Complex installations, logistics and tricky loads were challenging in the Aquila prefab project in Uppsala. In addition, the conditions for the assembly order of the frame and facade changed in the middle of the project, which meant special solutions on already delivered and cast elements.
- The project required close and advanced collaboration with a large number of stakeholders. We would never have been able to solve this in any other way than working with the buildable model in Tekla Structures in combination with Trimble Connect and Impact," says Erik Åkerman, structural engineer at Looström, and project manager for the construction of the concrete frame.
The Aquila project comprises 170 new student and researcher residences totaling 13,000 square meters in the Rosendal district on the outskirts of central Uppsala. The building is both scenic and directly adjacent to a university campus and is scheduled for completion in 2025.
- Aquila has a U-shape with one high part with 12 floors and two parts with six floors. The size and design of the apartments will suit everything from single occupants to families, and therefore the building will be unusually varied for a prefabricated project," says Erik Åkerman, structural engineer at Looström, who was responsible for the concrete frame.
Varierande laster
The variations in the surfaces mean that there are no straight lines of windows, creating complex loads throughout the building. The ground floor has large windows, so special solutions were required for the frame to handle the loads from above.
Erik explains that the client Akademiska Hus wanted an RD slab, i.e. a solid concrete floor slab, which is quite unusual and particularly challenging due to its length.
- We solved this by working with prestressed D-plates and prestressed RD-plates that are over ten meters long to speed up the assembly process. Spans and castings were crucial to this choice," explains Erik.
The sewage system for the toilet and kitchen was to be cast into the slabs in the factory, which made it imperative that the slabs were fitted precisely as the tolerances were tight, as were the embedded drains and electrical installations. This was solved by working closely on the buildable Tekla model with prefabrication supplier K-prefab.
Concrete clad with wood
Uppsala municipality required that the new buildings in the area, which is also the southern entrance to the city center, should be characterized by wood.
- We helped the client develop a hybrid solution, combining concrete columns with cast boards to give a wood-like effect, and glulam beams.
The solution was to change the entire floor system to a column-beam system instead and hide it so that it looks like external walls. Some walls also needed extra analysis and reinforcement to cope with the load when the loads abruptly hit a door or window. The large window sections would otherwise take up all the concrete, leaving nothing to build on and thus unable to carry the loads needed.
- To achieve the wood-like façade, half-sandwich walls with factory insulation are used. Special sleeves are cast into these walls, and then the wooden cassettes are fitted in place to create the wooden look of the whole facade. In this case, it was special that the wooden cassettes should look natural, so we had to draw up a matrix for the whole facade to make sure everything would look correct and also take tolerances into account. We needed to think about what would happen if the wall was installed a few centimeters wrong, and how it would affect the wooden cassettes. Therefore, everything was designed and planned with a certain tolerance in the façade to allow for adjustments," explains Erik.
Better collaboration and economy with Tekla Structures
Overall, the project has been much more complex than it seemed, but it has been solved thanks to close collaboration between the actors around the model. Erik Åkerman and his team are experienced Tekla users and see this as a prerequisite for completing this complex assignment on time and at the right cost.
- We simply could not have solved this in any other program. The biggest benefit of working in Tekla Structures in Aquila has been the ability to bounce ideas and solve different challenges, especially when it comes to the façade fixings and tolerances.
Another major benefit of Tekla Structures was the ability to check the assembly of the wood cladding and ensure that there were no collisions or problems with tolerances. It was also important to ensure that the plumbing and electrical installations worked correctly in the complex house.
- Tekla improved the financial calculation, as the project was carried out at a fixed price and we could utilize the repeatability throughout the building. By using Tekla, we could ensure repetition and similar details on several floors," says Erik.
Communication between the project manager and our client, as well as the exchange of IFC models, has been continuous throughout the project using Trimble Connect.
- "We have used Trimble Connect a lot, including in joint review meetings, with crash analyses. There has also been an extensive review of documents by electrical and plumbing consultants throughout the project," says Erik.
Impact for industrial manufacturing
The Aquila project uses Impact software, which specializes in the planning and control of production processes in the manufacturing industry. It is used to make the model available to K-prefab. Through the "Export to Impact" function in Tekla Base Tool, the Tekla Structures model is exported to Impact and manufacturing can be planned in both production and assembly in the same model.
The Tekla models, together with the associated 2D drawings, are used to support the planning, preparation, fabrication, finishing and erection of the precast elements. They also use PXML files from Tekla Structures for cutting and bending reinforcement on their sites.
Facilitated logistics
Logistics have been a major challenge, partly due to changing conditions that meant the stability of already manufactured elements had to be recalculated.
Tekla Structures models are also used for material delivery planning, where they serve as master data for generating material order lists and reports.
- But because we can deliver things from our model via Impact, production was able to do its planning anyway. It turned out to be absolutely invaluable that we were able to see what stage each individual element is in, and that they could see where we are in our production. So the combination of a buildable model and production has been very good in this case," concludes Erik Åkerman.
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