How bridges get built · Cable-supported and arch bridges · Float-in of complete arches and spans
Also called: float-in erection, barge-assembled arch, whole-span float-in
How it is done
- Assemble the span on barges or on a bank slipway; complete the deck and surfacing where weight allows.
- Tow at slack water; position over the piers with winches and tugs; ballast the barges down or jack the span onto the bearings.
- Connect and release the barges before the tide turns.
Where it fits
- Tied arches and trusses of 100-300 m over navigable water, harbour crossings, replacement spans.
Where it does not
- Rough water, sites without an assembly area, spans too heavy for available barges.
Plant, pace and money
PlantBarges 5,000-20,000 t, tugs, ballast systems, winches, weather forecasting.
ProductivityMonths of assembly, one day of float-in.
CostAssembly on the bank is cheaper than in the air; the marine operation USD 1-5 million.
Risks and controls
What goes wrong
- Weather during the tow, barge stability, misalignment on landing.
Quality assurance
Naval architecture check of the tow, float-in procedure with abort criteria, survey on landing.
Examples
Fremont Bridge (Portland) centre span, several Dutch and German river arches, Chinese Yangtze tied arches.
In the bridge game
What Bridge Master applies when you pick it
Deck types: Steel arch, Steel truss, Steel box girder, Network tied arch. Spans 100-250 m, up to 300 m.
- +30: Tied arch over a channel: float it in.
- -45: No draft for barges.
Related methods
Floating crane erectionSPMT move (self-propelled modular transporters)Lateral slide (slide-in bridge construction)Network tied arch construction
Further reading
Rosignoli · PIANC guidance on marine operations