What is a Launching Gantry?

A launching gantry (LG) is a large steel structure used to erect precast concrete segments into spans on viaducts and bridges. It spans two or more piers and acts as a travelling crane and support frame. After completing one span, it launches forward on rails to the next pier position.

Two main types:

• Overhead gantry (OLG): Sits above deck level. Segments fed from below or from sides.
• Underslung gantry (ULG): Hangs below deck level. More suited for curved alignments.

Typical cycle: Pier segment → progressive segment assembly → closure → stressing → bearing transfer → gantry launch. One span per 5–10 working days depending on team, geometry, and logistics.