Construction methods · Precast concrete decks

Crane erection of precast girders

Precast I, U or bulb-T girders are lifted from the truck onto the pier caps by one or two mobile or crawler cranes standing beside the bridge, then a deck slab is cast on top. The most common bridge construction on earth for spans of 20-45 m wherever a crane can stand.

How bridges get built · Precast concrete decks · Crane erection of precast girders

Also called: crane placement, girder erection by crane, tandem lift

girder on bearings, braced at oncecrane on firm ground beside the bridgeCrane erection of precast girders
Concept diagram (TheBridgeEng)

How it is done

  1. Cast girders in a yard (30-50 m, 40-120 t); transport by truck or barge; stage at the site.
  2. Position the crane on firm ground at each span; lift each girder to the bearings, brace it laterally at once (girders are unstable alone), repeat across the width.
  3. Place diaphragms and precast or cast-in-place deck slab; the slab makes the girders composite.

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.

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.

Examples

The game's default approach-span method; most Korean, US and European highway bridges.

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 15-45 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.
  • not allowed: Land crane erection over deep water.

Try it in the game →

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 girders

Further reading

PCI Bridge Design Manual · FHWA girder stability guidance · ASME B30.5

Launching girder (beam launcher) for precast girders →