Steel 'specials' allow cantilevers of more than 10 meters

For example, because of the special cantilevered living rooms on the upper floors, which are unique in shape, size and complexity. The steel structures of the so-called 'specials' were engineered and produced by Oostingh, part of the ASK Romein group of companies, which is also responsible for the steel structures of the penthouses and rooftop skybar.

Valley Amsterdam includes the construction of three rectangular (residential) towers with heights of 103, 80 and 70 meters, respectively, and space for 200 homes. The towers will be built on a seven-story plinth building with offices, culture, retail and hospitality, as well as a three-story parking basement. "At the base of the (residential) towers are three concrete cores," says Kees Oudshoorn, Manager of Engineering at Oostingh. "The unique design of the building is mainly realized in precast concrete. However, for the large cantilevers of up to 10 meters, precast was not an option. Instead, high-quality steel structures were chosen."

'Tolerances were extremely tight'

Bouwcombinatie Valley Amsterdam (Boele & van Eesteren | G&S Bouw) commissioned Oostingh to engineer and produce seven cantilevered 'specials' in late 2018. "In close cooperation with our client and structural engineer Van Rossum Raadgevende Ingenieurs b.v., we provided the engineering of the steel specials in about a year and a half," Oudshoorn said. "The specials were suspended from the prefab structure like boxes; a process that took a lot of work. For example, we had to deal with complex and heavy steel-concrete connections. Already during the pouring of the concrete cores, large plates with anchors had to be inserted to the millimeter. So the tolerances were extremely tight. For this project we had to make quite complex calculations, a butt of ours."

Just-in-time and in one piece

During Valley's construction, work is done according to a lean schedule, which shows all sub-milestones. "Moreover, due to the limited site space, all materials are delivered in lean order and processed immediately," Oudshoorn said. "After production, our specials were transported on demand from our Katwijk factory to Amsterdam and assembled, including associated steel plate concrete floors. The structures were then lifted as one unit to the appropriate floor and suspended, to a height of no less than 90 meters!"

Acoustically decoupled

Penthouses were built on the upper floors of Valley, for which Oostingh also supplied the steel structures. "Also special is the rooftop skybar overlooking Amsterdam," says Oudshoorn. "Various activities will soon be organized in this skybar, from which residents must not experience noise pollution. Therefore, the construction of the skybar had to be acoustically decoupled from the precast concrete core, and this both horizontally and vertically. To make this possible, the steel structure was designed as a sort of donut around the concrete core. The "floating" structure is connected to the concrete core using thick rubber trestles. To keep the steel structure stable during assembly, we made temporary stability devices. Quite a challenge at a height of 100 meters, in which we succeeded excellently!"