IRC Code 115:2018 - Guidelines for Design of Integral Bridges

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Integral bridges are gaining popularity due to their ability to provide enhanced durability, reduced maintenance costs, and improved structural performance. The Indian Roads Congress (IRC) introduced IRC:SP:115-2018 to offer comprehensive guidelines on the design, detailing, and construction of integral bridges in India.

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Importance of Integral Bridges

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Traditional bridges use expansion joints and bearings, which require frequent maintenance and can lead to structural deterioration. Integral bridges eliminate these weak points by making the deck and substructure monolithic. This results in:

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• Lower maintenance costs due to the absence of expansion joints and bearings.
• Better seismic performance as the bridge acts as a single, continuous unit.
• Improved ride quality for commuters.
• Enhanced durability with reduced water ingress and corrosion.

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Key Highlights of IRC Code 115:2018

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1. Understanding Integral Bridges

• Fully Integral Bridges: No expansion joints or bearings, the deck and abutments act as a single unit.
• Semi-Integral Bridges: No expansion joints at abutments, but bearings are provided at piers.
• Framed-Type Bridges: Deck is monolithic at piers but has bearings and expansion joints at abutments.

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2. Design Considerations

• Length Limitations: Integral bridges up to 60m are preferred in many countries like the UK; however, longer spans can be designed using advanced engineering techniques.
• Soil-Structure Interaction: The design must consider the movement of the structure with surrounding soil.
• Temperature Effects: Bridges expand and contract with temperature variations, and integral bridges must accommodate these movements effectively.

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3. Structural Design and Load Considerations

• Superstructure Design: Use of reinforced concrete (RC), prestressed concrete (PSC), or composite materials.
• Substructure and Foundation:
  • Pile foundations are common to allow flexibility.
  • Spread footings may be used where soil conditions permit.
• Load Combinations:
  • Thermal Movements: Bridges must withstand expansion and contraction forces.
  • Seismic Loads: Integral bridges offer better seismic resistance due to monolithic action.
  • Earth Pressure: Consideration of active and passive earth pressures on abutments.

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4. Construction and Maintenance Aspects

• Construction Sequence:
  • Abutments are built first, followed by deck placement.
  • Proper curing is essential to prevent early-age cracking.
• Backfill and Drainage Considerations:
  • Well-compacted granular backfill minimizes settlements.
  • Adequate drainage systems prevent water accumulation behind abutments.
• Regular Inspection and Maintenance:
  • Checking for cracks at abutment-deck connections.
  • Ensuring proper drainage to avoid waterlogging issues.

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Challenges and Solutions in Implementing Integral Bridges

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• Design Complexity: Requires advanced structural analysis techniques.
• Limited Span Length: Currently preferred for short- to medium-span bridges.
• Soil Compatibility: Integral bridges perform better on stable, non-liquefiable soils.

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Conclusion

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The IRC:SP:115-2018 - Guidelines for Design of Integral Bridges provides engineers with essential best practices to design and construct durable, low-maintenance, and structurally resilient bridges. By adopting integral bridge concepts, India can enhance its infrastructure with cost-effective, long-lasting, and high-performance bridges.

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