Civil Engineering Reference
In-Depth Information
were 12 mm diameter with 12 mm lacers inside the links. Over 5,000 beams were
required.
The beams were made principally in one main precasting yard, Figure 10.18,
equipped with 24 steam cured steel moulds, designed to produce one beam per day per
mould. The reinforcement was prepared in jigs and placed in the mould. The concrete
was cast in the evening and cured overnight. A light fi rst phase of prestress applied
next morning allowed the beam to be lifted clear of its mould and placed in a storage
area, awaiting the complement of the prestress. As the site was crossed by three large
rivers, there were some problems of access, and several smaller strategically placed
yards were also employed.
Purpose-built launchers were designed to place all fi ve beams of a deck within two
days. The slabs between beams were cast using a launching gantry that carried the
formwork for three consecutive spans. This gantry was articulated so that it could
adapt to the horizontal and vertical curves of the highway alignment. The precast end
diaphragms of the decks were designed to allow the gantry to pass above them.
Most of the piers consisted of a crosshead carried by two columns, each resting
on a single bored pile, although at interchanges single columns with crossheads were
also used, Figure 10.16. Groups of nine spans were linked together by short lengths
of 180 mm thick cast-in-situ slab, Figure 10.17 (c), to improve the ride and reduce
maintenance (
7.15.2
). For this reason the ends of the webs were sloped forwards, to
provide suffi cient length for the link slab to defl ect under the effect of the defl ection of
the beams and of the small vertical compression of the elastomeric bearings.
The 17 km of viaduct were completed in 21 months from the installation of the
fi rst pile.
Figure 10.18
GSZ Superhighway, Pearl River Delta Viaducts: main casting yard (Photo:
Benaim)
