The biggest rehabilitation project in Paris in 2013 is the transformation of a former warehouse into a modern new mixed use complex. The concrete structure is mainly preserved and slightly adapted, new storeys are added using composite floorings systems of ArcelorMittal's Arval range.

Located in the north-east of Paris along the Boulevard Macdonald, the warehouse with its extension of 616m is the longest building in the French capital. It was designed in the late 1960ies by the architect Marcel Forest for the freight company SNTR Calberson when the deindustrialization of this area started.

As part of a global policy to reduce heavy truck traffic in the city, this warehouse was a centre of reception and distribution of goods at the entrance of Paris.

Apart from its outsized dimensions, the warehouse has another valuable and rare quality: its extension capacities. From the beginning, the building was conceived as a base with a structure that was designed to accommodate additional levels in case this was necessary. Its architecture refects this approach: a monolithic concrete building with a “sober” and repetitive façade, sitting like it if was waiting for future extensions.

The design of the master plan for its rehabilitation, which is part of a larger urban redevelopment in North-East Paris, was awarded to OMA in 2007. It includes the transformation of the existing building and an addition of seven floors that will be dedicated to housing, offices, shops and public facilities.

The existing structure will be largely preserved, it foresees several interior patios and green islands.

Innovative ArcelorMittal steel solutions

Many technical constraint in this large scale rehabilitation project could be solved thanks to the use of ArcelorMittal's flooring systems and technical expertise. In addition to the usual composite floor systems, especially the very light floor system Cofradal 200 with integrated sound insulation and exceptional fire resistance responds well to the requirements of this rehabilitation project. Supported on Slim floor beams (SFB) based on hot rolled sections, the system also creates a very slim slab.

In total, 15.000 m² of Cofradal ® 200, 10.000 m2 Cofraplus ® 77, 13.000 m² Cofraplus ® 60 and around 100 tonnes of finished SFB beams are being supplied between January 2013 and May 2014.

Cofraplus® 220 is an innovative additive steel-concrete floor which combines the high resistance of the patented profile with the reinforced concrete slab. It achieves long spans without propping and permits the design of continuous slabs for heavy live loads of all type of applications: car parks, multi-storey buildings, ...

A a result of an extensive research and test programme, Cofraplus® 220, an innovative concept of steel-concrete floor is born. Its multiple benefits give the designer and architect a new scope for imagination and the client gueranteed economy for large working spans.

Easiness and speed of installation, reduced weight and optimum resistance are the  main features of the new additive floor system which is particularly suited to all column-beam structure projects without intermediary joints.

Cofraplus© 220 becomes an integrated part of all types of girders

WING: floor for steel car parks
COFRAPLUS© 220 sits into the the steel Wings welded at the workshop and positioned in the web of finished beams. Only the concrete on top of the rib of the profile is overhanging the beams. Shear studs are welded on the upper flange of the beams to create a connection between the slab and the girder which leads to important savings in steel weight.

SLIM FLOOR - CoFB: light gauge floor for multi-storey buildings
COFRAPLUS© 220 is positioned into the lower flange of assymentric beams. The rib crown sits into a slim floor connector in order to avoid any seepage of concrete. CoSFB, the composite beam version, is used to connect the slab and the beams and reduces the beam dimensions and the floor depth substancially.

CONCRETE
COFRAPLUS© 220 is positioned into the steel Wings which are precast into concrete beams or on angle brackets anchored into the concrete. The result is a substantial reduction height.

Advantages

• acts as a formwork during concrete pouring

• is acting as a continuous slab (multi span system)

• less amount of rib reinforcement

• les amount or no stirrup reinfocement

• thickness reduction of floor depth between 25 cm and 40 cm (Slim Floor)

• CoSFB (Composite beam) leads to an important cost saving of the girders

The "open front" system guarantees abundant natural ventilation, which is fundamental to safety in the event of fire: records in Europe show that with the advanced structural calculation methods set forth by Eurocodes, it is possible to guarantee structural safety in the event of a fire, thus eliminating or reducing the need for expensive fire safety systems for metal structures.

The concept of multi-storey car parking is often associated with cases of "anti-architectural" design, producing constructions in which the focus is placed on optimising the use of economic resources available in compatibility with safety levels and functional accessibility.

Fortunately, the international panorama offers cases of multi-level parking in which the designer's freedom takes shape and expression in the form of light steel framework as the load-bearing structure along with various other materials in the construction of the outer 'skin'.

The use of steel technologies in multi-storey car park structures is becoming increasingly widespread in Europe, proving an economically advantageous solution which not only reduces manufacturing time, but also allows the car park to be seen as a genuine architectural form rather than considered in its purely functional nature. Given the growing need for car parking in our towns and cities, particularly in connection with public transportation systems and commercial centres, the steel multi-storey car parking solution proves particularly interesting compared with more "traditional" underground parking.

The abundant natural ventilation typical of the construction of these buildings and the specific structural planning to withstand fire conditions allow for safe solutions, even without the use of specific fire protection systems. This is proven by various installations in Europe, whose steel structures have been calculated according to the Natural Fire Safety Concept, as set forth by European safety standards.

Steel structural parking typically consists of 16-metre bays: a section between two pillars made up of 5 x 2.5m parking spaces alongside a 6m track. This solution is highly practical as it allows those parking their cars great manoeuvrability without the obstruction of the pillars. Building "open-plan" above-ground structures comes with the benefit of natural ventilation and light: the former is essential when calculating fire resistance, while the second is a factor that improves the user's comfort and perception of space, while simultaneously reducing the building's energy use.

Moreover, being a "light" material, steel helps reduce the impact of foundations and facilitates construction on sites or areas of limited size (e.g. airports, town centres, railways, etc.). Its prefabricated construction allows for fast installation and, at the end of its useful life, the steel structure may be dismantled and its components reused and recycled. Construction steel is in fact already recycled, with 80% of its production deriving from scrap metal put through an electric furnace. 

The architecture of steel car parks

The car park, considered a construction genre all of its own, dates back around 100 years to the age of the development and diffusion of the automobile. The first garage was built in 1905 in Rue de Ponthieu, Paris, and its external design was similar to those of the adjoining residential homes. In 1940, American Richard Neutra undertook the first multi-storey parking project, for which he selected a steel structure and chose not to incorporate any form of facades into the design so as to reveal the function of the construction. Although the project was never carried out, it did provide a model for others to follow. In his projects for Philadelphia (1947-62), Louis Kahn placed great strategic importance and architectural decorum on above-ground multi-storey car parks.

Today, the decision to make above-ground car parks an urban object with their own aesthetic value is justified for different reasons: those who park in the city centre, or close to an area of interchange with public transport links, airports and hospitals, must be able to park their car without difficulty; the car park must be an easily identifiable object; for shopping centres, " pretty" and functional car parks are an element of appeal for customers and for the diversification of competition.

The distributed layout of a steel multi-storey car park typically consists of a central track 5 or 6 m in length, with parking spaces placed perpendicularly on each side. The open space between the main pillars is generally around 15.5 to 16m in length. However, if the car parking spaces are arranged at an angle to the track (for example 45°), the open space is smaller and the total length of the building may also be limited to 14m; this layout offers greater ease of parking and vehicle flow within the car park, but requires a larger parking space surface area than the 'comb' type. The minimum height of each floor is generally 2.1m to the underside of the beam.

Access ramps can be built in different configurations (spiral or straight, external or internal) while their optimum inclination is between 8% and 10%, and generally does not exceed 12-15%. One solution for reducing ramp length while maintaining optimum inclination is a car park design with a staggered semi-level layout. For all ramp types, the ideal solution is to access each parking deck via a track that is longer coming in (to search for free spaces) and shorter going out and, where possible, to separate incoming and outgoing traffic flows. The pedestrian track must not cross those designed for vehicles. Pedestrian tracks, decks and the division of sectors within the car park are identified by bright colours.