IRC Code: IRC:SP:66-2016 – Guidelines for Design of Continuous Bridges

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The Indian Roads Congress (IRC) is the premier body responsible for setting the technical standards for road and bridge construction in India. One of its important publications is IRC:SP:66-2016, which provides Guidelines for the Design of Continuous Bridges. This code serves as a crucial reference for engineers, ensuring the efficient and safe design of continuous bridges using modern engineering techniques.

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Continuous bridges, unlike simply supported structures, offer enhanced structural efficiency, reduced maintenance needs, and better durability. IRC:SP:66-2016 aligns Indian bridge design with international best practices, optimizing structural performance and cost-effectiveness.

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Scope of IRC:SP:66-2016

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This IRC Code covers the design aspects of continuous bridges, including reinforced concrete (RC), prestressed concrete (PSC), and composite structures. Key areas of focus include:

• Load distribution and structural behavior
• Continuity effects, including thermal, creep, and shrinkage considerations
• Limit State Design (LSD) approach as per IRC:112
• Guidelines for seismic design and expansion joints
• Detailing requirements for reinforcement, prestressing, and deck systems

The guidelines apply to national highways, state highways, metro rail systems, and urban bridges, ensuring optimized performance and long-term sustainability.

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Design Considerations

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Structural Advantages of Continuous Bridges

Continuous bridges are designed to eliminate intermediate joints, reducing structural vulnerabilities. Some key advantages include:

• Better load distribution: Uniform stress distribution improves longevity.
• Reduced maintenance: Fewer joints mean lower wear and tear.
• Increased structural integrity: Enhanced seismic resilience and vibration control.

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Load Combinations and Safety Factors

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The design philosophy in IRC:SP:66-2016 follows the Limit State Method (LSM), ensuring both Ultimate Limit State (ULS) and Serviceability Limit State (SLS) criteria are met. Loads and safety factors are as per IRC:6-2017.

The major design loads considered include:

• Dead loads and superimposed dead loads
• Traffic loads (as per IRC:6)
• Wind and seismic forces
• Temperature, shrinkage, and creep effects

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Continuity Effects and Expansion Considerations

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Continuous bridges require careful evaluation of:

• Creep and shrinkage effects: Critical for prestressed bridges.
• Temperature gradients: Addressed using expansion joints and flexible bearings.
• Seismic effects: Special detailing to ensure ductility and resilience.

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Construction Guidelines

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Material Specifications

• Minimum concrete grades: As per IRC:112-2011.
• Durability criteria: Adequate cover, corrosion protection, and waterproofing.
• Prestressing methods: Internal and external prestressing guidelines.

Bearings and Expansion Joints

Proper selection of bearings and expansion joints ensures long-term performance. IRC:SP:66-2016 provides detailed recommendations for:

• Elastomeric bearings
• Pot bearings
• Sliding and rocker bearings

Reinforcement and Prestressing Details

• Proper anchorage zones to prevent stress concentrations.
• Duct layouts optimized for prestressing efficiency.
• Shear and torsion reinforcements at critical sections.

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Advantages of Continuous Bridge Design

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1. Cost-Effective Construction

Continuous bridges reduce material consumption, making them economical compared to simply supported spans.

2. Lower Maintenance Costs

With fewer expansion joints and bearings, maintenance is minimized.

3. Improved Aesthetics

Smoother bridge profiles enhance visual appeal and aerodynamic efficiency.

4. Enhanced Seismic Performance

Continuous decks provide better energy dissipation during earthquakes.

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Conclusion

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The IRC:SP:66-2016 is an essential guideline for designing continuous bridges, ensuring structural efficiency, longevity, and cost-effectiveness. By incorporating modern design principles and international best practices, this IRC Code enhances the safety and reliability of bridge structures across India.

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