Construction of precast concrete bridges with spans ranging
from 100 ft (30 m) to more than 600 ft (180 m) is
mostly based on the use of self-launching machines. The
launching units are complex and delicate structures. They
resist high loads on long spans under the same constraints
that the obstruction to overpass exerts on the final structure.
They are adaptable for reuse on different projects.
They must be as light as possible, which involves designing
for high stress levels in different load and support
conditions, and they are assembled and dismantled many
times and reused by different crews.