Structural monitoring of the Iris railway viaduct in Belgium

In order to expand the existing end station for railway connections to the Brussels Airport in Belgium, the Diabolo project was created. One of the largest structures built in this project was the “Iris” railway viaduct. The viaduct has a total length of approximately 800 m and the piers consist of a high vertical shaft supporting a system of six curved branches. Because of its rather unusual design, load tests were carried out with two freight trains. During these tests, strains and acceleration measurements were performed. This not only indicated that the theoretical calculations are conservative, but also reflected the complex structural behaviour. The piers seem to be very stiff but still have the capacity to distribute the braking and acceleration forces across the bridge. Finally, the long-term behaviour is observed indicating the importance of the daily temperature variations in the bridge design.