Complex steel structures, custom fabricated and assembled

"We processed nearly 3,500 tons of steel in two years," says project manager Luc Vermeijden. "In a project with hardly any repetition and both renovation and new construction, every part was handled and completed integrally."

"This project fits well with our portfolio, which includes the construction of hotel nhow Amsterdam RAI and the most recent renovation of the Johan Cruijff ArenA," Vermeijden continued. Oostingh, part of ASK Romein, focuses on constructively challenging projects in utility construction. From the factory in Katwijk, production is lean. "The advantage of working lean became immediately clear within this project: customized processes with a low error rate and short lead times per project component were quite possible." The structural parts were produced and delivered just-in-time.

The renovation of the south passage of the mall began in 2018, with Fresh! fresh market and a new Jumbo store as major milestones. That project section is the first to be completed, in spring 2019. Westfield Mall of the Netherlands is being realized in densely built-up, urban area. All assembly parts for the main steel structure had to be delivered just-in-time, and assembly activities in public areas took place as much as possible at night, outside store opening hours. Says Vermeijden, "There was construction while the existing shopping center remained operational, so flexibility was a requirement." In other words, the project was characterized by numerous logistical challenges. "Scattered throughout the project were a lot of heavy elements, each requiring special cranes to be erected in a limited area."

All structures were fully engineered in BIM. Heavy, composite and/or double-curved structural elements were involved, sometimes under preload, with spans up to 34 meters and accounting for 18 tons of weight per element. Major specials in the project for Oostingh included the assembly of the truss along the Dining Plaza, 80 meters long and over 6 meters high. The production and assembly of the roof of the Central Plaza, with 30-meter-long, curved flanges of 80-millimeter steel plate under pre-tension, was also complex, Vermeijden said. "The Central Plaza's striking glass roof light, for example, is only a small part of the total roof structure."

The final phase of the project involved the realization of the various entrance awnings. "Engineering, production and assembly were challenging given the double-curved geometry and desired dimensional stability," says Vermeijden, "with a deflection requirement of only a few millimeters despite the span of some 23 meters. Westfield Mall of the Netherlands is 100% bespoke, there is no repetition. Moreover, each building section was accomplished from the drawing board to completion in a very short period of time. There are not many parties in the Netherlands that can do this. Without the dedication and a lot of shifting of the employees it would not have been possible." Except for the canopy opposite the Fletcher Hotel that still needs to be completed, Oostingh's work is complete. "Most of the parts we are assembling will soon be hidden from view, except for a fragment of the arched beams in the roof of the Central Plaza and the standing columns of the cinema entrance. However, I'm sure pride will prevail once the mall is fully completed."