Project: House Limnologen

More about the project

General
The buildings at Limnologen have been constructed in 2007-2009 and are the oldest apartments buildings in Växjö in cross-laminated timber (CLT). The four, almost identical, buildings are timber-concrete hybrid buildings with the bottom floor in concrete and the floors 2-8 in timber. The inner and outer walls are made from CLT, including the elevator and staircase shafts. The floors are constructed in a two-level system.

The buildings were constructed in sequence, all with a weather protection by means of a tent on the upper floor where construction works were ongoing. The facades were added before the tent moved upwards and construction works on the next floor began.

Limnologen were the first buildings in the area of Välle Broar in Växjö which is dedicated to timber construction. The property developer was Midroc, now Granitor, who took on the challenge of realizing the multi-story buildings in timber, together with the Växjö-based architects from Arkitektbolaget. At the time of construction, Limnologen were the tallest multi-story residential buildings made from timber both in Sweden and the Nordics.

Early research
During the planning stages for Limnologen, discussions between the developer, the municipality as well as Linnaeus University (then Växjö University) and SP (now RI.se) led to the decision to scientifically follow the project. Collaboration was established with the Department of Building Technology, the forestry and timber engineering department and the department for mechanical engineering at Växjö University as well the TräTek division from SP.

The part on structural health monitoring resulted in two installations: in House 2, a system for monitoring settlements between floors was established; in House 3, moisture aspects were taken up and sensors installed. By this, information on, e.g., the moisture level at construction, the dry-out processes in the first years, annual variation in moisture, as well as the vertical settlements due to moisture changes and creep phenomena. The measurements spanned from 2009 to 2017 when the logging system had to be removed, the sensors were all left in place though.  

In the first years, also tests of the dynamic performance of Limnologen were performed. These included tests of floor elements alone with respect to sound and vibration, but also to check the overall, global behavior. For this, ambient vibration tests were conducted together with operational modal analysis for evaluation.

Continued SHM
As part of the establishment of the SHM-group, ideas came up to continue the measurements at Limnologen again. As all sensors were still in place and the cabling was also intact, there were good chances for a restart. A continuation of the measurements would allow to obtain information from one of the oldest CLT-buildings.

Development works are currently ongoing to be able to read the older sensors which are based on different data transfer protocols as the newer system used for more recent projects.

Dynamic performance
Also, dynamic testing was taken up again at Limnologen. Using the portable, cable-less acquisition system, such ambient vibration tests can be performed easily and with minimum disturbances to the people. The close distance to the buildings allows for quick deployment in case of favorable conditions, e.g., at higher wind rates.  

The dynamic tests aim to gain knowledge in three ways: a) obtaining the modal parameters for the actual buildings in high detail; b) comparing the four buildings with each other to see how different the performance for almost identical buildings is; and c) getting information of the modal parameters over a full year to see eventual seasonal variation,

During spring 2023, preliminary tests were performed to check the conditions ad to create a preliminary design model. Since summer 2023, tests are ongoing about once a month. In November 2024, a permanent system in one of the buildings was also installed.

Acknowledgements
We’d like to thank all partners involved in allowing us this research project. We are grateful for the support from the Södra Forskningsstiftelse for financial support as well as both Housing Cooperatives at Limnologen for the possibility to perform the tests.

The project is part of the research in the Structural Health Monitorering research group within the field of building technology and is included in the Linnaeus University Knowledge Environment: Green Sustainable Development

Project members