Short Answer:

Segmental construction in bridges is a method where the bridge is built in smaller parts called segments instead of one complete structure at once. These segments can be precast in a factory or cast-in-place on-site and then joined together using methods like post-tensioning.

This technique is mainly used in long-span bridges, especially where working space is limited or access is difficult. Segmental construction is fast, economical, and offers better quality control, making it ideal for complex bridge projects over rivers, roads, or urban areas.

Detailed Explanation:

Segmental construction in bridges

Segmental construction is a modern and efficient method used in bridge engineering where the entire structure is built by assembling smaller concrete sections called segments. Instead of casting the whole bridge deck or girder at once, it is divided into manageable units which are constructed and connected sequentially. This approach is useful for building long-span bridges, especially over obstacles like rivers, highways, or railway lines, where using traditional full-length formwork is difficult or not practical.

The segments can be precast in factories or cast-in-situ at the site. They are usually joined together using post-tensioning, where steel tendons are threaded through ducts in the segments and then tightened to hold the sections firmly together. The segments are placed either by cranes, launching girders, or balanced cantilever techniques depending on site conditions and bridge type.

Features of Segmental Construction

1. Modular Construction
   • The bridge is built in parts, allowing flexibility and staged construction.
   • Each segment typically ranges from 2 to 5 meters in length.
2. Quality Control
   • Precast segments are manufactured in controlled environments, ensuring better concrete quality and finishing.
   • Less affected by weather compared to cast-in-place methods.
3. Speed and Efficiency
   • Segments can be produced and installed simultaneously, reducing total construction time.
   • Suitable for fast-track projects and high-traffic urban areas.
4. Post-Tensioning
   • Steel cables are used to apply compressive force across the segments, keeping them tightly joined.
   • Increases strength and reduces cracking under load.

Applications of Segmental Bridge Construction

1. Long-Span Bridges
   • Ideal for spans over rivers, valleys, or highways where scaffolding or ground support is hard to install.
   • Reduces the need for falsework or temporary supports.
2. Urban and Elevated Roads
   • Used for flyovers and metro rail viaducts where space is limited.
   • Causes less traffic disruption during construction.
3. Balanced Cantilever Bridges
   • Used for bridges where segments are added on both sides of a pier in a balanced way.
   • Maintains stability without external support.
4. Cable-Stayed and Box Girder Bridges
   • Segmental construction is compatible with complex bridge types that need high torsional stiffness.

Advantages of Segmental Construction

• Faster construction with minimal traffic disturbance
• Suitable for inaccessible or sensitive locations
• High precision and uniformity in segment shapes
• Reduced labor and scaffold requirements
• Easier quality checking before installation

Challenges

• Requires accurate alignment and planning
• Specialized equipment like launching girders may be needed
• Skilled workforce is required for segment handling and post-tensioning
• Joints between segments need proper sealing to prevent leakage and corrosion

Codes like IRC SP 65 and IRC 6 provide guidelines on the design, handling, and erection of segmental bridges in India.

Conclusion:

Segmental construction in bridges is a smart technique where bridges are built in small, manageable parts that are assembled together. It improves construction speed, quality, and safety, especially for long spans and complex locations. With proper planning and execution, segmental bridges offer strong, durable, and visually appealing structures.