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Formwork, Operations and Logistics in Formtraveller

Formwork, Operations and Logistics in Formtraveller

Formwork, Operations and Logistics in Formtraveller 

The efficiency of a Formtraveller depends heavily on how the formwork is designed and handled, and how site operations and logistics are planned. This includes panel dimensions, formwork surfaces, internal formwork launching, crew size, launching speed and workshop pre-assembly.

 

Internal and external formwork: configuration and handling

In typical applications, the external and internal formwork panels have a length of about 5.8 m, assuming a maximum segment length of 5 m in the concrete deck.

Internal and external panels are connected using threaded ties, such as Dywidag bars, passing through the deck webs. This creates a closed, stable formwork box that can carry fresh concrete and construction loads.

The internal formwork in Formtravellers is usually launched manually from one segment to the next:

  • Chain tackles are commonly used to move the internal formwork along rails.
  • Hydraulic cylinders can also be adopted, but the standard solution in many projects remains manual.
  • The rails on which the internal formwork rests are launched together with the main structure of the Formtraveller.

As mentioned earlier, the position of internal diaphragms must allow the internal formwork to pass. If diaphragms are too close to the front of the segment, the internal formwork may need to be dismantled behind the diaphragm.

 

Formwork surfaces and materials

The most common formwork surface used in Formtraveller Systems is:

  • Phenolic plywood, usually 21 mm thick.

Steel formwork surfaces are technically possible but rarely preferred:

  • Rebuilding steel formwork for future projects is costly.
  • For typical segment lengths and project sizes, plywood offers a better economic balance.

The usual arrangement is:

  • Plywood sheets are screwed to timber sections.
  • Timber sections are bolted to the steel ribs of the formwork structure.
  • Parts of the internal and external web formwork are often made using wooden beams.

If the number of segments is very high, the phenolic plywood can be replaced during the life of the Formtraveller, while the underlying steel structure remains reusable.

 

Handling reinforcement: limits and special solutions

As a rule:

  • Overhead Formtraveller do not normally allow the transport of pre-assembled reinforcement cages on the system itself.

However, in some specific projects where:

  • The deck webs are vertical or nearly vertical, and
  • Pre-assembled web rebar panels are desired,

it may be possible to develop special transport rails integrated into the Formtraveller. In such cases:

  • A crane installs the pre-assembled web reinforcement panel.
  • The load is then transferred from the crane to the special rails of the Formtraveller.

These are project-specific solutions, not the standard configuration.

 

Crew size, launching speed and construction cycle

To operate a Formtraveller– including:

  • Opening the formwork
  • Launching from one segment to the next
  • Closing the formwork
  • Introducing camber
  • Preparing the formwork for reinforcement
  • Concreting the segment

– a dedicated crew is required. 

The exact crew size depends on the segment weight, deck width and the target construction cycle, but in general:

  • A team of 8 to 10 people per pair of Formtravellers is typical.

Regarding relocation speed:

  • The normal launching speed of a Formtraveller is around 10 m per hour.
  • Increasing the launching speed does not make practical sense, since the maximum segment length is only about 5 m. The marginal time savings are minimal, and the risks associated with higher movement speeds increase.

The typical construction cycle for a pair of segments using Formtravellers is approximately:

  • 1 week per pair of segments,
     assuming standard times for reinforcement assembly, prestressing operations, concrete curing, and formwork operations.

Workshop pre-assembly, transport and on-site planning

During the original manufacture of a Formtraveller System:

  • The steel structure is usually partially pre-assembled in the workshop.
  • All components are marked with references, indicating their position in the final assembly.

For transport:

  • Parts are designed to fit in 40-foot containers or on TIR truck platforms.

On site, careful planning of assembly and dismantling is essential:

  • Correct definition of lifting points for sub-assemblies.
  • Ensuring that the centre of gravity of each assembly stage remains within safe limits.
  • Guaranteeing suitable access for cranes and transport equipment.

Accurate weights of all parts must be known:

  • Typically derived from 3D models or detailed 2D drawings.
  • If there is any uncertainty, scales can be used to confirm the component weights.

Design Criteria Document: selecting the right Formtraveller 

To evaluate whether a given Formtraveller is suitable for a specific bridge deck, it is essential to prepare a Design Criteria Document. This document must clearly define at least:

  • Loads from the concrete segments and launching situation
  • Safety factors
  • Wind speeds:
    • During launching
    • During concreting
    • Under storm conditions
  • Materials and steel grades
  • Maximum span
  • Live loads and other construction loads

The cost and site performance of a Formtraveller depend strongly on these definitions. A well-prepared Design Criteria Document is therefore the key technical basis for:

  • Deciding whether an existing system can be reused or adapted, or
  • Designing a new system optimised for the specific project.

In most successful cantilever projects, the Formtraveller is not an afterthought but an integral part of the initial design strategy for the bridge.

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