.5 × bolt diameter | Cl. 519.7 |
| Edge distance — sheared edge | 1.7 × bolt-hole diameter | Cl. 519.7 (Table 11) |
IRC 24:2010 is Section V — Steel Road Bridges of the IRC standard specifications. It covers design of all-steel road bridges — truss bridges, plate girder bridges, steel box girders, cable-stayed steel decks, and steel arch bridges.
You use IRC 24 for: - Steel truss bridges (typical 40-200 m span — rail-bridges often use IRC 24 as supplement) - Steel plate girder bridges (20-80 m span) - Steel box girder bridges (40-150 m span) - Steel arch bridges (signature crossings, 60-300 m span) - Fatigue assessment of all steel bridge components
For composite steel-concrete bridges, pair IRC 24 (girder design) with IRC 22:2008 (composite action). For concrete-only bridges, use IRC 112:2020 instead of IRC 24.
IRC 24:2010 is based on limit state design (aligned with IS 800:2007) and updates the older IRC 24:1967 permissible-stress edition. The 2010 edition is still current.
IRC 24:2010 follows Limit State Method with bridge-specific partial safety factors.
ULS partial safety factors: - γ_DL = 1.35 (dead load) - γ_LL = 1.50 (live load, vehicles per IRC 6) - γ_wind = 1.50, γ_seismic = 1.50 - γ_m0 = 1.10 (material, for yielding) - γ_m1 = 1.25 (material, for rupture/buckling)
SLS checks: - Deflection limits: L/600 (dead + live) per Clause 507 - Vibration check for bridges with pedestrian traffic - Fatigue (important for steel bridges — tens of millions of stress cycles over lifetime)
Material specifications: - IS 2062:2011 E350 BR or E450 CR for main members (BR = impact at 0°C, CR = ruggedized impact) - E350 D (impact at -20°C) for cold-climate / high-altitude bridges (Kashmir, NE India) - Welding per IS 816 / IS 9595 or AWS D1.5 - Bolts: HSFG (high-strength friction grip) bolts per IS 3757 for slip-critical connections
Section classification per IS 800 Clause 3.7: - Plastic — full plastic moment developed before local buckling - Compact — plastic moment developed but no rotation capacity - Semi-compact — yielding at extreme fibre, no plastic moment - Slender — local buckling before yield
Steel bridges see 10-100 million stress cycles over their lifetime (each truck passing = one cycle). Fatigue is the governing limit state for many bridge components.
IRC 24 Clause 511 — Fatigue:
Fatigue stress range at each critical detail: Δσ_fatigue = σ_max − σ_min (from one truck passing)
Allowable fatigue stress range f_f from detail category (A through G per IRC 24 Table 17): - Category A (plain rolled section): f_f ≈ 165 MPa for 2 million cycles - Category B (butt welded, full penetration): f_f ≈ 110 MPa - Category C (transverse fillet weld to flange): f_f ≈ 85 MPa - Category D (longitudinal fillet weld at stiffener): f_f ≈ 70 MPa - Category E (web-to-flange fillet weld): f_f ≈ 60 MPa - Category F (stud shear connector weld): f_f ≈ 45 MPa - Category G (critical welded joints): f_f ≈ 35 MPa
Design rule: Δσ_fatigue ≤ f_f adjusted for design cycles
For heavy-traffic bridges, fatigue dictates specific detailing: - Continuous welds (not intermittent) at critical joints - Full penetration butt welds, not fillet welds, where possible - Avoid cope holes and abrupt thickness changes - Smooth grinding of weld toes to reduce stress concentration
Common fatigue-failure locations: - Cope holes at web-flange intersections - Transverse stiffener terminations at beam flanges - Shear stud welds (hence the low Category F) - Weld terminations at splice plates
Design problem: Simple-span plate girder steel bridge, 40 m span, 2-lane carriageway 7.5 m, for state highway. E350 BR steel.
Step 1 — Loads per IRC 6: DL (steel girder + bracings + deck system) ≈ 60 kN/m per bridge SDL (wearing coat + kerb + parapet) ≈ 15 kN/m LL (Class 70R): max BM ≈ 10,500 kN·m at midspan (including impact factor 1.145)
Step 2 — Factored BM at midspan: M_u = 1.35 × (60 + 15) × 40²/8 × (loads distributed) + 1.50 × 10,500 (LL) For combined loads with 4 girders sharing: each girder takes ~1/4 of total. Per girder: M_u ≈ 8,000 kN·m factored.
Step 3 — Girder sizing: Try 2.0 m deep girder with 25 mm flange plates × 500 mm wide, 12 mm web × 1,950 mm deep. Moment of inertia: I_xx ≈ 1.45 × 10⁹ mm⁴ Section modulus: Z_x = I_xx / y = 1.45 × 10⁹ / 1,000 = 1.45 × 10⁶ mm³
Moment capacity: M_d = β_b × Z_p × f_y / γ_m0 For plastic section with β_b = 1 (need to verify section classification): M_d = 1 × 1.45 × 10⁶ × 1.1 (plastic shape factor) × 350 / 1.10 = 505 × 10⁶ N·mm = 505 kN·m per million mm³
If Z_p calculated = 1.6 × 10⁶ mm³: M_d = 505 kN·m × 1.6 = 808 kN·m at capacity.
Wait, this needs dimensional correction. Let me redo: M_d = Z_p × f_y / γ_m0 = 1.6 × 10⁶ mm³ × 350 N/mm² / 1.10 = 509 × 10⁶ N·mm = 509 kN·m
Hmm, 509 kN·m < 8,000 kN·m required. Need deeper/heavier girder.
Retry: 2.5 m deep girder, 40 mm flange plates × 700 mm wide, 16 mm web × 2,420 mm: Z_p ≈ 10 × 10⁶ mm³ M_d = 10 × 10⁶ × 350 / 1.10 = 3,182 kN·m per girder
With 4 girders sharing 8,000 × 4 = 32,000 kN·m total — each girder carries ~8,000 kN·m. Require M_d ≥ 8,000 per girder.
Further: 3.0 m deep girder, 50 mm flange × 800 mm, 20 mm web: Z_p ≈ 20 × 10⁶ mm³ M_d = 20 × 10⁶ × 350 / 1.10 = 6,364 kN·m — still short.
Scale to full section: 3.5 m deep, 60 mm flanges: Z_p ≈ 30 × 10⁶ mm³ M_d = 30 × 10⁶ × 350 / 1.10 = 9,546 kN·m ≥ 8,000 ✓
Approximate girder weight per metre: steel density × cross-section area = 78.5 × (2 × 60 × 800 + 20 × 3400) = 78.5 × (96,000 + 68,000) = 78.5 × 164,000 = 12.9 kN/m of girder = 1,290 kg/m. High but acceptable.
Note: This simplified example shows the iterative nature of steel girder design. In practice, engineers use software (STAAD, MIDAS Bridge) to efficiently optimize section depth vs flange/web thickness for minimum weight while satisfying all IRC 24 limit states.
1. Ignoring fatigue. The #1 cause of older steel bridge distress. Design for static strength + serviceability + fatigue simultaneously. Missing fatigue check has led to premature cracking in 20-30 year old Indian steel bridges.
2. Wrong material specification. E250 is cheap but inappropriate for bridge-scale spans. E350 BR or E450 CR are bridge-grade defaults. E350 D for cold regions. Don't default to ordinary building-grade steel.
3. Stiffener design for buckling. Slender webs need intermediate and bearing stiffeners per Clause 508. Missing bearing stiffeners at supports is a classic design error that causes web crippling.
4. Wrong welding procedure specification. Bridge welds must be full-penetration at critical flange-web connections per AWS D1.5 or IS 9595. Fillet welds alone are inadequate and fatigue-critical. Specify weld type explicitly in drawings.
5. Skipping the bolt-friction check. HSFG bolted connections rely on friction between plates (not bearing). Slip load = μ × N × clamping force, where μ is friction coefficient. Contact surface preparation (grit-blasted vs mill-scale) affects μ significantly. Specify surface prep in drawings.
6. Construction stage analysis missing. Steel bridges often erected in segments with temporary supports. Each stage has different stress distribution than final service. Construction-stage analysis is mandatory but often skipped on smaller projects.
IRC 24:2010 is the current code. Amendments (2012, 2018) clarified stiffener design, added provisions for self-compacting concrete deck connections, and expanded fatigue detail categories.
Indian steel bridge market reality: - Long-span crossings (>100 m) are dominated by steel — Mumbai Trans-Harbour Link, Pamban Railway Bridge replacement, and major river crossings - Mid-span bridges (20-60 m) mostly composite (IRC 22) or RCC (IRC 112) — steel only when specific advantage (fast erection, congested site) - Railway bridge renewal drives continued steel bridge activity across Indian Railways - Tier-1 fabrication: L&T Infotech, Tata BlueScope, Bridge & Roof Company, Braithwaite & Co, JSW Steel - Quality control at fabrication shops has improved dramatically in the last 15 years — NDT (UT, RT, MPT) is now standard on all NH bridge girders
For any steel bridge project: 1. Specify IS 2062 grade + quality class + welding code in drawings 2. Mandate fabrication-shop QA per AWS D1.5 3. Require NDT on all critical welds — UT and MT on butt welds, VT on fillets 4. Inspect surface preparation for HSFG bolts and corrosion coating 5. Plan for fatigue testing on critical details (wheel load test on prototype)
Upcoming revision expected 2027 to modernize fatigue categories, add weathering steel (Cor-Ten equivalent), and explicitly cover ultra-high-strength steels (E550-E650).
| Parameter | IS Value | International | Source |
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