The Arbizelai Viaduct is situated on the stretch between Arrasate and Eskoriatza of the new Deba Motorway linking Vitoria-Gasteiz and Eibar, near the town of Arrasate-Mondragón.

The main difficulty of this viaduct is the passage over the Deba River and over the south link of the current road to Mondragón. The main difficulty of this viaduct is the crossing over the river Deba and the South Junction of the road that currently gives access to Mondragón. The viaduct spans the junction roads and the river at a strongly oblique angle. There is an additional difficulty posed by the fact that the river and the road branches are situated close together, which compelled us to design a 140 m long main span of the viaduct.

This unique span leads to a mixed structure solution with a single deck for the two roadways, with a single central metal box with an upper slab and large lateral concrete cantilevers, supported on metal brackets. The caisson is supported on single piles, open at the head to give transverse stability to the deck.

The viaduct is 424.32 m long, with seven spans of the following distribution: 31.20 + 46.80 + 59.28 + 59.28 + 140.40 + 49.92 + 37.44 m. The deck is a composite, continuous girder of a 2.65 m depth, constant along the entire viaduct, composed of a steel, double-cell, trapezoidal box girder, 9 m wide at the bottom side, and an upper concrete slab. Around some supports we also used a lower concrete slab on top of a steel plate in order to increase the effectiveness of the section.

The deck is widened at one end of the viaduct from 25.20 meters wide to 27.37 meters; This translates into an increase in side overhangs, because the metal box remains the same dimensions; With this width, the side overhangs from the edge of the caisson are more than 7 meters; They have been resolved with inclined metal brackets located every 3.12 meters, which start at the lower edge of the box and support the concrete slab near the end of the cantilever.

The continuous girder of a constant depth is cable-stayed both in the main span and the two adjacent ones by means of stay cable fans placed along the bridge axis. The cable staying is anchored to two towers situated on the median strip, each formed by a single vertical pier. The towers are made of steel and filled with self-compacting concrete. The viaduct has a curved plan with a radius on the order of 1,000 m. This curvature has the most impact on the structure in the transverse bending in the towers.