Can Gili Footbridge

Construction year: 2010
Address: Carrer de Sant Fermí | GRANOLLERS | Spain
Latitude/Longitude: 41.6127, 2.27527

The construction of this footbridge was an old claim of the inhabitants of the two neighbourhoods separated from one another by the trench of the BV-1432 road. These two residential areas, Terra Alta on the south bank and Can Gili on the north one, have a different nature: Terra Alta is a low density urban area, with a community park, but with no services, and Can Gili is a dense zone with shops and community services, but no green areas.

So far, people from one neighbourhood wanting to go to the other one had to make a detour, crossing the road through a highway bridge, placed at the east border of these urban areas, with a single narrow footway in one of the sides of its deck. At the beginning of 2001, the Granollers Borough Council commissioned Alfa Polaris to carry out the concept design and the detailing document of a new link between these two urban areas.

The design of the proposed link, a footbridge over the mentioned road, was strongly conditioned by the asymmetric shape of the cross-section of the road trench, and by the bad ground conditions on the top of the south slope. We looked for a design that highlighted this asymmetry marked by the different level of the two banks and the presence of a small platform in the middle of the south slope of the trench.

We also looked for a solution with reduced whole life cost and environmental burdens.

This is the reason why we chose Corten steel —whose rusted skin protects itself from further corrosion— for the structure, LED lamps —with long lifespan and energy efficiency— for the street lighting over the deck, and polymeric timber —with almost no maintenance— for the decking over the structure.

The structure we proposed is formed by the main deck composed by a cranked shape continuous steel beam, with two supports, one at each side of the road, and a secondary deck.

The latter is a simply supported structure that spans 13.9 metres, from the top angle of the former to the free end of its cantilevered span. The primary deck has a main span of 32.7 metres and a cantilevered side span of 5.0 metres. It is formed by two longitudinal hollow box girders, and on its top angle it has the maximum width and depth, which decrease in both senses, being minimum at the free end of the cantilevered span, and over the north abutment.

Along the main span, the footpath is channelled by those two box girders, which are linked together at bottom flanges by transversal beams. The latter, in turn, give support to the two metre wide polymeric timber decking. Below the secondary deck, the two girders that form the main beam are linked together through transversal diaphragms hidden by external plates, so that the beam seems to be a single box girder.

The scheme also included the upgrading of the south approach, with the widening of the sidewalks and the construction of raised crosswalks to provide pedestrians a safe access from that side. On the north bank, a small ramp around the abutment was constructed.

On the deck the street lighting is provided by means of twelve LED lamps, supported and protected from vandalism by means of Corten steel shelters fixed to the inner webs of the main girders. Additional lamp columns, with stainless steel stems, were installed on both approaches.

The construction started in June 2009 and the footbridge was open to the public in January 2010.

Contributed by Xavier Font-Alfa Polaris

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