Fig. 10: Wind tunnel test analysis both in construction and final stages
4.2 Wind tunnel analysis
5. CONSTRUCTION
The main span of the viaduct goes significantly beyond
the 200m set by the Spanish code IAPF-2007 as a limit
after which aeroelastic effects must been taken into
account. It was noticed, during early stages of the
design, that the high flexibility of the bridge,
consequence of its main span, led to reduced values
of the first vibration frequencies (under 0,30 Hz)
which is indicative of its sensitiveness to these effects.
This fact, together with the three-dimensional
configuration of the structure and the complex
orography of the surrounding terrain, made it
essential to carry out, during the design stage, tests
using full-bridge aeroelastic models of the maximumcantilever construction stage and of the finished
bridge (in addition to section models). These models
were tested by Oritia & Boreas in the Boundary Layer
Wind Tunnel II of the University of Western Ontario.
The construction of the bridge, which started in
August 2011, was carried out with exactly the same
erection sequence as the one considered during the
project stage. The arch is built by pylon-method
cantilever construction with temporary cable-stays
(using steel towers and underslung form travellers
specially designed for this bridge). The first cable-stays
use the adjacent piers as a pylon (Fig. 11). During the
erection of the arch, the prestressing forces of the
cable-stays must be controlled and adjusted, untensioning several of them in some stages. The deck is
erected using overhead cast-in-situ movable
scaffolding system.
Wind tunnel analysis has permitted to determine the
specific wind static loads to be used in this bridge, to
validate the appropriate behaviour of the proposed
cross-sections (revealing the importance of the
aerodynamic shapes used in arch and spandrel
columns) and to confirm the good overall response of
the design.
A detailed analysis of all the erection phases of the
arch with the real bridge-building equipment was
performed together by the designers and the
technical department of the contractor during the
construction stage. A complete monitoring
programme was developed to control every step of
the process.
4/2016