The Strukturas Formtraveller system is a modern solution for cast in-place, prestressed concrete bridge and viaduct decks. As a type of pier-supported falsework, it enables bridge decks to be built without relying on ground-supported scaffolding. During construction, the Formtraveller carries the fresh concrete, reinforcement, workers, and formwork, safely transferring these loads into the completed portion of the structure.
As prestressed concrete technology advanced, the need arose for adaptable equipment capable of following the sophisticated geometry of slender, curved decks while still allowing long spans to be built efficiently. Over several decades Strukturas has refined its Formtraveller solutions, creating systems that adapt to many deck cross-sections, span lengths, longitudinal slopes, and plan radii.
We will explain all the types of form travelers and their differences, advantages here, for your deeper understanding, but you do not need to become an expert in this, because our team would choose the best solution for your individual needs.
Balanced Cantilever Construction with Formtravellers
In balanced cantilever construction, a pair of Formtravellers is mounted on top of a pier. Segments are cast outward from both sides in a symmetrical pattern to maintain balance. Each segment is cast in place, reaches the required strength, is prestressed, and becomes part of the permanent structure. After completion of a segment, the Formtraveller is released and launched to the next position.
Typical segment lengths are around five meters, though in special cases they may reach approximately ten meters. This construction method is ideal for viaducts over deep valleys, rivers, or busy infrastructure where ground-supported falsework is not feasible. The resulting prestressed concrete deck is structurally efficient, slender, and durable.
Form-traveller Systems for Span-by-Span Decks
Formtraveller Systems are used when the deck acts as a concrete beam supported directly on columns. Instead of building segments from the pier, each span is cast in one operation. Construction joints are placed near points of zero bending moment – often at roughly one-fifth of the span length – allowing the deck to behave as a continuous structure while keeping the sequence simple and repetitive.
Overhead Formtraveller
In an overhead Formtraveller the main steel structure sits above the deck, with the formwork suspended from it. This configuration is particularly effective when access below the deck is limited, such as over deep water or rough terrain. For the same segment weight and length, overhead systems are often lighter and more economical than underslung alternatives, making them a preferred option when site conditions support their use.
Underslung Formtraveller
In an underslung Formtraveller the main structure is located beneath the deck, supporting the formwork from below. This arrangement is chosen when access from below is easier, or when height restrictions exist above the deck. Underslung Formtravellers can be modified for decks with steep longitudinal slopes by keeping the traveller horizontal during casting and allowing it to follow the slope during launching. Braking systems ensure safe positioning on steep gradients.
Arch Formtraveller
The arch Formtraveller is a specialised system for casting concrete arch ribs segment by segment. It supports the fresh concrete and formwork for each new rib section and transfers loads into the previously completed part of the arch. By precisely controlling geometry and camber, it enables high-accuracy construction of concrete arch bridges even where traditional scaffolding is impractical.
Wing Formtraveller
The wing Formtraveller is used to cast deck wings in both composite decks (steel girders with a concrete slab) and full concrete decks with wide cantilever sections. Using a dedicated wing traveller allows the formwork to be optimised and reused from span to span, improving speed and surface quality while the main traveller handles the core of the deck.
Formwork, Segment Length and Deck Geometry
Formtraveller systems include internal and external formwork tailored to the deck geometry. Formwork panels are typically about 5.8 meters long, matching a segment length of around five meters and allowing for necessary overlaps. The internal formwork is advanced on rails integrated into the traveller structure. This is usually done manually using chain tackles, though hydraulic systems may be used when required.
Internal and external formwork panels are linked through the deck webs with threaded ties, forming a closed box that resists hydrostatic pressure and maintains geometry. A common facing material is 21 mm phenolic plywood mounted on a reusable steel frame. Plywood can be replaced as needed, while the steel substructure remains suitable for many projects. Timber beams are often used in web formwork for flexibility.
Efficient operation requires attention to deck design. Internal diaphragms must be placed toward the rear of each segment to allow internal formwork to pass forward. Maintaining constant spacing between deck webs simplifies the formwork layout and improves operational performance.
Launching, Deformation Limits and Construction Cycle
A Formtraveller is typically launched at a speed of around ten meters per hour. Because most segments are only five meters long, higher speeds are unnecessary; precision and safety take priority.
A standard two-segment construction cycle lasts approximately one week. This duration varies depending on reinforcement assembly, prestressing operations, concrete curing times, and formwork preparation. Formtravellers are designed to streamline operations such as opening and closing the formwork, applying camber adjustments, and preparing for installation of reinforcement.
Structural deformation limits ensure accurate deck geometry. A global deformation limit of L/400 (where L is the span of the traveller structure) is common, while local formwork elements typically follow a limit of L/250.
Supports, Anchorage and Interaction with the Bridge
Formtravellers attach to the concrete deck via threaded bar anchors passing through block-outs in the bottom and top slabs. These anchors safely transfer construction loads during casting and launching. Prior to construction, the equipment’s weight and reaction forces are submitted to the bridge designer to verify that piers and deck cantilevers can resist all construction-stage loads.
Design Codes, Machinery Directive and Safety Systems
Formtraveller structures are designed according to the relevant Eurocodes and manufactured under EN 1090. Since the Formtraveller includes mechanical and hydraulic systems and moves during use, it is classified as a machine under the Machinery Directive. This classification requires comprehensive risk analysis and the integration of safety systems.
Hydraulic cylinders used for launching include safety valves that prevent piston movement in case of hydraulic failure. On steep longitudinal slopes, braking systems secure the traveller to the rails during movement. Proper planning, procedures, and training ensure a safe environment for all site personnel.
Assembly, Transport and Reuse
During fabrication, Formtraveller components undergo partial pre-assembly to confirm fit and alignment. All parts are marked to ensure efficient and error-free assembly on site. Components are sized for transport in standard 40-foot containers or on truck platforms, and detailed weight information is provided to allow correct crane selection and safe lifting.
After dismantling, the same Formtraveller can be transported and rebuilt for future projects with minimal modifications. With proper care and maintenance, a Formtraveller can remain in service for more than fifty years, offering excellent lifecycle economy and sustainability.
Teams and Project Organisation
Operating a pair of Formtravellers typically requires a team of eight to ten skilled workers. Their tasks include opening and closing formwork, carrying out launches, adjusting camber, assembling reinforcement, and conducting concrete pours. Full-scale load testing is rarely practical; instead, safety is ensured through detailed engineering calculations, modelling, and strict inspection procedures.
Evaluating and Tailoring a Formtraveller Solution
Each project begins with the preparation of a Design Criteria Document, which defines segment weights, loads, safety factors, wind conditions, maximum spans, materials, and other technical requirements. The performance, safety, and cost-effectiveness of the Formtraveller depend heavily on this document, which is developed in close coordination with the bridge designer and contractor.
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