Form travellers and traveller anchorage

How bridges get built · Cast-in-place concrete decks · Form travellers and traveller anchorage

Also called: cantilever form traveller, traveller, CFT

How it is done

Select the traveller: an overhead truss (simple, handles variable depth) or an underslung frame (keeps the deck top clear for stays and cranes); size it for the heaviest segment and keep its self-weight low to limit the unbalanced moment.
Assemble the pair back to back on the pier table, fix the rails and anchor them with high-strength bars through the deck; load-test the traveller or monitor the first pour against predicted deflections.
Advance: release the forms from the cast segment, lower the soffit, release the rear anchors and roll forward on the rails with hydraulic cylinders, symmetrically on both cantilevers.
Re-anchor: install and stress the anchor bars to the specified force and record it (hold point before any load goes on).
Set the forms to the casting curve (theoretical profile plus predicted deflections), confirm by survey, then fix reinforcement and ducts and pour.
Compare the measured traveller deflection with the prediction after each pour and recalibrate the casting curve.
At the end of the cantilever, use one traveller or a closure frame for the closure pour, then roll the travellers back to the pier and lift them off or lower them to a barge.

Key numbers

Capacitysegments of about 100–250 t and 3–5 m length
Self-weightroughly 0.3–0.6 of the heaviest segment
Cycle5–9 days per segment; 4–5 days with prefabricated reinforcement and accelerated curing
Anchorshigh-strength bars of about 1,030–1,100 MPa stressed to a specified force every cycle
CostUSD 0.5–1.5 million per pair

Where it fits

All cast-in-place balanced cantilever decks, extradosed bridges, cable-stayed concrete decks cast on travellers with stays supporting the tip.

Where it does not

Unchecked anchorages; overloading the traveller with stored materials.

Choosing it

Choose an overhead traveller for conventional variable-depth box girders: simple and easy to access.
Choose an underslung traveller when the deck top must stay clear (stay anchorages, cranes, reinforcement handling) or for cable-stayed concrete decks cast with stay support at the tip.
Prefer hiring or reusing travellers when the segment geometry fits; a lighter traveller reduces the unbalanced moment and the pier table design forces.
Prefer precast segments with lifting frames when there are enough spans for a yard and segments can be delivered.

Plant, pace and money

PlantTraveller pair per pier, hydraulics, rails and anchor bars.

ProductivityThe traveller cycle of 5-9 days sets the pace of the cantilever.

CostUSD 0.5-1.5 million per pair.

Risks and controls

What goes wrong

Anchorage failure and traveller drop, wind, rail misalignment during rolling.

Quality assurance

Load test, anchor bar tension checks every cycle, wind limits for rolling.

Origins

Developed by Dyckerhoff & Widmann under Ulrich Finsterwalder for the Lahn bridge at Balduinstein (1950–51), together with the high-strength threaded bars used both for prestressing and for anchoring the traveller.

Examples

Every balanced cantilever in the game's construction animation.

Case studies

Lahn Bridge, BalduinsteinGermany · 1951The first prestressed concrete bridge built by balanced cantilever with form travellers and threaded bars.

Raftsundet BridgeNorway · 1998298 m main span cast segment by segment from form travellers; with Stolma, the longest concrete cantilever spans.