Les Machines multi-storey car park in Nantes with ArcelorMittal steel structure

Detailed information

Location & architectural concept

Nantes, the Loire, its shipyards...The site is indelibly branded by its history of shipbuilding: abandoned, stripped out, derelict saw-tooth roofs, large-span portals, cranes, graving docks, shipyard buildings, slipways - yet a narrative, a heritage, a record of the past is imprinted here. They endure and affirm the area’s identity.

So the city moves on, cities change, but here the city on the Loire River bears testament to a rich heritage and a proud industrial history. The vestigial remains cannot be erased. Today the city is no longer trying to erase the past but to make the most of what has survived.

Building a multi-storey car park with this burden of the past and the evidence of a city’s dynamic energy requires that a point of balance, or even of convergence, be found so that this heritage advances into a new era.

The multi-storey car park project is located on the Ile de Nantes, on the 'Prairie au Duc' site in the midst of the former shipyards. At the heart of the Alstom site - where two halls are still operating - the car park takes the place of two abandoned halls. It faces 'La Grande Nef,' a renovated shipbuilding hall.

The car park: Structural design & fire safety considerations

This 1000-space car park comprises seven half-levels. The building is 110 m long x 30 m wide, with a total height of 22 m. This structure is completely open on 3 sides - only the longitudinal facade adjoining the existing hall is protected by a fire wall.

Built on the tip of the island in a wind-exposed area, the fire service classified it as an open-sided multi-storey car park. They consented to this type of construction subject to a real fire study in accordance with the Eurocode.

In order to comply with the decree relating to open-sided multi-storey car parks, a break was created in the middle of the structure, so that the distance between opposite facades open to the air is 70 metres. The purpose is to ensure smoke clearance during fire simulations. The maximum facade to facade distances for the public in the event of fire have been met. The break zone is equipped with floor gratings accessible to vehicles within the traffic lane.

The scenarios proposed for the study are conventional, and in accordance with the standards applicable to this type of structure.

The car park’s primary structure is a composite column-beam frame with a 16 m span comprising rolled H-sections stabilised by a wind-bracing system (also consisting of H-sections) and incorporating structural floor decks connected to the steel structure.

It has a 5.2 m grid, with joists every 2.6 m. The floor consists of Cofraplus® 60 composite floor deck with beams and joists of rolled IPE sections (IPE 400 in grade S355). The columns are rolled HEA sections without cladding. Fire protection is provided by intumescent paint. The wind bracing structure and vehicle stop bollards also consist of HEA sections and are anchored to the edge beams.

The beams in the central row were oversized to take account of the parking of cars in adjacent rows.

To limit the spread of fire from level to level, the C+D dimension is 80 cm at the periphery of the building. The project was submitted to the Approval Bureau recognised by the Ministry of the Interior and authorised subject to the following comments: "Install a firewall on the centre row on every half-level to limit vertical fire propagation. (Two half-levels constitute one level)”.

Reminiscent of a shipyard, governed by geometry

The design is reminiscent of the shipyards where a structure encased the ships to enable their construction and when the ship was launched, only the framework remained.

This metal structure derives all its impact from its great length, the repetition of identical steel elements, and its alignment to the street and the boulevard.

The project’s impact is enhanced by its open and unconfined character. The safe and pleasant pedestrian routes are protected from the cars with walkways along the facades. The pedestrian is drawn by passageways towards the light and the views and perspectives across the city. The movement of pedestrians will give this functional building a dramatic dimension through their mere presence, the movements of visitors, and the speed of the cars whose headlights at night will bring life to the structure.