Fig. 7. Lifting procedure and temporary steel tower working
the vertical position of the tower was achieved. This
manoeuvre was performed in less than one working
day.
3.4.4. Arch closure
One of the most challenging operations was the arch
closure. The main purpose of closure operations in
bridges built by the successive cantilever construction
method is to nullify the differential movements
between both cantilevers during the casting
of the key segment in order to avoid the cracking.
The closure was performed in August 2015, one
of the warmest and sunniest times of the year in
the location of the bridge. In August,
thermally-induced daily movements were at their
greatest.
prestressed before the effects of solar radiation
appeared.
This structure was set in place on 4 August 2015 and
the closing segment was cast on 6 August 2015.
The operation was successful and the relative error
between the two cantilevers at the key and
the absolute error after that operation were both
under 10 mm.
3.4.5. Self-Compacting Concrete with high
compression strength
There are three circumstances which make the use
of self-compacting concrete in the arch of Almonte
viaduct essential:
-
The variable and complicated geometry
of the arch makes the vibration of the concrete
impossible in so many points.
-
The huge density
the segments.
-
The required formwork of the upper face
of the arch makes impossible the cast
of a segment without a self-compacting
concrete.
These daily movements ranged as follows:
Daily stay cable heating was at its most intense.
Thermal daily variations of up to 24°C were
recorded in the cables, generating downward
movements of up to 120 mm.
Daily transverse solar radiation on the cantilever
was also at its most intense, inducing horizontal
movements of around 60 mm between 9:00 AM
and 11:00 AM.
A steel structure consisting in four longitudinal
double-T profiles positioned in the key segment near
each corner of the cross section of the arch was
designed to reduce these relative movements.
The chosen moment of the day to perform the arch
closure was between 6:30 AM and 9:30 AM, time lag
with the lowest thermal gradient when
the movements could be decreased to minor values.
In that short time lapse, the temporary struts were
received with high-strength, quick-setting mortar and
of
reinforcement
in
On the other hand, arches are elements submitted to
huge axial forces due to their natural resistant
scheme, so high compression strength concrete is
required. Furthermore characteristic resistance of 40
Mpa was needed at early age (12 hours) in order to
optimize the working cycle, advancing the travellers in
less than two days since casting of a segment.
The self-compacting concrete used at the arch
of Almonte viaduct have a characteristic resistance
of 80 MPa at 28 days. The selected material and its
main characteristics are the following:
4/2016