How bridges get built · Steel erection · Launching of steel girders and boxes
Also called: steel launching, incremental launching of steel, push launching
How it is done
- Assemble the girders on a launching bed with rollers; attach a launching nose and, for long spans, a king post with stay cables.
- Push with hydraulic jacks or pull with strand jacks at 10-30 m per hour; guide laterally at each pier; monitor deflection and pier friction.
- After launching, lower onto permanent bearings, remove the nose and temporary members, then place the deck slab.
Where it fits
- Straight or constant-curvature bridges over rivers, valleys, railways and motorways; spans 40-120 m; sites with room for the assembly bed.
Where it does not
- Variable depth girders, tight curves, sites without the bed length.
Plant, pace and money
PlantLaunching bed and rollers, jacks or strand jacks, nose, king post, lateral guides.
ProductivityA launch stage per 1-3 days; assembly governs.
CostErection USD 250-500 per tonne.
Risks and controls
What goes wrong
- Web crippling at the roller under the cantilever, lateral drift, nose landing, uplift at the rear.
Quality assurance
Web patch loading checks at each launch position, survey of the nose approach, friction monitoring.
Examples
Millau Viaduct (steel deck launched from both sides with a mast), many German and Korean railway bridges.
In the bridge game
What Bridge Master applies when you pick it
Deck types: Steel plate girder, Steel box girder, Orthotropic steel box, Steel truss, Steel arch, PSC box (cast in place). Spans 40-120 m, up to 160 m.
- +30: Steel over water, rail or valley: launch it.
- +20: One short possession for the nose passage.
- -40: Cannot launch variable curvature.
- -15: A crane would do it faster.
- not allowed: Steel launch on a variable-radius alignment.
Related methods
Further reading
Rosignoli, Bridge Launching · SETRA steel bridge launching guide