Amsterdam: residential tower in wood hybrid construction
Only one has more storeys
The HAUT residential tower in Amsterdam sets new standards in building with wood. This is because the load-bearing structure of the 73-metre-high building consists of concrete and large amounts of timber. With its 21 storeys, it is one of the tallest buildings of its kind. In this context, the timber hybrid construction method combines both ecological and economic advantages. Wood elements, timber-concrete-composite (TCC) panels as well as steel and concrete components were among the elements used. Hybrid construction specialist Brüninghoff from Heiden in the Münsterland region was engaged by the main contractor J.P. van Eesteren B.V. to manufacture and assemble a wide range of prefabricated components for the building project. The shape of the building, the construction method and height presented the planning team with unique challenges. Examples include the prevailing wind loads and the settlement behaviour of the materials. The use of Building Information Modeling (BIM) contributed to improved communication between the project participants and encouraged transparent collaboration.
Alongside the Amstel River in Amsterdam, one of the world's tallest wooden buildings – the HAUT – has been erected over the past few months. The residential tower has 21 floors and is 73 meters high. Inside the building, on a gross floor area of around 14,500 square metres, are 50 modern residential units with spacious terraces and balconies and a spectacular view of the surrounding area. When the high-rise building was designed, those responsible opted for a hybrid construction method that combines concrete with a significant amount of timber. Due to its capacity to store carbon dioxide, the material proves to be ideal for meeting the high ecological demands of the project and its sustainability concept. In this context, the building was certified with the BREEAM Outstanding label.
Hybrid construction expertise
The residential tower was commissioned by Lingotto back in 2016 – the company is both client and project developer. The building has now been realised according to plans by the Dutch architectural firm Team V Architectuur in cooperation with Arup Netherlands. The general contractor is J.P. van Eesteren B.V. in Gouda. As part of the planning and consulting team, Brüninghoff was also involved in the lighthouse project on the Amstel River. In particular, the Münsterland-based project construction specialist contributed its expertise in the field of hybrid construction. The company also handled the timber joining as well as the manufacture and assembly of the wood elements, the steel and precast concrete components, and the TCC ceilings for the construction project and therefore spent a total of eleven months on the construction site in Amsterdam. Overall, the construction time of the project was three years. During the planning phase, the following were involved in an advisory capacity: the Woschitz Group from Vienna, Assmann Beraten + Planen from Hamburg, Prof. Dipl.-Ing. Rainer Pohlenz from Aachen, Ekoflin from Bavel as well as Brüninghoff. In the construction phase, the planning team for timber construction engineering consisted of Brüninghoff, Assmann Beraten + Planen from Hamburg and RWT plus from Vienna.
Timber and concrete for the load-bearing structure
The building shape of the HAUT is based on a trapezoidal foundation. The structure essentially consists of a staircase core made of cast-in-situ concrete, floors made of a timber-concrete composite and a façade made of non-load-bearing timber frame walls. Wood was also used to a large extent for the load-bearing walls and columns in the building. Steel and concrete edge beams were placed in the area of the cantilevers in the “wedge-shaped” part of the building. Cantilevered steel beams with a precast lightweight concrete element create the balcony structures on the sides of the building. The façade was constructed with non-load-bearing timber frame walls made of spruce and fir wood. The individual elements are planked with a gypsum fibre board on the inside and a fibre cement board on the outside. Insulation material fills the interior of the elements. As a whole, the building design allows for a high degree of flexibility in terms of room layout and potential ways of using the building.
Hybrid ceiling elements
The use of timber-concrete composite systems provided an ecological and at the same time economical solution for the ceiling area. These hybrid elements combine the advantages and characteristics of both building materials in one system. With their sound insulation, fire protection and static properties, these can also be used in multi-storey buildings as an alternative to pure concrete ceilings. The standard floor element in the HAUT consists of a 160-millimetre-thick cross-laminated timber panel (CLT) and 80-millimetre-thick concrete of grade C55/67. The largest elements are up to 5.90 by 3.05 metres in size; the smallest element is triangular and measures 1.50 by 1.50 metres. Spruce cross-laminated timber, supplied by Mayr-Melnhof from Gaishorn am See in Austria, was utilised for the construction of the ceilings. Since the underside of the timber-concrete-composite ceilings remains visible, the apartments are characterised by a natural wood appearance. In addition, the natural building material also has a positive influence on the indoor climate of the apartments.
Final steps on the construction site
The TCC ceiling elements were manufactured off-site. On the construction site, the individual elements were then joined. Among other things, this included joint bolting and reinforcement, joint pouring and sealing. Concrete reinforcement bars in the joints connected the individual TCC elements. The joints of the elements subsequently were in-situ-cast. Furthermore, the connection to adjacent structural elements such as walls, columns and beams was established. “The connection of the floor elements to the heavily reinforced staircase was made using steel angles which were dowelled to the structure. The timber-concrete-composite ceiling was suspended from these brackets accordingly”, explains Nils Drachsel, site manager at Brüninghoff. “The very high horizontal forces were transferred using an interlocking system and bolt-in reinforcements.” Except for a special case on the 21st floor, a direct connection of the ceiling slabs to the elevator shaft was not necessary, since the elevator shaft is located in the stairwell.
Storeys – unique and without repetition
“High, complex, hybrid” – that's how Drachsel describes the HAUT's construction. “At first glance, each floor in the building looks the same. But when you look a little closer, you discover that each storey looks a little different. As a result, there are no repetition effects, despite the building´s height.” During the planning process, a variety of challenges emerged – especially in regards to the building's geometry. Due to the building's height, high vertical loads occur, which usually do not arise in conventional timber construction. At the same time, the high wind loads had to be taken into account. Another factor to be considered was the different settlement behaviour of the various building materials: timber, cast-in-situ concrete and precast concrete units. The slender structure of the building had an impact on the building stiffness and building torsion. Additionally, the triangular precast TCC elements required for the trapezoidal floor plan also had to be designed to fit. Key factors in this respect were, among others, the layout of the reinforcement and the load transfer. The load transfer was also an area of concern for the cantilevers. For example, a structurally sound solution had to be found to carry the heavy load of the balconies which were made of a steel bracket, lightweight concrete decking and a fibre concrete façade element and are situated on the outer edges of the structure.
Rapid construction process thanks to a high degree of prefabrication
On the one hand, the renewable resource wood reflects the project´s ecological awareness – on the other hand, the material enabled fast construction progress. The components were produced in Brüninghoff's manufacturing facilities – prefabricated in ideal conditions. The cross-laminated timber was supplied by Mayr-Melnhof. Due to the high degree of prefabrication, the assembly time on the construction site could be significantly reduced. Working with timber, however, also involved some particularities. The fact that the building material had to be well protected from weather influences such as rain on the construction site was one of them.
Challenges in the planning process
Furthermore, efficient communication between the project participants had to be ensured. Challenges in this context included the language barrier, different standardization systems and somewhat different perspectives on the construction process. Coordination among the companies involved also proved to be a challenging task – in addition to Brüninghoff these included Assmann Beraten + Planen as well as RWT plus, two Dutch auditing firms, government agencies and, last but not least the general contractor J.P. van Eesteren B.V. At the same time, it was necessary to organise the many interfaces between the Brüninghoff components and other construction trades such as electrical, plumbing, ventilation, heating, sprinklers, cast-in-place concrete stairwell, exterior walls, façade, balconies.
Transparent communication with BIM
Building Information Modeling (BIM) was particularly helpful for communication. The digital planning method, for instance, made working between the various trades such as building services, exterior walls and the façade much easier. At the same time, it also offered advantages for internal communication at Brüninghoff. Thus, the information exchange between planning, production and construction site ran smoothly. Using the digital building model, those responsible for the project were able to see the current production, planning and construction progress at a glance and plan the next steps and processes. After completion of the building, the BIM model will be handed over as part of the inspection documents.
At HAUT, the natural building material wood was also successfully used at height in a load-bearing function. The overarching know-how, the good cooperation between the project participants as well as the high degree of prefabrication have been contributing factors to the completion of the residential tower in an urban environment with closely timed logistics. As a result, the construction project will serve as a role model for other similar residential construction projects using timber.
Foto credits: Jannes Linders