Civil Engineering Reference
In-Depth Information
15.5.10 Erection by overhead gantry
Gantries are employed to erect viaducts on high piers, in cities or over water. Generally
a gantry will fi rst erect the pier segment, launch itself forwards to rest on this segment,
receive segments delivered along the deck of the erected viaduct and erect them in
balanced cantilever while stabilising the deck. The size, complexity and degree of
mechanical sophistication of a gantry depend principally on the maximum span of
the deck, on the weight of the segments to be handled, on the radius of curvature to
be negotiated, on the rate of construction planned and on the combinations of these
factors, Figure 15.32.
A pier head falsework is required to carry the pier segment, and to provide a support
to the front leg of the gantry. This falsework may be supported off the pile cap, or may
be attached to the pier head. Figure 15.33
shows the pier head falsework being load
tested by pulling it upwards; the steel beams above the pier belong to the testing rig
and are not part of the pier head falsework.
In the majority of projects, the gantry applies loads to the deck as it launches itself
forwards. As gantries weigh between 150 tons and 400 tons, the decks need to be
Figure 15.32
STAR Viaduct: gantry erection (Photo: Benaim)
