How bridges get built · Precast concrete decks · Launching girder (beam launcher) for precast girders
Also called: beam launcher, girder launcher, overhead girder erector
How it is done
- Assemble the launcher (1.5-2 spans long) at the abutment; support it on pier brackets or the pier caps.
- Deliver girders along the completed deck; the winch trolleys lift, traverse and lower each girder onto its bearings.
- After the span, self-launch to the next pier using the rear support as a counterweight; cycle.
Where it fits
- Viaducts with 25-45 m spans over water, wetlands, railways, urban roads; more than about 8-10 spans; wetland viaducts (with top-down delivery).
Where it does not
- Very short viaducts, spans beyond the launcher's rating, girders wider or heavier than the trolleys allow.
Plant, pace and money
PlantLaunching girder 60-100 m, 200-400 t, pier brackets, deck transport bogies.
ProductivityOne span per one to three days.
CostLauncher USD 1.5-4 million; erection USD 60-150 per m2 above crane erection.
Risks and controls
What goes wrong
- Launcher instability during self-launch, bracket failure, girder swinging in wind.
Quality assurance
Launch procedure, bracket load checks, wind limits.
Examples
Sea viaducts in the Gulf, Bangkok elevated expressways, Chinese high-speed rail approaches.
In the bridge game
What Bridge Master applies when you pick it
Deck types: PSC I-girder, PSC U-girder, Steel plate girder, Spliced PSC girder, Precast segmental box, Steel box girder, Voided slab, Full-span precast box. Spans 25-45 m, up to 55 m.
- +30: No ground access, many spans: beam launcher.
- +20: Top-down over the wetland.
- -30: Too few spans.
- -15: Cranes would be cheaper.
- -20: Launcher struggles on tight curves.
Related methods
Crane erection of precast girdersSpan-by-span precast segmental with gantryTop-down construction over wetlands
Further reading
Rosignoli, Bridge Construction Equipment