How bridges get built · Precast concrete decks · Crane erection of precast girders
Also called: crane placement, girder erection by crane, tandem lift
How it is done
- Prepare a lift plan for every span: heaviest girder at its radius, crane configuration, ground bearing pressure under tracks or outriggers (with mats), exclusion zones and the road or rail closures needed.
- Check the bearings for level and position, and inspect girders on delivery for camber, sweep, end-zone cracks and handling damage.
- Lift with one crane, or two in tandem, using the specified lifting points or a spreader, control swing with tag lines and stop at the wind limit in the lift plan.
- Land the girder on its bearings and brace it before the crane releases: the first girder of each span needs external bracing to the pier cap, and the next ones are tied to it.
- Repeat across the width, then install the end and intermediate diaphragms and permanent bracing; check girder stability under wind until the deck is cast.
- Survey the girder tops and calculate the haunch (build-up) for the deck profile, allowing for camber growth.
- Form and cast the deck slab and any continuity diaphragms, and remove temporary bracing only when the design allows.
Key numbers
- Span20–45 m typical; single-piece girders now reach about 68 m (Puyallup River Bridge, 2021)
- Girder weight40–150 t typical
- Tandem liftseach crane usually limited to about 75–80 % of its rated capacity
- Lateral stability (PCI method)factor of safety at least 1.0 against cracking and 1.5 against failure
- Rate4–10 girders per day once the cranes are set up
- Costdeck USD 800–1,300 per m2
Where it fits
- Overpasses, viaduct approaches, river bridges from the banks or a trestle, spans to about 45-50 m (55 m with two cranes), any site with crane access on both sides.
Where it does not
- Piers in water without a trestle or barge, heights over 30-40 m (crane capacity falls with radius), sites where girder transport cannot reach.
Choosing it
- Choose crane erection over a launching girder when cranes can stand at every span (or on the completed deck) and girder weights are within capacity at the required radius: cheapest and fastest for short viaducts.
- Prefer a launching girder over water, wetlands, railways or live roads, or where ground bearing for large cranes is poor, on viaducts of about ten spans or more.
- Choose a tandem lift over one larger crane only with a detailed lift plan; it saves crane size but adds coordination risk.
- Prefer spliced girders or steel when single-piece girders exceed transport or crane limits.
Plant, pace and money
PlantCrawler crane 250-600 t (or two), transport, bracing, deck formwork.
ProductivityOne to three days per span; a girder every 30-60 minutes once set up.
CostDeck USD 800-1,300 per m2; among the cheapest.
Risks and controls
What goes wrong
- Girder rollover before bracing (a recurring fatal accident), crane tipping on soft ground, lifting in wind, crane outriggers on the edge of an excavation.
Quality assurance
Lift plan for each span with ground bearing checks, bracing installed before the crane releases, girder camber checked before placing the slab.
Origins
Prestressed concrete girders reached the US with the Walnut Lane Memorial Bridge in Philadelphia (1950); the AASHO-PCI standard I-girders of the late 1950s and the bulb-tees of the late 1980s made precast girders erected by crane the default for short and medium spans.
Examples
The game's default approach-span method; most Korean, US and European highway bridges.
Case studies
Puyallup River Bridge (southbound I-5), Tacoma, WashingtonUSA · 202168 m (223 ft) WF100 girders, the longest prestressed concrete girders in the US at the time, trucked a few kilometres from the plant and lifted at night in windows coordinated with two railways.
Lake Pontchartrain Causeway, LouisianaUSA · 1956About 38 km of identical precast prestressed spans mass-produced on shore and set by floating cranes, an early demonstration of assembly-line precast erection.
In the bridge game
What Bridge Master applies when you pick it
Deck types: PSC I-girder, PSC U-girder, Voided slab, Spliced PSC girder, Timber deck, FRP deck, Precast segmental box, RC slab, Steel plate girder, Steel box girder. Spans 20-45 m, up to 60 m.
- +25: Cranes can stand at the piers: just lift them in.
- +15: Night lifts from the verge or in a possession.
- -40: Cranes cannot stand in water; launcher or barge.
- -30: No crane positions; use a launching girder.
- -25: Tall piers exceed reach; launcher.
- -20: Very heavy girders need large tandem cranes.
- -40: Water under the span: a ground crane needs a trestle or crane barges here; a launcher or floating crane is the usual answer.
- not allowed: Land crane erection over deep water.
Related methods
Launching girder (beam launcher) for precast girdersPrecast girder casting and prestressing bedsDeck slabs on girders: cast-in-place, precast panels and stay-in-place formsCrane erection of steel girdersFull-depth precast deck panels with UHPC or grouted jointsContinuity over piers for precast girders: stitch pours, diaphragms and link slabs
Further reading
PCI Bridge Design Manual · FHWA girder stability guidance · ASME B30.5 · PCI Recommended Practice for Lateral Stability of Precast, Prestressed Concrete Bridge Girders · Mast, Lateral stability of long prestressed concrete beams (PCI Journal)