STEDELIJK MUSEUM OF MODERN ART
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would be fixed to its supporting steel structure. Using data from the Dutch building codes on wind loading and temperature ranges, Solico could then use this model to simulate how particular composite materials would withstand the various stresses and strains of high winds, high summer temperatures and freezing winter frosts. To really make certain of the wind-loading data, a physical model of part of the façade was built – including the static mounting points – for testing in a wind tunnel. For the wind testing, Solico only tolerated a deformation level of up to 0.3 percent of a panel’s total dimensions. And its tolerance for thermal expansion was even lower. Even on a hot summer’s day, the panels could only expand by 0.1 percent of their total length. According to the building codes, the range of temperatures that the facade will be exposed to ranges from -25 degrees Centigrade to +35 degrees Centigrade. Glass and metal were ruled out, due to their thermal expansion properties. The only option was composites. And fibreglass was not suitable, as its thermal expansion was still too high. Solico’s feasibility study showed that the optimal solution to meet all requirements was a composite sandwich construction. In this construction, the outer skins consist of composite laminates, reinforced with carbon and aramid fibres. The basic principle is that, whereas the resin expands as the temperature rises, both Twaron aramid and Tenax carbon fibres actually contract, due to their negative longitudinal thermal expansion coefficient. The result is a composite with a minimal thermal expansion. Teijin Aramid’s fibre research laboratory measured its thermal expansion on actual samples of the proposed composite. The experiments were in line with the calculations made by Solico and confirmed that the Twaron-and- Tenax-reinforced composite identified by Solico could indeed turn the architect’s vision into reality.
PRODUCTION OF THE COMPOSITE PANELS With feasibility established, the next challenge was to work out how to actually produce the 185 enormous composite panels that would be needed to make the façade itself. Holland Composites, a pioneer of the use of composites in the architectural sector, were enlisted. The first step was to find out whether the sandwich construction would perform as well in real life as it had in Solico’s feasibility study. So Holland Composites constructed a prototype – a set of six panels, bound together, sanded and coated just as if they formed an actual part of the façade. Using this test panel, Holland Composites and Solico were able to confirm that the Twaron-reinforced composite could enable a flat, smooth appearance. Combined with its minimal degree of thermal expansion, which gave the composite material the green light, this meant that Holland Composites could begin construction.
Although the largest panel would be 15m high and 3.5m wide, it wasn’t their size that caused the biggest challenge during production. It was the fact that they had to be perfectly flat. Composites can be molded in virtually any shape. And curves are easy, because humans can’t spot small differences in angle or direction in a curved surface. However, we are very good at detecting the slightest deviation in a flat surface – especially when the surface is glossy.
Holland Composites had to design a huge table that they could use as the base for injection molding the laminates for the composite panels. The first step was to lay down the unidirectional fabrics of Twaron para-aramid and Tenax carbon fiber on top of a film on the surface of the giant table. Next, a layer of PIR foam is put in place, and the sandwich is completed with a second set of layers of Twaron and Tenax fabrics. Plastic film is then wrapped around the sandwich to make the mould
The smooth curving lines of the ‘bath-tub’ extension are a pointedly stark contrast to the Neo-Renaissance style of the original building.
30 | Architects Choice |
ArchitectNews.co.uk
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