Fig. 6. Two different resistant scheme of the formwork travellers
single traveller to build the one single octagonal leg
of the arch.
practically zero
the morning).
The formwork travellers have two different resistant
frameworks for the two main operations they have to
carry out:
Technical Services of FCC developed a computer tool
for the geometrical control of the bridge in order to
take into account the construction and thermal
precambers in each segment.
a) Casting of a segment: The resistant scheme is
based on a cantilever beam connected to
the prior segment. For this end, the travellers are
formed by a main beam with variable depth
supporting the formworks used to cast
the segments. The connection of the travellers
are materialised with two supports on the prior
segment, one in compression and the other one
under tensile forces.
b) Advance movement to the next segment:
the movement is done by means of a hydraulic
system, reacting against the prior segment, both
on the top and the bottom of the arch, resulting
a repetitive movement similar to the expansion
and contraction used by worms.
On the other hand, thermal factors are essential to
control the geometry of the cantilevers during
construction. The construction precamber must be
amended taken into account the real temperature
of the arch concrete and of the stays, known thanks
to the bridge monitoring.
In order to avoid the movements in the arch due to
the thermal gradient in the arch (hardly evaluable
because of a huge depth), the geometrical control
was always done in a moment when the gradient was
at
first
time
in
3.4.3. Temporary steel tower
3.4.3.1 Description and operating mode
As mentioned, a temporary steel tower is needed to
be erected upon the main piers in order to get an
effective attack angle in the 16 last stay cables
families. The temporary steel tower was redesigned
by the Technical Services of FCC in the detailed
project, and its main characteristics are the following:
3.4.2. Geometrical control
In any bridge constructed by the successive cantilever
method,
the
geometrical
control
during
the construction is decisive to get the appropriate
geometry in the bridge axle after applying all the dead
load and keeping in mind the rheological effects. For
this purpose, construction precambers have been
considered analysing deeply the construction process
and the age of every segment.
(generally
-
The use of double-T profiles, in such a way it was
easy to assemble and the welded connections
had an easy access to inspect.
-
A hinge was designed as a junction between
the tower and the deck. Thus the tower could be
independent from the deck, and the moments
due to unbalances between forward and
retaining stay cables would not be transmitted to
the deck.
3.4.3.2 Tower lifting
As a consequence of the hinge implemented
in the base of the tower, a tower lifting procedure
was developed in order to assemble the tower in
a horizontal way and then raise the tower around
the hinge. This procedure achieved the reduction
of bolt connections (in a vertical way of assembling,
the tower should have been divided into more pieces)
and removed the working at heights.
The tower lifting procedure was developed by
the Technical Services of FCC in collaboration with
BBR (a subsidiary company of FCC). An auxiliary
structure shaped like a tripod was designed. This
structure anchored to the tower was pulled by means
of horizontal heavy lifting equipment, until
4/2016