IRC Code: IRC:SP:65-2018 – Guidelines for Design and Construction of Segmental Bridges

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The Indian Roads Congress (IRC) plays a crucial role in setting the standards for road and bridge construction in India. One such significant publication is IRC:SP:65-2018, which provides Guidelines for the Design and Construction of Segmental Bridges. This code is a revision of the previous edition (published in 2006) and aligns with modern bridge design approaches, particularly with IRC:112.

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Segmental bridges are widely used due to their efficiency in construction, cost-effectiveness, and ability to span large distances with minimal disruption to traffic. The updated IRC:SP:65-2018 integrates advanced engineering principles, international best practices, and innovations in prestressed concrete bridge construction.

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Scope of IRC:SP:65-2018

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Segmental bridge construction involves assembling multiple precast or cast-in-situ segments, either by cantilever construction, span-by-span erection, or spliced girder systems. This methodology ensures faster bridge construction, higher quality control, and reduced dependency on scaffolding.

The scope of IRC:SP:65-2018 includes:

• Design considerations for epoxy-jointed precast segmental superstructures
• Guidelines for cantilever construction (precast or cast-in-situ)
• Spliced girder systems with match-cast joints
• Requirements for precast and cast-in-situ prestressed concrete segmental superstructures

These guidelines apply to highway bridges, urban flyovers, and metro rail structures where segmental construction is advantageous.

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Design Considerations

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Structural Differences and Joint Considerations

The primary difference between segmental and non-segmental bridges lies in the presence of joints. The design of segmental bridges follows IRC:112, with additional provisions to address:

• Joint efficiency and load transfer
• Allowable stresses in concrete and steel
• Crack width limitations
• Shear and torsion considerations

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Load Combinations and Safety Factors

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The design must consider Ultimate Limit State (ULS) and Serviceability Limit State (SLS) criteria. The applicable loads are derived from IRC:6. Special factors are included for precast segmental bridges with bonded and unbonded tendons.

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Construction Requirements

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Precasting and Assembly

Segmental bridges require precise precasting techniques. The recommended methods include:

• Long-line method: Segments cast sequentially and aligned
• Short-bench method: Individual segments are cast and stored separately
• Match casting: Ensuring perfect joint fitment between segments

Tolerances for precast segments are strictly defined to maintain structural integrity and geometric accuracy.

Epoxy Jointing and Shear Keys

For precast segmental bridges, epoxy jointing ensures monolithic behavior. Shear keys enhance load transfer and prevent slip at joints.

External Prestressing and Deviators

External prestressing is a common technique in segmental construction. The IRC:SP:65-2018 prescribes:

• Replaceable anchorage systems
• Grouting techniques for protection against corrosion
• Deviator blocks to guide external tendons and minimize vibrations

Waterproofing and Durability

Segmental bridges require high durability standards. Waterproofing membranes, corrosion protection, and high-strength cementitious grout are mandatory for longevity.

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Advantages of Segmental Bridge Construction

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1. Faster Construction

Segmental bridges enable rapid assembly, reducing construction time significantly.

2. Cost Efficiency

Reduction in formwork, scaffolding, and labor costs makes segmental bridges economically viable.

3. Minimal Traffic Disruptions

Precasting allows off-site fabrication, minimizing on-site congestion and traffic disturbances.

4. High Structural Performance

Segmental bridges exhibit superior load-carrying capacity, seismic resilience, and fatigue resistance.

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Conclusion

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The IRC:SP:65-2018 serves as a comprehensive guide for engineers, designers, and construction professionals involved in segmental bridge projects. By incorporating modern methodologies and international best practices, this IRC Code ensures the safe, durable, and cost-effective construction of segmental bridges in India.

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