OTH has strived for an architecture by making as little architecture. A seamless combination of industrial heritage and high-tech/innovative technology.

Kraanspoor (translated as crane way) is a light-weight transparent office building of three floors built on top of a concrete crane way on the grounds of the former NDSM (Nederlandsche Dok en Scheepsbouw Maatschappij) shipyard, a relic of Amsterdam’s shipping industry. This industrial monument, built in 1950 by architect J.D. postma, has a length of 270 meters, a height of 13,5 meters and a width of 8,7 meters, a street length and width, and was saved from demolition in 1997. The new construction assembled on top of this old concrete base – the original Kraanspoor – is the same 270 meters long, with a width of 13,8 meters, accentuates the length of Kraanspoor and the phenomenal expansive view of the river IJ and the old city–centre of Amsterdam. Fully respecting its foundation, the building is lifted by slender steel columns 3 meters above the crane way, appearing to float above the impressive concrete colossus.

The challenge of the design for OTH was to realize a maximum surface area without having to make radical adjustments to the existing concrete structure, utilizing its maximum allowable load-carrying capacity. To help minimize the weight, a light-weight building of steel structure in combination with an infra+ floor system (now referred to as Slimline-floor concept) was chosen for the new development, reducing the total building weight nearly by half.

The existing concrete crane way functions as a foundation for the new building, and carries the maximum possible weight of a three storey building, with an asymmetrical overhang (of 3,25m) on the water-side. This is due to the foundation’s heavier load carrying function for the former revolving cranes used in ship assembly that cantilevered to this side.

The Infra+ floor is supported by integrated steel beams spaced on centres of 7,67 meters with a span of 8 meters. Over the infra+ floor lies a (weight saving) wooden panels running surface. Tucked away in the hollow space above the concrete skin ceiling and below the top floor are the installations, allowing for a maximum clear height.

Using fishplates in the support of the infra+ floor beams on trusses creates a continuous floor and hence substantial stiffness. The stability of the building on the crane way is due to the steel K-bracing structures.

The newly built construction is characterized by its transparent double-skin climate façade of glass. The vast surface of glass supplies ample natural light to its interior, promoting a pleasant work environment. The inner façade boasts hinged timber windows (that can open) with a full height from office floor to ceiling, the outer façade consists of motorized glass louvers (sun sides printed with a dot pattern to keep out the sun and the light reflected off the water) that can be opened per segment horizontally to 90°, forming a lively and variable façade . This climate façade allows for ventilation of the offices by low energy mechanic suction via the floor system and acts as a buffer against heat in the summer and cold in the winter. The Infra+ system with a concrete ceiling layer of only 70mm has pipes cast in for concrete core activity. The water from the IJ river is pumped up and used for hydrothermal heating as well as cooling. (Supplement heating is possible through use of a gas boiler.)

The four double portal frames of the existing concrete structure function once again as stairwells. A separate prefabricated steel structure was specifically developed and includes new stairs and a panorama lift. This one piece pre-assembled construction was hoisted in its entirety with utmost precision between the double concrete portal frames and attached to the foundation for additional stability.

The two gangways alongside the entire waterside concrete crane way function as fire-escape routes. In the heart of the original concrete structure, underneath the new structure, is housed extensive archive/storage space, as well as the technical building services.

Kraanspoor has been realised with the utmost respect for its history as well as its natural surroundings. The site was formerly choice nesting grounds for water birds, thus Kraanspoor is equipped with nesting houses to maintain the biodiversity in this area.

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