The Wilhelminahof was the first project to be completed on the Kop van Zuid, in an ambitious urban development operation to connect this part of Rotterdam-Zuid with the city centre. The complex consists of a court of justice with accompanying offices, a building for the tax office, an office tower and carparks. The start of the design process was in the form of a workshop facilitated by the then Chief Government Architect, Kees Rijnboutt. The Wilhelminaplein metro station is situated beneath the complex.
In the initial stages of the project a canopy was designed to function as a pedestrian route protected from the elements between the various buildings and the metro station. The canopy forms the heart of the complex of buildings, a central entrance area for the four surrounding buildings, and also functions as an eye-catching feature from afar.
The roof of the Galleria is a pleated glass membrane. A consistent gutter level was established in order to connect it to the surrounding buildings. The space between the buildings is differentiated and accentuated by varying the height of the roof. The metro entrance and the main entrance to the Galleria stand beneath the highest point of the glass roof.
The glass canopy is supported by a steel structure with tree-like columns. The tree form was derived from purely structural principles: as few columns as possible on the ground and myriad support points beneath the glass membrane of the roof. The horizontal stability is drawn from the surrounding buildings, so the construction could be very slender in design. The Â‘trunkÂ’ of the tree is made of sturdy steel plate, while the Â‘branchesÂ’ are made of rectangular and round tubing. The treeÂ’s form and size depends on the glass surface that requires support. The roof membrane was designed first, and then the exact form of the tree-like load-bearing structure.
In the draft design, every branch of the structural trees ends in a junction where four, six or eight reinforced glass plates meet. The glass panels can be joined without a frame, connected with nothing more than a seam of sealant. A specially developed glass joint makes it possible to construct a glass membrane with a double-curved shape using flat triangular and quadrangular sheets of glass. Then, in order to avoid the vulnerable sharp points of triangles and reduce wastage from cutting the glass, a way in which to use only quadrangular plates in the intricately shaped canopy was sought. The use of glass sheets in the form of rectangles and parallelograms, which are no more than two conjoined triangles, proved to barely inhibit the free-form design and was a much more efficient way of using materials.
If the roof had been realized then the Galleria would have been visible from the centre on the northern banks of the Maas. In the evening, the multifaceted canopy, lit from below, would have sparkled like a diamond on the southern banks of the Maas.