Civil Engineering Reference
In-Depth Information
Figure 17.20
Construction of Yajisha Bridge (Photo: Engineer Leo K.K. Leung, Executive
Director of Hopewell Highway Infrastructure Ltd (Hong Kong Stock Code:
737))
steel. Once this pre-arch had been closed, the steel falsework could be removed and
the box was extended by adding two side cells.
Arches may also be prefabricated in sections weighing hundreds of tons, and
assembled in cantilever using cable cranes. The Chinese have signifi cant experience of
this type of erection. Another method of erection for large-span arches used extensively
in China is to erect a pre-arch consisting of steel tubes braced together which are
subsequently fi lled with concrete that acts compositely with the tubes. The tubes are
erected in cantilever with tie backs, or by cable crane. Clearly the falsework is much
lighter than that required for the erection of the fi nished arch.
A recent example of this method of construction is the 360 m span Yajisha (an
alternative rendition of Ah Kai Sha) Bridge over the Pearl River close to Guangzhou,
Figure 17.20. Half arches consisting of steel tubes were built on falsework on either
bank, and then rotated about a vertical axis into their fi nal position. During the rotation,
the steel half arches were counter-balanced by short concrete arches supporting the
approach span. Once in position, the steel arches were fi lled with concrete [4]. This
single-deck dual-carriageway bridge was built instead of the Ah Kai Sha twin-deck
four-carriageway cable-stayed bridge designed by Benaim (
18.4.11
)
.
Yet another method of building large arches is to build each half arch vertically
over the springings, and then to rotate them about a horizontal axis, lowering them
into position. This requires restraining falsework of similar capacity to that required
by cantilever erection, but for a much shorter time. The construction of each half arch
may be carried out by slip-forming or jump-forming techniques that may be more
economical than building in cantilever.
When an arch is built in cantilever, the temporary masts and cables have to carry
the full weight of the arch before it is joined. These costly temporary works may be
signifi cantly reduced by building a structure that is hybrid between the arch and the
truss. The total restraining bending moment needed to ensure stability is of course
