3. THE DESIGNED BRIDGE
The viaduct is formed by three distinct areas: two
sequences of approaching spans from both banks, and
the main span. The span arrangement of the former is
36m + 6 x 45m (towards Madrid), while that of the
latter is 7 x 45m + 36 m (towards Portugal). The great
384m deck-arch main span gives support, by means of
spandrel columns (45m + 6 x 42m + 45m), to the
upper deck, which has a continuous multi-supported
prestressed box-girder scheme all along the viaduct.
The deck is a double-cantilevered prestressedconcrete box girder with a constant depth of 3.10 m
and a width of 14 m (allowing the arrangement of a
conventional double-line HSR platform). The inherent
flexibility of the arch makes the deck require, when
over the reservoir, greater ratios of prestressing and
reinforcing steel and a higher grade concrete (C60/75
as against C40/50). This is despite the span reduction
between the spandrel columns (42m as against 45m).
The arch is made of self-compacting and high-strength
high-performance concrete (C80/95). It has an
octagonal hollow section with variable depth and
width in central 210m section, from where it splits
into two legs with an irregular hexagonal section down
to the springings. Both legs are linked together under
the first (7 and 14) spandrel columns (Figs. 5, 7 and
8b,c,d). The arch has a depth of 6.90m at the
springings, the horizontal distance between side faces
being 19.00m, and has a depth of 4.80m and a width
of 6.00m at its crown, this distance being coincident
with the lower width of the deck, to which it is linked,
making up a single concrete cross-section, in the
central 30m (Fig. 8e).
Both piers and spandrel columns have a variable
octagonal hollow shape with a top solid area. Their
heights range from 12m (pier 22) to 65.30m (pier 15).
Abutments are U-type with wing walls.
Every element of the bridge in contact with the terrain
has a shallow foundation on rock with spread footings
except for the arch and its adjacent piers which are
founded with massive concrete elements (Figs. 5, 6
and 8a,b,c,d). The latter have an irregular polyhedral
shape with a cascade configuration at their bottom
areas due to the need to conform, in the most
optimum way, to the direction of the resultant archpier forces and to the variation in the depth of the
sound rock stratum. The cable-stayed system needed
for the erection of the arch requires tempor