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City Hall Utrecht: a light structural system based on functional diagonals
Built partly over the Central Station, the iconic new City Hall in the Dutch town of Utrecht was conceived as a vertical landscape. Unique is not only its shape, but also its structural design that resulted from its complex location. ArcelorMittal supplied steel sections in Histar® grade and composite flooring deck for the building's structure.
The new Utrecht city hall, designed by Kraaijvanger Architects, stands at a promising yet extremely complex location, namely partly beside and partly on top of the new station concourse developed by Benthem Crouwel Architects. Making both the station concourse and the municipal offices accessible from the plateau above the railway tracks and platforms formed one of the challenges. The complexity of this design assignment was increased by the planned transport hub for bus and express tram connections at ground level.
The lower three levels of the city hall, located between ground level and public level, are used for parking and for technical facilities. Together, they form a podium at public level at approximately 7.5 metres above ground level, linking up with the station concourse above the railway tracks and platforms. Particular attention was devoted to connecting the area on both sides of the tracks by means of a ‘central boulevard,’ which hangs above the tracks alongside the new station concourse and opens up on the western side into the area in which the city hall and the station concourse meet. The building's entrance hall is located in this central boulevard.
From the public plateau, the first few levels are intended for public functions. Three floors (6, 11, and 21) serve as meeting places (plazas) and are characterized by their higher ceilings. The other levels house office space.
The shape of the building is determined by a combination of three types of buildings: the public foyer divided between the first five floors, the surrounding, rectangular building element that crosses above the station's roof, and the divided towers. In terms of construction, the layout is based on relatively few supports with large-scale forces instead of the usual even distribution. Due to the great depth of the building, larger empty spaces have been created in various places by means of atriums and inner courtyards in a semi outdoor climate, for optimum daylight access and a pleasant work environment.
The architects wanted to prevent the city hall becoming an icon of bureaucracy, even if only due to its size. It was therefore important that the working areas and the public foyer had a visual relationship with each other, and that the building opened itself up to the public. This communicates the literal transparency of local government and creates an inspiring, open building. The relatively small footprint of the building meant that not all public functions could be housed on the same floor. Instead, they are divided over several levels around a large, spacious atrium. In this regard, it is important that these floors are not situated directly above one another but instead are staggered and stick out. This creates multiple lines of sight and views. From the entrance hall, there is a view of a subtropical inner garden on the first floor and a four-storey-tall window.
The stacking of three types of building and the varied daylight cut-aways produce different results on every floor. These sections connect the floors with each other to form a vertical landscape In this way, different functional possibilities are created per floor, the visibility of and for the public is increased, and the scale of the building is kept modest. The public foyer, the outdoor space, the daylight zones, and the working areas are all spatially connected within the compact layout.
Structural design & ArcelorMittal steel
Due to its complex location the city hall required a special structural design. The construction - which follows the periphery - is visible in the building's façade. It doesn't follow a purely right-angled system, but a system of fully functional diagonals which transfer the vertical loads in the façade. Together with the north tower's concrete cores, these diagonal elements also provide stability to the building.
The south tower, built right over the Central Station, is supported by only five mega columns that cut through the Public Transportation Terminal. A complex 3D structure transfers the loads from the south tower to the columns.
ArcelorMittal Europe – Long Products supplied around 8.000 tn steel sections, 5.000 of which were HD sections in Histar 460 grade, used as columns in the City Hall's structure. Furthermore, ArcelorMittal Construction's composite steel deck was used in the project to constribute to the weight reduction of the structure.
- 2009 - 2014
City of Utrecht
- Engineering Firm:
- Steel fabricator:
ASK Romein - Oostingh Staalbouw
Boele Van Eesteren, G&S Bouw
© Stijn Poelstra & Kraaijvanger