Full-span precast erection (high-speed rail type)

How bridges get built · Precast concrete decks · Full-span precast erection (high-speed rail type)

Also called: full-span method, FSM precast, span carrier and launching gantry

How it is done

Set up a casting yard beside the alignment with several moulds (hydraulic inner forms), cage jigs, steam curing and storage pedestals, able to stay several spans ahead of erection.
Cast and cure each span, apply initial post-tensioning in the mould so it can be moved, and complete stressing and grouting in storage.
Lift the span with the yard's gantry cranes onto the rubber-tyred span carrier.
Drive the carrier along the completed viaduct, checked for its axle loads, to the erecting machine at the front.
The erecting machine takes the span, moves it forward and lowers it onto bearings that are then grouted, with levelling controlled at three or four support points.
Advance the machine to the next pier, often helped by the carrier, and repeat.
At the end of a section, dismantle and transfer the machine and carrier, or turn them for the parallel line.

Key numbers

Span20–40 m (32 m is the Chinese high-speed rail standard, with 24 m for shorter spans)
Span weight600–1,000 t (Chinese 32 m double-track box about 900 t)
Erection1–2 spans per day per set, about 10–20 km of viaduct per year
Break-evenhundreds of identical spans per yard
Costdeck USD 900–1,400 per m2 at high-speed-rail scale

Where it fits

Straight or gently curved viaducts with hundreds of identical spans, rail, flat terrain, no ground access.

Where it does not

Fewer than about 100 spans (the yard and carrier cannot be amortised), spans over 40-45 m, tight curves, tall piers beyond gantry reach.

Choosing it

Choose it over span-by-span segmental when hundreds of identical spans run along a straight or gently curved corridor and the programme needs 10 km or more of viaduct a year per front.
Prefer span-by-span segmental where 600–1,000 t spans cannot be moved, curves are tight or spans exceed about 40 m.
Prefer an MSS or launching girder where span numbers are moderate.

Plant, pace and money

PlantCasting yard, span carrier, launching gantry (900 t class), steam curing.

ProductivityOne span per shift; 10-20 km of viaduct per year per set.

CostDeck USD 900-1,400 per m2 at high-speed-rail scale; uneconomic below it.

Risks and controls

What goes wrong

Gantry and carrier overturning, mould geometry error repeated hundreds of times, span cracking during transport.

Quality assurance

Mould survey, curing records, span camber and dimensions before dispatch, gantry procedures.

Origins

Placing whole precast spans is old in marine work (Lake Pontchartrain Causeway, 1956; Great Belt West Bridge, 1990s); the land version with a span carrier and erecting machine became the standard viaduct method of Chinese high-speed rail from the mid-2000s.

Examples

Chinese high-speed rail viaducts such as Beijing-Shanghai, where the method built thousands of identical 32 m spans; marine versions with floating cranes on the Great Belt West Bridge.

Case studies

Beijing-Shanghai High-Speed RailwayChina · 2011Its long viaducts, including the 164.8 km Danyang-Kunshan Grand Bridge, are built mainly of 32 m precast boxes placed by carriers and erecting machines.

Great Belt West BridgeDenmark · 1990sMarine variant: concrete box spans of about 110 m cast whole on shore and set by the heavy floating crane Svanen.

In the bridge game

What Bridge Master applies when you pick it

Deck types: Full-span precast box, PSC U-girder, PSC I-girder. Spans 25-40 m, up to 45 m.

+35: Kilometres of 25-40 m spans: full-span precast with a deck-running gantry.
+15: Marine or urban viaduct with no ground access.
-40: Gantry and yard cannot be amortised.
-20: Gantry geometry on tight curves is awkward.
-40: Full spans past 45 m weigh over 1,000 t: beyond the gantry.
not allowed: Full-span precast beyond 55 m.

Try it in the game →