Westfield Mall of the Netherlands, Leidschendam | Total concept for construction and aesthetics

Westfield Mall of the Netherlands is a 'monument to the future'

'One gesture, one design, one identity' exudes Westfield Mall of the Netherlands, in the words of architect Roberto Meyer (MVSA). The cladding plays a dominant role in this, with the eye-catching prefabricated concrete 'voile façade' embracing the mall like a silk scarf, according to the designers. A structural-aesthetic and logistical challenge for facade contractor TGM-NL B.V. and suppliers, such as specialist in pre-cast concrete mbX. The co-makers speaking.

"We advised on behalf of Unibail-Rodamco-Westfield on the overall facade scope prior to the tender," begins Commercial Director Leon van Osch. "Our tender documents were adopted one-to-one by main contractor Ballast Nedam at URW's request. In addition to the 'voile façade' and ceilings, these include all the facade parts, such as the secondary steel structure from which the voile hangs, the HSB elements and the curtain walls in steel and aluminum. Also included in our scope are the natural stone facade parts and the green facades." Westfield Mall of the Netherlands is a customized assignment for TGM on all fronts - design, logistics and execution. Here, the white voile façade, an apparently draped facade finish that blends seamlessly into the canopies, is the eye-catcher of this "almost un-Dutch" structure. To demonstrate its manufacturability and aesthetic quality, a fully representative mock-up measuring 12 x 20 meters was built immediately after the tender phase.

Parametric modeling
"We have made double-curved concrete our own niche," says director Bjorn van Overveld of mbX (winner of the European Concrete Prize with Arnhem Centraal). "What we produce is never 'standard,' and so for this project we set up our own production line. For 'The Mall,' different production methods are used with regard to the shell elements. By converting the 3D design to a parametric model, it was possible to determine the most efficient production method. This includes all available data and relationships." Part of the production method is the flexible molding technique, which can be used to create unique formwork parts. "Partly because of this, we have the ability to create freedom of form in production. There are certainly repetitive parts, but much of the production consists of unique elements. Without the current state of digital technology, this design would not have been feasible." 

Assembly
All the elements for the voile façade and canopies (approximately 9,300 m²) were further developed by TGM and mbX into a virtual technically feasible 3D model based on MVSA's aesthetic design. During the elaboration of this model, both the concrete elements and the related secondary steel structure are coordinated three-dimensionally. "The produced concrete elements are assembled as much as possible into larger modules by providing them with transport and suspension structures at mbX on site," says Frank van den Heuvel, project manager of TGM-NL B.V. "Then they go on transport. Of course, the assembly methods also differ greatly due to the diversity of the facade elements, accessibility and safety. The logistical complexity is caused, for example, by the streetcar track in use, which sometimes requires work at night, as well as the fact that the existing shopping center remains in use. Simultaneously with the assembly of the secondary steel structure and the concrete voile, the thermal shell and the profiled metal facades are also being assembled. Assembly will continue into 2020."

Pleats
The concrete modules are assembled with hoists, elevating platforms and lifting tables, as at the location of the twelve-meter cantilevered canopy section at the main entrance. The horizontal folds between the undulating shells incorporate a standard joint of nominally twenty millimeters. This is designed to minimize contamination of the concrete by rainwater. The folds themselves are inverted 'potted', allowing the rainwater to be drained along the back. Van Overveld: "The angles of those folds are determined in such a way that the facade appearance is not disturbed by the joints, a process that is closely monitored." 

One movement
All façade components connect to the voile façade and as a whole form the thermal shell. Van Osch: "It is also worth mentioning that the profiles of the steel curtain walls are laser-welded for optimal results, again for aesthetic as well as structural reasons. After all, large spans are involved." The logistics side of the mall will feature green facades, making Westfield Mall of the Netherlands an all-sided building in all its uniqueness, dominated by the inviting voile façade. "You will soon see one movement of a voile fabric on the facade, here slightly narrower, then imposing again as at the main entrance, with a height difference of up to twenty meters. With our total facade concept as co-makers, we ensure that the end result is as intended: one gesture, one design, one identity. As far as we are concerned, a monument for the future," Van Osch concludes.