The Eighth Bridge over River Urumea is proposed as a replacement of the existing bridge located in the area Enea-Txomin LM.06 in the city of San Sebastian.
Its total length, 59.4 m, has been divided into two spans of 42 m and 17.4 m, with a single pier located on the left bank, outside the mainstream of the Urumea river, which improves the hydraulic performance and reduces foundation cost.
It has been provided a useful section on the bridge of 18.3 m with a central 7 m carriageway with two lanes of 3.2 m and a 30 cm curb, a cantilevered sidewalk of 4 m downstream, and an overhang of 5.5 m formed upstream with a 3 m sidewalk outside and a cycle lane of 2.5 m.
The overhang sidewalks are separated from the roadway by structural barriers 90 cm wide that host the main beams of the structure or edge ribs.
The core board, 8.8 m wide, includes the roadway and the main structure.
The metal beams or edge ribs on the sides have a width of 192 cm, 75 cm below and 117 cm above the deck, forming barriers between the road and the sidewalks. This configuration resolves at the same time the need to reduce hydraulic gauge, the height below the deck and also the apparent depth of the deck, so the result is a very slender structure. The edge beams are connected together by transverse steel diaphragms, on which the platform is embodied as a concrete slab.
Noteworthy is the fact that the plant of the bridge is its most unique feature, as the sidewalks diverge of the steel cantilevers as independent footbridges in the lateral span of 17.4 m, which gives them independence from the central core of the board to form paths on the side walkways. Thus, through the plant configuration, it also highlights the asymmetric distribution of the span on the bridge.
The other unique element of the bridge is its pile, located at 17.4 m from the abutment 1 to avoid interference with the river, is configured as its sculptural volume in concrete with metal core, curved surfaces also improves the flood hydraulic profile. It consists of two arms in V form attached to an overhead beam that acts as a diaphragm between main beams on the board at that point.
For its part, the abutments are integrated as an extension of the walls on the river banks, to carry out the re-urbanization of the area and the riverbed.
In conclusion, the result is an integrated bridge to fit the river bed of the Urumea, organized around its only pier, asymmetrically framing the river crossing, with an also asymmetrical deck plan organization separating pedestrian traffic from road traffic in a functional and also aesthetical way.