In total, De Kok Staalbouw produced and assembled 3,882 tonnes of steel in Amsterdam for construction of the Tripolis project. Fire-retardant coating was applied to 32,822 m2 of this steel in-house. The steel structure for the building aptly named Het Venster (‘The Window’) consists largely of steel trusses, PET/THQ beams, finned columns, and walkways, in combination with suspended floors. A remarkable feature is the long trusses (up to 44.5 metres) between the concrete cores and along the temporary facade. Without these elements, the expansion would not have been possible. De Kok Staalbouw is proud of the finned columns, which have aesthetic value in addition to their structural function. A large atrium was created in the middle of Het Venster that serves as a showcase for the existing buildings. To create this atrium De Kok Staalbouw built a high, transparent structure with very slender finned columns that support seven additional floors. Some hanging finned columns were also added to complete the aesthetic picture.
Since part of the project was constructed over the existing building, speed of construction and ease of assembly were priorities. Correct assembly sequence was essential to ensure the stability of the structure so that suspended floors could be installed at a later stage and to make it possible to establish a proper connection to the existing building. In addition to the large quantities of steel, 20,020 m2 of composite metal deck was fitted in Het Venster. The majority of the composite metal deck is located on floors 7 to 12, where approximately 18,800 m2 of steel deck/reinforced concrete floors were fitted to the steel structure. Since the floors of the lower six storeys connect to the existing building, hollow-core slab floors (approx. 1,220 m2) and PET/THQ beams could be used there.
Het Venster was built with a lead time of just 26 weeks. During this same period, De Kok Staalbouw also carried out modifications to the existing buildings, where the steel was mainly used to cover floor openings. A structure for the roof terraces was also installed, which was De Kok Staalbouw's contribution to this project's ‘nature-inclusive building ambition.’