In the case of the deck-arch bridge option, and
starting with the premise of not setting temporary
piers inside the reservoir during construction either,
three erection alternatives were studied (Fig. 4):
pylon-method cantilever erection of the arch using
temporary cable stays and provisional pylons over the
piers adjacent to the arch (4a), truss-method
cantilever erection using the arch as the lower chord
of two great truss cantilevers where the deck of the
bridge is the top chord (4b), and a variation of the
latter where the top chord of the truss is formed by
temporary ties that would be removed after the
completion of the arch (4c). Another sub-alternative,
compatible with all these three erection possibilities,
was studied: the lifting of an auxiliary 120-m-to-180m-long truss for the construction of the central part of
the arch (4d).
Among the different erection solutions that were
studied, all of them feasible and successfully used for
the construction of other long-span arch bridges, the
cantilever method with the help of temporary towers
(and without flotation) was chosen as the most
appropriate in this case. Although this alternative
needs more provisional members than others, it
allows a more precise geometrical control during
erection and, in addition, introduces a precompression force in the arch that helps to partially
compensate its elastic deformation under permanent
loads. This makes unnecessary a final jacking
operation in the crown of the arch once the two
cantilevers meet, that would be essential with other
erection procedures.
Fig. 4a: Construction alt. 1. Pylon-method cantilever erection of the arch using provisional pylons
Fig. 4b: Construction alt. 2. Truss-method cantilever erection using the deck as the top chord
4/2016