The Tower of Gaia: a complicated steel 'wokkel'

At the geographical center of the municipality of Kerkrade, a very special work of art has risen: the Tower of Gaia. Except for the columns, the entire steel structure is curved and round. It was a challenge for the architect to get it all down on paper, let alone for Visser Staal to make the complicated design feasible. An achievement of stature, which previously led to a nomination for the Construsoft BIM Awards 2022 and now for the National Steel Award 2024.

The 17-meter-high watchtower is an initiative of the municipality of Kerkrade in cooperation with GaiaZOO. Situated in the zoo's parking lot, the tower offers a view of the contours of Kerkrade with all its striking landmarks. Architect Ed Vliegen's design consists of spiral staircases that spiral upward in a wokkel via several landings. Only one route ultimately leads to the viewing platform at a height of 17 meters. As main contractor, Visser Staal took care of the entire project, from translating the architect's design into a 3D BIM model and producing it to on-site conservation and assembly. 

stainless steel fasteners

The unusual arched forms where the spiral staircases are permanently suspended under the structure make the tower extremely complex but architecturally very beautiful, says Christiaan Visser of Visser Staal. "It was therefore quite a challenge to convert the design into a production model." A challenge that did not go unnoticed, given the nomination for the Construsoft BIM Awards 2022 for the most beautiful BIM project in the Benelux. All in all, the structure includes some 50 tons of steel. "We decided to produce everything first and then build it in parts in the workshop. The structure was then disassembled and preserved, and finally reassembled on site. All fastenings were made with stainless steel bolts and nuts in a strength class of 70 to 80, supplied by our regular supplier Kyocera-Senco. We always try to go toward 80. That makes it structurally very strong."

Value Added Services

For Visser Staal, the watchtower is among one of the most challenging works it has ever made. And it is already anything but a "straightforward" construction company. For example, the architectural bicycle bridge in Heerlen, part of the Leisure Lane route through South Limburg, and the equally complex railing on a bicycle bridge in Rosmalen come from Visser Staal. "We are a company that consists mainly of technicians and therefore specializes precisely in such complex works," Visser acknowledges. "And the cooperation with Kyocera-Senco also contributes to that." Besides having a huge stock for just-in-time delivery, Kyocera-Senco also has its own assembly department for so-called Value Added Services. "Sawing work, putting together anchor sets or combining items into one package happens here on the assembly line," says Hendrie Mulleman, Key Account Manager Construction Division at Kyocera-Senco. "And for the Tower of Gaia, Visser Staal made grateful use of that."

In all, the watchtower incorporated just under 2,000 bolts, as well as 80 custom-delivered threaded rods for anchoring with the foundation. "The bolts were all mounted manually and torqued in time so as not to damage the preservation," Visser knows. Assembly was also quite a job, given the unique and complex components. "We spent a total of about three months on site." Although the watchtower is located on the grounds of GaiaZOO, it is freely accessible during the day during the zoo's opening hours. Highly recommended!