Post tensioning: Bridges |

June 14, 2023

Post-tensioning is a technique used extensively in modern bridge construction. It involves applying compression after the concrete has set, enhancing the strength and durability of the structure. This method has been instrumental in creating large, efficient, and sustainable structures, such as post tensioning bridges.

Read more: We explain how much post-tensioning costs and what modular construction is.

How is Post-Tensioning Used in Bridges?

The process begins by placing steel tendons — high-strength steel cables — within ducts that run through the concrete elements, such as post tensioning beams. Once the concrete hardens, hydraulic jacks tension these tendons. The tendons are then anchored, and the ducts are grouted, providing additional protection to the steel. The resulting tension counteracts loads applied to the bridge, significantly reducing the stress on the structure.

Key steps in post-tensioning include:

  1. Placing steel tendons in the concrete elements.
  2. Tensioning the steel tendons after the concrete has set.
  3. Anchoring the tendons and filling the ducts with grout.

What are the Advantages of Post-Tensioning in Bridges?

Post-tensioning confers numerous advantages, making it a preferred technique in modern bridge construction.

  1. Enhanced Strength: It increases the bridge's load-bearing capacity, allowing it to withstand heavy traffic and adverse weather conditions.
  2. Durability: It provides greater resistance to cracking and damage, thereby extending the bridge's lifespan.
  3. Design Freedom: It allows construction of slender, longer span structures with unusual geometry, enabling architects to push the boundaries of design.
  4. Economical: It reduces the amount of materials needed, lowering costs and making construction more efficient.
  5. Sustainability: Less materials usage also translates to a smaller carbon footprint, making post-tensioning a more sustainable choice.

Read more: Learn more about modular house construction and how it compares to traditional construction.

A big bridge constructed over water in Lisbon

Examples of Bridges with Post-Tensioning

Numerous iconic bridges around the world have employed post-tensioning, showcasing its advantages.

The Millau Viaduct, France

This cable-stayed bridge is one of the tallest in the world, with post-tensioning employed in its construction to achieve an incredible span length and height.

The Sunshine Skyway Bridge, USA

Known for its unique design, post-tensioning was used to ensure its longevity and strength, standing against Florida's hurricanes.

The Confederation Bridge, Canada

This 8-mile-long bridge, connecting Prince Edward Island with mainland New Brunswick, is the world's longest bridge over ice-covered waters. Post-tensioning was utilised to ensure its endurance against harsh climatic conditions.

The Bill Emerson Memorial Bridge, USA

The bridge's main span features post-tensioned concrete girders, illustrating the technique's ability to support large, heavy structures over significant distances.

The Bandra-Worli Sea Link, India

This cable-stayed bridge in Mumbai features post-tensioned concrete-steel viaducts on either side of the cable-stayed spans. This design showcases how post-tensioning can coexist with other construction techniques for efficient outcomes.

These structures underline how post-tensioning can deliver robust and reliable bridges, capable of withstanding various environmental conditions and meeting unique design needs.

The bandra-worli sea link in India

Future of Post-Tensioning in Bridges

Post-tensioning continues to evolve with the advancement of material sciences and engineering techniques. Innovations in high-strength materials and design software promise to enhance the advantages of post-tensioning, opening up new possibilities for bridge design and construction.

For instance, advancements in corrosion-resistant tendons or improved grouting materials can further enhance the durability of post tensioning bridges. Similarly, digital tools can streamline the design process, allowing engineers to optimise the use of post-tensioning in varied and complex structures.

Post-tensioning and sustainability

Post-tensioning has become a cornerstone in modern bridge construction. By optimising material usage, providing increased durability, and enabling innovative design, it brings substantial benefits. Whether in post tensioning bridges or post tensioning beams, the application of this technique ensures structures that stand the test of time. 

Read more: We discuss the advantages of modular construction and its environmental benefits.

Frequently asked questions

What is the purpose of post tensioning?

Post-tensioning strengthens concrete by applying tension after it cures, improving its durability and load-bearing capacity. Steel cables or bars are used to introduce tension, enhancing crack resistance and overall structural strength. It works well for both bridges and buildings

Is post-tensioning the best way to create durable bridges?

Post-tensioning is a top choice for creating durable bridges due to its reinforcement capabilities, enhanced load-bearing capacity, and superior lifespan compared to traditional methods. However, project requirements and design considerations should be taken into account for its suitability.

Are there other techniques available for building bridges?

Some other techniques available for building bridges that offer comparable durability to post-tensioning include pre-stressed concrete construction, steel truss bridges, and cable-stayed bridges.

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