Construction Methods for Prestressed Concrete Bridge Decks and the Role of Formtravellers

The construction of prestressed reinforced concrete bridge decks and viaducts can generally be divided into two large families:

• In situ concrete bridges, where the deck is cast on site.
  
• Prefabricated bridges, where large structural elements are manufactured in a factory environment and later assembled on site.
  

Within the in situ family, several types of equipment are commonly used for the construction of prestressed concrete decks. Today, the main ones are:

• Ground-supported falsework
  
• Pier-supported falsework
  
• Incremental Launching systems
  

Among these, pier-supported falsework plays a key role when ground access is difficult (rivers, valleys, railways) or when ground-supported systems would be uneconomical or unsafe.

Pier-supported falsework: Formtravellers and Movable Scaffolding Systems

The most widely used pier-supported systems are:

• Formtravellers
  
• Movable Scaffolding Systems
  

These two families serve different structural solutions:

• Formtravellers are used to construct bridge and viaduct decks by the cantilever method. The deck is built in successive segments projecting from a pier, usually in symmetric pairs, one on each side of the pier axis.
  
• Movable Scaffolding Systems are used for bridge and viaduct decks designed as concrete beams supported on columns, where spans are cast in situ with support on the piers.
  

In both cases, the deck is constructed in sections:

• With Formtravellers, the deck is built in segments, typically up to 5 m long. In some special cases, segment length can be increased up to 10 m.
  
• With Formtraveller Systems, the deck is also constructed in sections, but typically one full span at a time. Concreting joints are usually placed at approximately 1/5 of the span length, where the bending moment is close to zero.
  
  

Types of Formtraveller 

Formtraveller have evolved into several specialised configurations to respond to different types of structures:

1. Overhead Formtraveller
   
   • The main structure is located above the deck.
     
   • The formwork is suspended from this upper structure.
     
2. Underslung Formtraveller
   
   • The main structure is located under the deck.
     
   • The formwork rests on the lower structure.
     
     
3. Arch Formtraveller
   
   • A specialised solution developed to allow the casting of concrete arch segments.
     
     
4. Wing Formtraveller
   
   • Typically used to cast deck wings, either for composite decks or for fully concrete decks.
     
     

Advantages of Formtraveller 

Formtraveller offer several important advantages for the construction of bridges and viaducts:

• They allow large spans to be cast in situ by the cantilever method, segment by segment.
  
• Segments are usually cast in symmetric pairs from each column, which balances cantilever moments and is structurally efficient.
  
• They are environmentally friendly, as their useful life can exceed 50 years, allowing reuse on many projects.
  
• Their energy consumption during operation is generally low compared to alternative heavy construction methods.
  
  

Overhead vs Underslung Formtraveller: how to choose?

• For the same segment length and segment weight, the Overhead Formtraveller System is usually lighter and cheaper than the Underslung solution.
  
  

This makes the overhead configuration particularly attractive.

STRUKTURAS
WE MAKE IT SIMPLE!