Steel construction of the outer category

With completed projects such as the canopy on the Utrecht Central Station square or the Leidsche Rijn bus station nominated for the National Steel Construction Prize, Buiting Staalbouw is used to some things. Still, the steel builder from Almelo labels the canopy of the inner-city library of the University of Amsterdam as a construction of the outer category. Commissioned by BINX Smartility, Buiting Staalbouw translated the parametrically designed atrium canopy into a manufacturable whole.

"The design of the atrium canopy consists of a steel tree structure that shoots up 20 meters into the air from the basement cum bicycle parking area and then branches out like a canopy toward the existing monumental buildings," said Arthur Heesen, project manager at Buiting Staalbouw. "It results in a particularly complex steel structure with intricate junctions, 600-by-200-mm tubes and intermediate straight bars. In total, there are 55 3D-formed nodes from which 4 tubes each depart in different wind directions. So every detail is unique."

The nodes are complicated on all fronts. "That starts with the engineering process," Heesen explains. "Fortunately, we did manage to model the structural design in Tekla Structures. Based on this, we were able to control production. Then a lot of manual labor was involved to get everything in the right direction. The structural nodes were then covered with huge decorative caps to meet the architect's aesthetically intended picture: nice flowing transitions and rounded shapes. The decorative caps were all shaped by hand based on a few reference points from raw steel plates 1.5 mm thick. In fact, they could not be modeled. Absolute craftsmanship of the highest order. Incidentally, the nodes are made from plates averaging 15 mm thick and the intermediate bars from predominantly 8 mm thick sheet steel."

In the tree structure, Buiting Staalbouw also realized a complex spiral staircase that twists up from the basement. "As if that were not enough, an extremely complex rainwater drainage system has also been integrated, in which 6 curved stainless steel pipes run down from the roof like a vine," Heesen clarified, adding, "I have not built such a complex and unique construction before in my time at Buiting. There are also 2 fairly heavy study platforms hanging from the tree structure and 3 walkways connected to it towards the existing buildings. And on top of the main supporting structure comes another blanket of secondary steel for the purpose of the glass canopy." 

The atrium roof was first completely prebuilt by Buiting Staalbouw in the factory hall in Almelo. "We are now reaping the benefits of that during assembly," notes Heesen. "It all fits very well. The 'tree' has now been installed and welded into place. That alone was quite a job. Welding through sheet steel tubes 20 mm thick is no mean feat, and that too 60 times! Now we are working on the roof, which will be loosely assembled from the scaffolding and connected with temporary bolt connections. After that, the nodes will all be welded off." 

While realizing special steel structures is Buiting Staalbouw's core business, Heesen says this atrium canopy is one of the outer category. "But that too is entrusted to us. We have well-trained engineers with structural knowledge on board. They are very capable of assessing things constructively and proactively thinking along in the constructive but also practical solution. In addition, we are blessed with outright craftsmen in the workshop who are well trained in welding techniques. We are certified up to execution class 4, the highest category in accordance with NEN-EN 1090, and also have the space to build these kinds of enormous constructions 'for'. That makes this project another success."