Vertical village with alleyways and plazas
With its diameter of 137 m and its height of 28 m Vortex student housing seems almost monolithic. Jean-Pierre Dürig derived the circular floor plan from the Olympic rings. A close-up view reveals that the building appears surprisingly dynamic, resembling an athlete whirling in the air. The 916 rooms aren’t simply stacked on horizontal platforms along eight storeys. Instead, they spiral upwards continuously, all the way from the green interior courtyard to the roof terrace with its view of Lake Geneva.
After its initial use, the spatial concept continues to be a success. Currently, the building serves as housing for 1100 students and guests of the University of Lausanne and constitutes a place of identification amongst scattered campus buildings. The architect named his design Vortex, a whirlwind. Considering the moderate 1 % degree of inclination of the access balconies, that seems slightly hyperbolic. It takes 25 minutes to walk along the 2.8 km long ramp from the ground floor all the way up to the rooftop café. The green interior courtyard serves as a park, an event area and a village square all at once. In the north the level lawn ascends by 1.70 m in five terraced steps before it connects to a two-storey event space. Fountains and benches invite visitors to stay and relax. The up to 2.30 m wide ramps that encircle the courtyard are reminiscent of the galleries of a baroque theatre hall. Twice per storey they are connected by passages to the 1.60 m wide access balconies along the outside perimeter. Each storey features shared kitchens and laundry rooms. The ground floor is enlivened by a restaurant, a café, a nursery, shops and services facilities. Passages on three sides turn the ring-shaped building into a permeable structure and mesh it with the surrounding natural environment.
Concept and realisation
The ring-shaped floor plan comprises rooms organised within an orthogonal system in the form of modules. Due to the uniform grid width of 3.21 m one might expect a high degree of repetition and economically efficient realisation. On a detail level, the geometry actually wasn’t that simple as the clear concept might suggest: The modular structure needed to be flexible enough in order to accommodate the different apartment configurations, ranging from single room with shared kitchen along the corridor to shared apartments and guest apartments with up to four rooms. The cantilevering, circular ramps had to be mastered in terms of structural engineering. Fireproofing required altogether six staircases next to the elevator shafts in order to minimise emergency exit distances. Housing units weren’t realised in the form of inset, prefabricated timber boxes but instead, as a sequence of reinforced concrete walls. The interval between walls measures 6.42 m and equals two modules. All other partition walls are comprised of gypsum board drywall construction. Only the sanitary pods were created as prefabricated modules. The concrete boxes were delivered to the construction site complete with tiled surfaces, shower bathtub and all bathroom fittings ready for connection. The facades are clad in spruce siding and provide the reinforced concrete building with a tangible and warm expression. Elements were prefabricated individually for every apartment type and feature ceiling height glazing with sun protection roller blinds, an openable ventilation flap, an air intake for single flow controlled mechanical ventilation as well as a spruce door leaf.
A spiral model: limits of practicability
In 2015 Jean-Pierre Dürig won the architectural design competition and two years later the client launched a realisation competition, which the architects of IttenBrechbühl won, in cooperation with the general contractor, Losinger Marazzi. Neither did the client at any time determine that the BIM method should be used, nor that the planning data should serve purposes of facility management. In the tendering process the combined application as ICE-team (BIM integration in higher and continuing education) convinced the client, not only due to the proposed technical solution, but also because the partners proposed a demonstrable and clearly structured planning and construction process. In previous projects, such as the IOC headquarters in Lausanne, IttenBrechbühl already experienced the advantages of the BIM method. For the seasoned project manager Guillaume Schobinger, it was the first project with BIM: “The great advantage for us was that we could show the client that we were in command of the building geometry very clearly and at any given time.” For the general contractor, Losinger Marazzi, BIM is common practice for large-scale projects. The tight schedule, cost certainty and managing thousands of different construction components were criteria that motivated them to use BIM for planning. “Our client told us to maintain the image and quality of Jean-Pierre Dürig’s design and at the same time save time and costs”, Miguel Bermudez recalls, BIM manager at Losinger Marazzi. However, the responsible planners were less determined to optimise the design concept, but rather, the construction methods and planning processes. The aim was to build the spiral and the orthogonal apartment grid by requiring as few changes as possible.
Master and partial models
The basic questions on how to efficiently create the 3D model were addressed by Schobinger and Bermudez within in-depth preliminary talks. The decisive challenge was to reduce data size. The planners soon reached the limits of the BIM software. It generally allows separating floors stacked on top of each other into partial models. However, in the case of the continuous spiral of Vortex, this was not possible. The architect and the general planner decided where to create sensible partitions. The six staircase cores were selected as anchors to subdivide the ring-shaped plan into six segments. Except for electrical wiring for lighting, no horizontal installations or service lines crossed over from one segment into the next. This permitted separating the segments from each other, similar to six individual buildings.
Individual 3D models were created for the reinforced concrete structure, calculation of building cubage, layout of service lines, prefabricated sanitary pods and the facade. “Altogether we had to work on more than 50 partial models”, Bermudez adds. By far not all construction components were actually modelled in 3D. “Construction details from the individual contractors weren’t relevant to the master model. They would have only increased data size. In order to identify absolute dimensions of fixed glazing, ventilation openings and entrance doors within the timber facades, we merely gave the contractor the parameters and interdependencies. For the 22 different types of completely pre-installed concrete bathroom pods, neither the tile layout nor the type of bathroom fixtures were important for the master model, but rather, the exterior dimensions and connections to our service line network.”
Data exchange with openBIM
The Open-BIM principle permitted using different BIM software solutions tailored to specific disciplines. In order to import partial models without any interface problems, they were converted into the IFC format. “2D horizontal sections weren’t actually required within the 3D planning process”, Schobinger explains.
The interdependencies in the vertical dimension are highly complex. Typical, successive floors were identical in plan. Yet, the transitions from the basement level to the partially double height ground floor and from the ceiling between the ground floor to the apartments above were highly complex, due to the high amount of ventilation technology installed in the shared spaces. The solar unit on the roof also exceeds the typical degree of complexity of student housing: The mono-crystalline glass foil modules are oriented along an east-west axis in order to optimize energy gains and produce 328 kWp of power and 360 MWh/a yield along 2000 m².
Collisions between either electrical and ventilation ducts or the shell construction were automatically indicated by use of specific software. The BIM collaboration format BCF guaranteed that spatial overlaps were identified and displayed. Annotations can be added in the 3D model with a freehand tool.
During the planning process, changes occurred repeatedly. The BIM method, however, required additional discipline. “When using BIM with a very tight schedule, mistakes can no longer be corrected. The advantage is that decisions made can no longer be questioned, either”, Schobinger explains. “In order to make sure that the building volume was maintained precisely despite any and all changes, we defined the building edges along the circumferential ramps as unchangeable borderlines. From start to finish, nobody could change them.”
Using BIM transforms the staff structure of construction firms. At Losinger Marazzi, 20 engineers worked on Vortex in planning and execution. The general contractor had 60 workers on the construction site. Including the other trades, up to 100 construction workers were on site simultaneously. Intelligent construction site logistics and the industrialisation of traditional craftsmanship-oriented trades contributed to the success of the project: First, the concrete slabs were poured, floor by floor, including the two circumferential ramps and their pre-assembled steel railing. As a result, no scaffolding was required. 60 concreting sections along the ramp comprise a complete circle. These column-free access balconies are supported by cantilevering steel beams following the concrete partition centre lines. Within only 12 days the concrete ceiling, the in-situ concrete partitions and the bathroom pods of one storey were completed. For reasons of fire protection the sanitary pods consist of thin concrete walls, floors, and ceilings. Altogether 916 of them were required, according to 22 different types, in order to realise the diverse set of floor plans. Planning them was a separate BIM project within the project.
In order to translate the data of the digital twin onto the construction site in a precise manner, Miguel Bermudez used BIM 2 Field. It allowed merging the 3D data points of the model with the workflow of the land surveyors and let them stake out the site accordingly.
