Concept Design: Alfa Polaris; Xavier Font
Structural Design: Alfa Polaris; Xavier Font, Cristina Fernández
Security And Health: Trema Projectes; Andreu Gilaberte, Àngels Salvadó
Main Contractor: Excavaciones y Construcciones Benjumea; Albert Barrero Gil, Carlos Marín Suárez
Client: Municipio de Montornès del Vallès; Pere Pascual Mariné, Josep Pérez Amatller
Site Supervision: Municipio de Montòrnès del Vallès, asistido por Alfa Polaris
Text description provided by the architects. Montornès del Vallès is a municipality of 16,000 inhabitants in the metropolitan area of Barcelona. Montornès Centre is the main settlement, where most of the population —more than 12,000 inhabitants— live. However, a significant part of its residents —some 3,700— live in Montornès North, located just over a kilometer away.
The two urban areas are on opposite sides of the River Mogent, which crosses the municipality from east to west. So far, there was only one bridge to cross the river. The main goal of the construction of this new footbridge was to provide a new pedestrian path to reduce the length of the displacements between these two main districts, and at the same time provide a more friendly route for pedestrians and cyclists.
In essence, the project consists of three large objects: the deck over the river and the two access ramps. The three elements are of a comparable size and our intention was to provide them with similar volumes but highlighting, with an appropriate choice of materials, the contrast between them.
For the deck, a simple structural solution of a single 47.7-metre long span Corten steel truss girder was chosen. The proposed structure is formed by two longitudinal Warren truss girders linked together at their top and bottom flanges by horizontal Warren trusses.
The depth of the girders was fixed inferiorly by the geometric limitation established by the hydraulic requirements, and at the top by the minimum safety distance to the cables of a high-voltage overhead power line that passes through the center of the river.
The decking of the footbridge is placed over the lower horizontal truss so that the users walk inside a tubular element of rectangular section, of a functional width of 3.0 meters and a free height of 2.7 meters; an arrangement that offers a safer feeling against the proximity of the power line cables.
The choice of the truss typology provides a great transparency to the crossing and allows pedestrians to fully enjoy the views that result from the necessary elevation of the path. However, with the aim of attenuating the tunnel effect generated by this configuration, which might become somewhat claustrophobic, the upper horizontal lattice is interrupted in wide sections and appears only at its two ends and around mid-span, where, for structural reasons, is more necessary.
The Warren truss is a classic typology in the world of structures, which is sometimes perceived as an outdated form. For this reason, we transformed its shape introducing a marked irregularity to the rhythm of the trusses and we accentuated an intended effect of controlled chaos.
As a result, we provided pedestrians and cyclists a special user experience with a highly effective and very low maintenance structure, which, along with a careful selection of the rest of materials (gabions for the ramps, polymeric timber and electrowelded Corten steel grating for the decking, LED lamps for the street lighting,...), allowed us to achieve the sought goals with a highly cost-effective solution.