Home > Magazine > Issues > #42 Nov/Dec 2011 > Observation tower, Peize

Observation tower, Peize

Observation tower

PEIZE (NL) - UNStudio explores the possibilities of ultra high performance fibre reinforced concrete in a 25-metre-high observation tower.

Ultra High Performance Fibre Reinforced Concrete (UHPFRC) is an innovative material that has so far been used on a limited scale in, among others, bridge projects in Germany and France. In the Netherlands, because of its higher cost and the absence of specific regulations, there has been a reluctance to use the new material. To overcome that hesitation, three case studies aimed at showcasing UHPFRC's possibilities were initiated by the cement industry's top body, Cement&BetonCentrum. Two of the three studies concern projects for Natuurmonumenten (Dutch Society for the Preservation of Natural Heritage), which was presented with the designs upon completion of the case studies and now must find the means to realize the projects.

Last year a case study was carried out for a very slender, fragile-looking pedestrian bridge designed by Maurice Nio, and this year a team made up of UNStudio, structural engineers ABT, construction company BAM Utiliteitsbouw and Haitsma Beton produced a design for an alarmingly canted observation tower. UNStudio's Ben van Berkel has always been fascinated by dynamic equilibrium – see, for example, his first signature structure, the Erasmus Bridge in Rotterdam – and ultra high performance concrete is an ideal material in which to indulge that fascination. It differs from ordinary concrete in that it contains steel fibres and has a very high density and an extremely fine-grained structure. These properties enable it to withstand large compressive stresses in structures of narrow dimensions.

The lookout tower is a hybrid steel and concrete construction. Steel is employed where tensile stresses predominate, and ultra high performance concrete where the compressive stresses are highest. The parapet around the stairs and platforms is made from stainless steel mesh, which offers both transparency and the required safety.

If Natuurmonumenten manages to find the necessary financial support, the 25-metre-high lookout will be built on the forested boundary of the Onlanden nature reserve, where it will extend five metres above the tree tops. Visitors who make the effort to climb the 134 steps to the top (and don't suffer from vertigo) will be able to look out over the 3000-hectare nature reserve, which is also the largest water storage area in the Netherlands and is used as a water management buffer for the country's north.

Visitors are led fluidly to the top in three stages. The first ends in a viewing platform at a height of ten metres, after which a second flight of steps provides a change of direction and an alternative view as it leads visitors through the tree canopy to the second, 20-metre-high platform, from where there are treetop views over the nature reserve around the city of Groningen. Those who climb the third and final flight of steps to the highest platform (at 24 metres) are rewarded with an unimpeded, panoramic view of the reserve and a brief escape from the flat Dutch landscape.