IRC SP 65:2005 is the Indian Standard (IRC) for guidelines for design and construction of segmental bridges. This code is essential for engineers involved in the design and construction of segmental bridges, a common and efficient construction method for medium to long-span bridges. It details the principles of segment design, focusing on precast concrete units that are assembled and joined together, often using post-tensioning. The guidelines cover critical aspects such as segment geometry, reinforcement detailing, joint design, and the complex process of erection and stressing. Adherence to these guidelines is crucial for ensuring the structural stability, durability, and constructability of segmental bridges, leading to safer and more cost-effective infrastructure projects.
This IRC code provides comprehensive guidelines for the design and construction of prestressed concrete segmental bridges. It covers aspects from material selection and fabrication of segments to erection and post-tensioning, ensuring structural integrity and long-term performance. The code is intended for engineers involved in the planning, design, and execution of such bridges.
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Subject | Prestressed-concrete segmental bridge design/construction | Scope |
| Methods | Balanced cantilever / span-by-span / incremental launch | Construction |
| Prestress | Cantilever + continuity tendons; staged stressing | Design |
| Segment joints | Match-cast epoxy / wet joints | Detail |
| Construction stages | Each erection stage analysed | Design |
| Read with | IRC 18 / IRC 112 (PSC) / IRC 6 | Cross-ref |
IRC SP 65 (2005) provides Guidelines for Design and Construction of Segmental Bridges — the IRC's specification for precast / cast-in-place segmental box-girder bridges. Segmental construction has revolutionised long-span bridge construction in India, enabling spans of 60-200 m with minimal in-situ work + faster construction.
Use IRC SP 65 when you are: - Designing long-span concrete box-girder bridges (50-200 m spans) - Specifying precast segmental construction for bridge superstructure - Doing DPR for major river / flyover bridges with segmental design - Evaluating segmental vs cast-in-place vs steel alternatives - Specifying balanced cantilever construction (precast or in-situ) - Working on NHAI 4/6-lane projects with major water crossings - Designing urban flyovers with segmental construction for traffic-management benefits
What IRC SP 65 covers: - Segmental design concept + classification - Precast vs in-situ segment manufacture - Concrete + reinforcement specifications - Pre-stressing systems (internal + external + post-tensioned) - Erection methodology (cantilever vs span-by-span) - Joint design + segments connection - Geometric + construction tolerances - Quality assurance + control - Construction monitoring
Segmental bridge types: 1. Precast segmental (cantilever): factory-cast segments, erected by launching girder or crane 2. Cast-in-situ segmental (cantilever): segments cast in place using travellers 3. Span-by-span construction: entire span erected on temporary supports, then post-tensioned 4. Incremental launching: entire deck launched along supports 5. Free cantilever: segments cantilevered from pier without temporary support
Typical applications: - Major river bridges (Ganga, Brahmaputra, Krishna, etc.) - Urban flyovers in dense traffic areas - Long-span elevated metro - Sea-bridges (Bandra-Worli, Mumbai Trans-Harbour) - Expressway viaducts
Design philosophy: - Box-girder cross-section optimised for moment + shear capacity - Pre-stressing tendons placed for maximum efficiency - Joint locations engineered to handle stress transfer - Movement accommodation (creep, shrinkage, thermal, traffic) per IRC:SP-77:2008
Segment manufacture: - Precast (typical box segment): - Length: 2-5 m - Weight: 50-200 tonnes - Surface quality: high (match-cast) - Casting cycle: 1-2 segments per casting bed per shift - Cast-in-situ: - Cast in place using moving formwork (traveller) - Segment length: 3-5 m - Construction cycle: 5-10 days per segment
Match-casting (precast): - Each new segment cast against previous; match surface - Ensures geometric continuity - Joint surface uses lubricant + match-mark for assembly - Precision required: ± 5 mm at joint plane
Pre-stressing systems: - Internal post-tensioning: ducts cast into concrete; tendons inserted after curing - External post-tensioning: tendons outside concrete (often in deviation troughs) - Bar pre-stressing: rare; mostly for short-span - Tendon types: 7-wire low-relaxation strands per IS 14268
Joint design + connection: - Dry joints (no epoxy): rare for road bridges; used in walkways - Epoxy joints (most common): thin epoxy adhesive between match-cast surfaces - Shear-key + epoxy: mechanical interlock + adhesive - Wet joints: in-situ concrete fill at segment interfaces
Erection methodology: 1. Launching girder erection: crane-mounted launching girder lifts + positions segments; common for medium spans 2. Trapeze erection: cantilever erection beam from pier 3. Float-in erection: segments transported by water; lifted by crane on barge 4. Span-by-span: erection on temporary supports; pre-stressed after assembly 5. Free cantilever: progressive cantilever from each pier; closing at mid-span
Concrete grade: - Cast-in-place segments: M40-M45 minimum - Precast segments: M40-M55 (higher strength enables thinner sections) - Joint material (epoxy): per supplier spec; bond strength ≥ 4 MPa
Pre-stressing: - Tendon material: 7-wire strand per IS 14268; UTS typically 1860 MPa - Stress at jacking: ≤ 75 % of UTS = ~1395 MPa - Stress after losses: ≤ 70 % UTS = ~1300 MPa - Anchorage zone: per IS 1343 + IRC SP 65; specific reinforcement detailing
Reinforcement: - Conventional steel: Fe 500 typical - Anchorage zone: additional ties + stirrups - Cover requirements per IRC:112:2020: typically 50 mm to outer faces
Segment dimensions (typical box-girder): - Depth: span/15 to span/20 (for medium spans) - Width: matches bridge width (typically 12-25 m for 4-6 lane) - Top slab thickness: 200-300 mm - Bottom slab thickness: 200-400 mm (thicker at supports) - Web thickness: 250-500 mm
Casting + curing (precast): - Cement content: 380-420 kg/m³ - W/C ratio: 0.35-0.42 - Slump: 100-150 mm (workable for placement around tendon ducts) - Curing: 28-day strength critical; heat-treated for early strength (50-60 % at 24 hrs) - Steam curing: 50-65 °C for 12-18 hours (accelerated) - Demoulding strength: 28 MPa minimum
Joint construction: - Match-cast precision: ± 5 mm - Surface preparation: clean, dry, free of release agent - Epoxy application: full coverage + adequate thickness (1-2 mm) - Curing pressure: maintained for full epoxy cure (4-12 hours) - Acceptance: visual + non-destructive
Erection tolerances: - Segment alignment: ± 5 mm vertical, ± 10 mm horizontal - Joint gap: ± 2 mm of design - Deck level: ± 10 mm of design - Camber: ± 5 mm of design (cantilever construction)
Pre-stressing application: - Sequential jacking per design - Verify tendon elongation at each step (± 5 % of theoretical) - Force measurement via load cells + pressure gauges - Post-stressing inspection of anchorage zones
Acceptance criteria: - Segment dimensions + alignment within tolerance - 28-day concrete strength meets design - Pre-stressing force verified - Joint bond + integrity verified - Camber + final geometry as designed - Visual inspection: no major cracks; minor cracks documented
Service life + maintenance: - Design life: 75-100 years - Service life depending on environment + maintenance - Routine inspection: annual visual + 5-year detailed - Major rehabilitation: at 50+ years typical
1. Match-cast precision lost. Segments don't fit; rework + delay. Strict precision control in casting bed. 2. Epoxy joint quality poor. Bond inadequate; cracks open at joint over time. Procedure + supplier qualification. 3. Pre-stressing loss greater than design. Friction + anchorage losses; effective force below design. Verify per design + lab measurements. 4. Tendon corrosion. Inadequate grouting in ducts; corrosion + tendon failure. Proper grouting per IS 9067; inspection. 5. Anchorage zone reinforcement insufficient. Pre-stressing causes localised damage; future cracking. Detail per IS 1343 + IRC SP 65. 6. Camber off design. Cantilever segments deflect more than expected; profile wrong; rework. Conservative camber + monitoring. 7. Erection equipment failure. Launching girder fails; safety + delay. Robust design + inspections. 8. Joint location at high-stress. Joints in zones of high moment / shear; structural concern. Joint locations engineered. 9. Concrete strength low. 28-day strength below design; pre-stressing risky. Strict mix design + acceptance testing. 10. No NDT on segments. Reliance on visual; sub-surface defects missed. UT / radiography on critical segments. 11. As-built deviates from design. Construction deviations not documented; future maintenance / forensic uncertain. Comprehensive as-built records. 12. Construction monitoring inadequate. Deflections + stresses not measured; behavior unknown. Strain gauges + survey monitoring during construction. 13. Weather sensitivity. Outdoor casting in monsoon; quality compromised. Schedule indoor casting where possible. 14. Coordination with substructure. Segmental erection requires precise substructure alignment; substructure errors cause cascading issues. Tight coordination. 15. No load test post-erection. Design intent not verified; uncertainty. Load test per IRC:SP-51:2015 for major bridges. 16. Joint sealant degradation. Outer sealant not maintained; moisture entry; tendon corrosion. Maintenance contract. 17. Maintenance access difficult. Box-girder interior cramped; inspection difficult. Access provision during design.
Segmental bridge project — IRC SP 65 touchpoints:
1. DPR + design: - Span configuration - Segmental construction selected for technical / cost reasons - Concrete + pre-stressing specifications - Erection method (cantilever / span-by-span / launching) - Geometric design + camber
2. Manufacturing setup: - Casting bed design + construction - Mould fabrication - QC laboratory - Trial segments + match-casting verification - Production cycle established
3. Mass production (precast): - Concrete batching + placement - Reinforcement + pre-stressing duct placement - Match-casting per cycle - Curing (heat-treated typically) - QC testing - Storage + handling
4. Erection: - Substructure construction - Erection equipment installation - Sequential segment erection - Joint placement (epoxy + bonding) - Pre-stressing per sequence - Geometric verification - Survey + alignment
5. Closure + post-stressing: - Closing segment (cantilever method) - Additional pre-stressing - Final geometric verification - Removal of erection equipment
6. Finishing: - Wearing coat per IRC:7:2017 - Bearings + joints per IRC:19:2005 - Drainage + lighting - Approach works
7. Quality control + acceptance: - Segment QC per IRC SP 57 - Pre-stressing force verification - Joint integrity - Geometric tolerance verification - 28-day concrete strength - Load test (if specified per IRC:SP-51:2015)
8. Operations + maintenance: - Annual visual inspection - 5-year detailed inspection per IRC:SP-71:2018 - Bearing + joint replacement cycle - Long-term: 75-100 year service life
IRC SP 65 is the specialised reference for segmental construction — invoked on major Indian bridges (Bandra-Worli, Mumbai Trans-Harbour, Krishna Bridge, Vidyasagar Setu, many others). The 2005 specification remains current + applied on every modern major bridge project.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Minimum Concrete Grade | |||
| Allowable Concrete Compression Stress (Service) | |||
| Allowable Steel Stress (Service) | |||
| Minimum Segment Length | |||
| Maximum Aggregate Size |