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Extension of the Geric Shopping Centre and construction of a car park with optimised ArcelorMittal steel solutions
Thanks to the use of steel and innovative construction techniques, the extension of the Geric Shopping Centre in the French town of Thionville was realised in less than 10 months. The importance of the project lies in the global optimisation of the structural system and the architecture and in the innovative fire engineering approach for both car park and shopping spaces. ArcelorMittal's Angelina® beams, ACB® beams, and Cofraplus® 60 composite flooring deck were used.
An complex extension project
Faced with the impossibility of increasing the size of the property, the decision to extend the Geric Shopping Centre in Thionville called for an unconventional solution. Therefore, the planned new building had to be erected on the site of the centre's outdoor parking area situated south of the existing building. Apart from increasing the commercial area, the extension thus also had to include a car park offering at least the same number of client parking spaces as before the extension.
Furthermore, the interruption of the shopping centre's commercial activities had to be kept to a minimum in order to reduce losses for the shops and businesses.
Given all of these circumstances, the only feasible solution was the use of steel for the structure of the new building due to the speed of construction the material guarantees, among other reasons. The new building could be completed in a record time of just 10 months, from February to November 2013. A realisation in concrete would have interrupted the commercial activities for at least 18 months. Thanks to the fast construction, the centre's businesses didn't miss out on the end of year sales of both 2012 and 2013.
Covering around 5000 m2, the new south wing of the Geric Shopping Centre offers four levels. New shops and commercial spaces were created on the ground floor and an open, ventilated car park was built on the three levels above, increasing thus the number of parking spaces compared to the situation prior to the extension.
It was the owners', architect's, and engineering office's main aim to optimise the structural system in all possible aspects. Steel and composite elements were chosen as structural elements as they contribute to the structure's weight reduction, cost efficiency, and construction speed – all considered key factors in the Geric project.
The structure comprises four levels with a dimension of approximately 70 m x 70m. On the ground level, the commercial spaces, ArcelorMittal's Angelina® beams were used as floor beams as their large openings provide aesthetics and transparency and can incorporate technical installations.
The flooring structure on the three car park levels is composed of ArcelorMittal Cellular beams (ACB®), on one hand for the optimisation of the structural system, but also for architectural reasons. The ACB® beams' circular web openings suggest higher floor heights as the human brain only perceives the upper part of the beam which gives the impression of openness and increased safety.
ArcelorMittal Construction's composite flooring deck Cofraplus® 60 was used for the floor slabs on all levels. Thanks to its easy installation and light weight, Cofraplus® 60 contributes to the structure's efficiency and therefore helps to reduce its environmental impact.
As the steel structure would remain visible on all levels and mainly unprotected against fire, it was galvanised entirely in order to ensure durability.
Innovative fire engineering approach
The construction techniques used for this project applied the latest innovations in terms of structural calculation and fire engineering.
The structure of the commercial area was the first use of Angelina® beams calculated with partial protection taking into account the membrane action of composite structures in case of fire, and the car park was the first one in France built using unprotected ACB® beams.
The project design followed the French procedure for the calculation of unprotected car park structures, taking into account the three usual French fire scenarios:
- 4 cars around a central column
- 7 cars in line at the corner of the car park
- 1 car in the circulation area
The innovation lies in the structural calculation of the cellular beams using the models developed by the Research Fund for Coal and Steel (RFCS) project, FICEB+ (Fire Resistance of Long Span Cellular Beams Made of Hot Rolled Profiles). In the past, it was not possible to perform such calculations taking into account the specific features of cellular beams.
For the commercial area, the new calculation technique taking into account the membrane action of partially protected composite slab in case of fire was used for the first time on the French market. This calculation technique is based on various research projects and has been implemented into the user-friendly software MACS+. It allows for savings of about 50% of the fire protection by applying it only where it is really necessary.
ArcelorMittal played a leading role in various research & development projects without which this new approach wouldn't have been possible. Among them worth mentioning are: Fire in Car Parks, Fire Resistance Assessments of Partially Protected Composite Floors (FRACOF), RFCS Fire Resistance of Long Span Cellular Beams Made of Hot Rolled Profiles (FICEB+), and RFCS Membrane Action of Composite Structures in Case of Fire (MACS+).
The global optimisation of the structural system and architecture in combination with this state-of-the-art fire engineering approach makes the Geric Shopping Centre extension project an important reference for open car parks and shopping centres.
Riger Lepage - Ertim, Paris
- Engineering firm:
Yannick Labart, BET Huguet
- Steel construction:
Gilles Martin, Oh Dancy, Olivier Vassart