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Super tall, super smart | Vienna CLT tower to be world's tallest

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Every month brings another tower bidding to be the tallest cross laminated timber (CLT) structure in the world. When it is completed in 2018, Vienna’s HoHo tower will take that laurel – for a year or so, anyway. 

Faster, higher, stronger – or just more wooden. For HoHo Vienna the answer is definitely the latter.

The 84m tall, 24-storey CLT tower is under construction over a 4,000marea, within Seestadt Aspern, a lakeside district of Vienna.

HoHo Vienna is one component in a larger project for the area. The entire project is worth €130M (£110M) in total, with €60M (£51M) allocated to the HoHo Vienna site.

“Using wood to build to a height of over 80m is a true challenge in terms of civil engineering and calls for most accurate planning, a creative team and just the right construction site,” says Caroline Palfy, managing director of Cetus Baudevelopment, the development company behind the tower.

“There are hardly any high-rises made mostly of wood. We have taken it on ourselves to pioneer the use of wood in civil engineering, as it were. I have always been a supporter of new, sometimes crazy ideas. That makes it all the more of a pleasure to be able to start with the implementation soon.”

SPQ J5B Holzturm Diagramme Holzvolumen

SPQ J5B Holzturm Diagramme Holzvolumen

This diagram shows the docked CLT construction used on the tower, which shrouds the concrete core. The German caption translates roughly as “docked timberframe”. [Copyright RLP Ruediger Lainer Partner]

Much more than simply “wood”, CLT is used for load-bearing walls, with openings, such as doors or windows incorporated within the panels. The panels are manufactured by placing and gluing layers of timber together. The timber has renewable credentials. and it is claimed the prefabricated components can improve the speed of a construction.

Architects Rüdiger Lainer & Partner ZT, structural engineer Richard Woschitz, Woschitz Group and fire protection engineer Alexander Kunz from Kunz Fire Protection Engineering worked together to combine different construction techniques and materials for the tower.

The system, which is kept deliberately simple, interlocks four prefabricated, serial building elements – supports, joists, ceiling plates and facade components.

The timber composite floors are secured to the building’s supporting core structures and extend out to the facade. The serial elements that make up the timber composite floor structures are supported by timber columns in the outer façade layer. The columns, in turn, form a common mounting element with the likewise prefabricated outer wall, and the façade.

This system means that 75% of the structure from the ground floor up will be made timber.

The tower has a vertically staggered silhouette with an external structure that is meant to evoke bark. Inside, the tower uses exposed timber in ceilings and walls so that residents can be fully conscious of the tower’s timber construction.

The tower’s modular structure can also be adapted to residents’ needs. 

“The use of the space will be tailored to individual needs and can be altered anytime. Subsequent changes can be made at a later stage without requiring any major effort,” says Rüdiger Lainer & Partner owner Rüdiger Lainer.

Lainer says the HoHo Vienna tower shows that economic and ecological benefits are not mutually exclusive.

“The sustainability and longevity of the new wooden high rise is the result of a bundling of conceptual approaches: wood is a building material that can be used without causing major environmental damage. The flexible and user-driven arrangement of the floor plan also ensures that the high-rise gets to enjoy a long use-life.

Vienna HoHo fact-file

Owner/client: Cetus Baudevelopment – part of the Kerbler Group

Planning of support structure, building physics and building services engineering: RWT & ZT

Fire protection engineering: Kunz - die innovativen Brandschutzplaner

Gross floor area: 25,000m2

Rental space: 19,500m2

Size of property: 3,920m2

Type of building: High-rise using innovative wood construction technology

Number of floors: 24 floors

Height: 84m (276ft)

Start of construction: Autumn 2015

“Even before it was clear that we would build the HoHo Vienna, we owned four construction sites with respective land use permissions in Aspern Die Seestadt Wiens, a new multifunctional urban district in the north east of Vienna. As the new district is a part of Vienna’s smart city initiative, we also wanted to build an innovative and sustainable skyscraper there,” Palfy tells New Civil Engineer.

“Since the beginning it was clear that we wanted to build a sustainable and innovative skyscraper in line with the sustainability concept of Seestadt Aspern. Therefore we developed a new concept for the building with wood,” she adds.

A sustainable structure is only going to be sustainable if it can resist the worst case scenario – a fire. 

“Contrary to steel and concrete, CLT adds to the fire load in the building. This must be considered in the fire safety planning,” says Alexander Kunz, head of fire protection engineering for the project. “On the other hand, the stability of CLT in case of fire can be calculated very well. CLT needs no protection against fire with a special coating or insulation and has therefore an advantage over steel framed buildings. Steel structures collapse at temperatures around 600°C when they are not protected against it.”

160609 Vogelperspektive Sued West copyright RLP Ruediger Lainer   Partner

160609 Vogelperspektive Sued West copyright RLP Ruediger Lainer Partner

A bird’s eye perspective from the concept stage on the HoHo’s location within the wider development. [Copyright RLP Ruediger Lainer Partner]

“The most important part is the design of the joints between walls, beams and ceilings. The technical design has to be developed by fire safety engineers and structural engineers in close cooperation. Additionally the flammable components of the construction itself have to be evaluated in comparison to non-flammable materials and considered in the fire safety planning and the resulting concept for the building,” he adds.

While the HoHo continues to rise, the University of British Columbia, Vancouver is developing an 18-storey, 53m tall students hall of residence that uses CLT for floor plates, ceilings and walls. The building is set for completion in September 2017. Work is being undertaken by structural engineers Fast & Epp, while GHL Consultants is providing advice on building codes.

In Amsterdam, Arup is working on 73m residential tower called the Haut. The building is scheduled for completion in late 2017. 

Back in the UK, Ramboll is working on the 32m high Dalston Lane residential development in east London, which is due for completion this year. 

So if you put to one side the marketing material, and the continual egotistical competition to be the tallest in the world (if only for a moment), the pattern that emerges is that CLT is becoming a common choice for larger, taller structures.


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