Multi-storey car parks made of steel

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 parks 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 m x 2.5 m parking spaces alongside a 6 m 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 latter is a factor that improves users' 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 car park 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 (1947-1962), 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, or 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 m to 16 m in length. However, if the 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 14 m; this layout offers greater ease of parking and vehicle flow within the car park, but it requires a larger parking space surface area than the 'comb' type. The minimum height of each floor is generally 2.1 m 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.

Text: Tommaso Tirelli
Photos: ArcelorMittal Europe - Long Products, Azéma Architectes