Erection method:
The variety of erection methods used
for bridges is too wide to be covered in detail here.
The method selected depends very much on the type of bridge construction, span,
height above ground or water etc.
Commonly used methods for the
erection of bridges:
1. In-situ - assembly of bridge
components on temporary false work.
2. Lifting - e.g. (a) beams and
trusses - placing of individual beams or a complete deck by crane (b)
suspension bridges - lifting of pre-fabricated deck modules which are then hung
from the deck hangers connected to the previously installed main cables, slung
between the main towers and anchorages.
Box girders lifted individually for
a river bridge at St Nazaire, France
3. Launching - sequential
construction (on rollers or tracks) of a continuous deck at one end of the
bridge. As each new section is added the whole deck is pushed or pulled out
(usually over multiple spans).
4. Sliding or rolling - construction
of a complete new bridge (usually alongside a busy existing bridge) which is
then jacked into place over a few hours or days, to replace the existing
structure.
5. Cantilevering - (a) for arches -
successive construction from the two springing points which is temporarily tied
back until the two halves can be joined at midspan (b) for cable-stayed bridges
- successive cantilevering out from the pylons of deck units suspended from the
stay cables.
