Sustainable Lightweight
Flagship project for hybrid timber construction: Grand Central, Vienna
Wojciech Tomczak
Sustainable, light, and flexible to use: Wood offers many advantages as a building material. And at the “Grand Central” office complex, the hybrid timber construction method is also the key to meeting the challenges facing the loadbearing structure.
“Grand Central” is a particularly sustainable and flexible building complex that enjoys optimal transport connections due to its location right next to the Vienna Floridsdorf transport hub. With two building elements and a total area of 12,000 m2, the complex provides Vienna’s 21st District with urgently needed rental office space.
The 175-meter-long and 20-meter-wide, six-story new building perfectly exemplifies the advantages of hybrid timber building. As it was built directly above the turnaround area of the metro, as a result of which it has to be supported by the existing underground tunnel, its weight had to be reduced – and this was made possible by the combination of the composite building method and lightweight elements. This hybrid timber construction on the basis of prefabricated modules also permits a high level of flexibility in the design of the interiors – which was one of the client’s central requirements.
Maximum flexibility
Thanks to the use of a frame structure with composite timber slabs, reinforced concrete columns, and a plastered cross-laminated timber facade, the spaces can be flexibly divided and easily adapted to meet different user needs: From open plan to individual offices, everything is possible.
The hybrid timber construction method also facilitated a highly-flexible building process. The use of timber as an invisible building material enabled us to work more efficiently and reduce costs. As there was no specific focus on the visible aspect of timber, we were able to handle it more flexibly, which is a huge advantage when working with particularly complex elements, such as composite timber slabs in combination with in-situ concrete. A further advantage is that timber permits errors. This meant that the few incorrectly dimensioned elements that were delivered could be adapted without problems on site.
The most important argument for timber was its low weight and the second was speed. Thanks to the high level of prefabrication of the elements, we were able to build considerably more rapidly.
Siniša Macedonić
Architect, Lead Project Manager in Vienna
A “balancing act” on the underground tunnel
As Grand Central is located right next to a busy transport hub, our design paid particular attention to noise protection and the electrostatic separation of the building – which permitted an optimal level of comfort in the interiors.
The grounding of the building on the metro turnaround area was a particular challenge for the loadbearing structure, as the roof of the tunnel had to be decoupled from the building and all the weight diverted to its loadbearing structure. Alongside the necessary vibration protection, it also has to react to the impact of the wind, tilting, and earthquakes.
We met the load transfer target by building a 15-meter-long pile grid that absorbs the loads and transfers these to the corresponding points on the columns and the side walls. The columns stand on this grid. The exact locations of this load transfer were calculated in advance with the help of the digital measurement of the underground tunnel.
As the metro is powered by a direct current and the building by an alternating current, these were separated electrically by a film inserted between the pile grid and the roof of the tunnel. This ensured that steel elements such as reinforcing bars do not corrode due to the leakage currents that can arise when different forms of electric current come together
In order to optimize vibration protection we took a range of measurements of the shell of the tunnel roof in advance, as a means of evaluating the vibration and secondary sound immissions and defining target levels of protection.
Wojciech Tomczak
Engineer, Group Leader, Structural Engineering in Vienna
Composite timber-concrete slabs
A composite timber-concrete slab with PFEIFER Hybridbeam® beams proved to be the ideal solution for the slab above the standard floors. The building is braced by the two reinforced concrete cores in each element. These composite timber slabs form a rigid horizontal element and transfer the effects of wind, tilting, and earthquakes to the vertical walls. The columns and beams are formed as frames and contribute to the horizontal stiffening.
The composite timber slabs also reduce the overall thickness of the loadbearing slab construction. The composite steel beams are integrated into the slab, permitting smooth ceilings and higher spaces, and simplifying the installation of the building services. A further, major advantage of composite timber slabs is their excellent levels of noise and vibration protection.
