A bridge for our high speed train

General view of the construction (upper image).
Reinforcement of the hinges of the arch (lower image).

The most beautiful bridge for the Galician high speed train was finished successfully and I was there, having a look and talking to our on-site partners that usually give advice to the contractor. It was concluded by laying down the two halves of the central arch last December. The bridge is placed in a rural valley close to Santiago de Compostela.

As one of my on-site colleagues explained us, the arch serves to create a fixed point to resist the horizontal braking forces from the deck. Without the arch, an enormous abutment would be necessary. Undoubtedly the arch also helps to improve the visual impact on the landscape.



Video of the lowering stage. Heigth of the arch = 80 m, Span of the arch= 120 m, Time = 2 days.

View of the deck from the ground (left). My colleagues and I having a look (right).

Building an arch bridge is always tricky since the structure is completely unstable until the two parts meet in the middle. In this particular case, the arch was cast and laid using a German cable stayed system over the head of the closest pier and tensioned from the base of the next pier. Once the two semi-arches were connected by a hinge joint at the key to form a three-hinged arch, the key and arch springs were concreted to reduce this to a two-hinged structure. Displacements of the arch and the head of the pier have been computed in a quite sophisticated way for each time step. Unfortunately, real behaviour can be more complicated than the most complicated theory and the sophisticated calculations of the deformations barely coincided with the real ones.

Usually arch bridges employ vertical supports (a.k.a. spandrels) to distribute the vertical loads of the deck to the arch below, but the Natchez Trace Bridge was designed without spandrels to create a more open and aesthetically pleasing appearance and, indeed, that bridge has strongly influenced the contemporary bridge design.

Picture from the edge of the deck.

I am confident that these infra-structures will provide positive possibilities for the residents of Galiza. New business opportunities will inevitably be created as investors from Madrid and the North West can open up new commercial ties. It is true that we Galicians/Spaniards are not a train culture but perhaps things may change if we can enjoy the fast and affordable transportation of our French and German neighbours.

Note: I did not publish this post in December due to the odd requirement of confidenciality although the process was seen from all the places of the valley and, in fact, lots of videos were recorded and uploaded by the villagers. Copying pictures without a polite acknowledgement is not allowed .