Good vibrations in timber construction

Thomas Hillberger has had an impressive career path – from graduating from HTL Bregenz with a degree in mechanical engineering/industrial engineering to a bachelor's degree in civil and environmental engineering from the University of Innsbruck, to two master's degrees: one in environmental engineering with a specialisation in energy-efficient construction and one in civil engineering with a specialisation in structural engineering. 

His professional career took him to the timber construction department at the University of Innsbruck as a university assistant. There he worked on a number of innovative research projects – from CFix, a novel screw connection system for timber construction, to Fold2Bend and his current project Good Vibrations, which deals with active vibration reduction in solid wood ceilings.

His research interests range from person-induced vibrations in timber construction to the use of artificial intelligence in construction, programme-supported evaluation of test results and energy-efficient construction.

Thomas Hutzinger (SIHGA GmbH):
What was the starting point for your work – the specific idea for an active vibration damper or the fundamental analysis that timber structures tend to produce undesirable vibrations in certain cases?

Thomas Hillberger (University of Innsbruck):
At the beginning, we were faced with the challenge that solid wood ceilings are often constructed with greater thicknesses than would be necessary in terms of the load-bearing capacity of the structures. In many cases, the vibration verification is the decisive factor here. We wanted to reduce this dependency explicitly, so how the problem was solved was secondary at first. However, previous studies and literature research showed the potential behind active vibration reduction. This led to the decision on how we wanted to solve this challenge.  

Thomas Hutzinger (SIHGA):
Was there a clearly defined trigger for your dissertation, or did the topic develop gradually in the course of your previous research activities?

Thomas Hillberger (University of Innsbruck):
There was no clearly defined trigger. The issue was on the table, and my previous education and work experience made it possible to consider active vibration reduction as a dissertation topic. Of course, my personal interest in this area was also very helpful. Thomas Hutzinger (SIHGA):
How did you go about selecting project partners and securing the necessary resources for Good Vibrations?

Thomas Hillberger (University of Innsbruck):
At the beginning, we asked ourselves which companies might be interested in supporting such an innovative and perhaps somewhat unusual project in timber construction. Our very positive experiences working with SIHGA on previous projects led us to bring our colleagues in Blau on board for this project. Areas such as moisture monitoring showed us that they too are thinking outside the box and also have the necessary expertise in processing measurement data. 

Thomas Hutzinger. (SIHGA GmbH):
Which aspects presented the greatest challenges at the beginning – technical development, financing or the complex material properties of wood?

Thomas Hillberger (University of Innsbruck):
As you can imagine, the biggest challenge was the active element – the hardware, so to speak, and the interaction between the measurement technology and the control of the linear motor. It must always be borne in mind that for a trained civil engineer, the implementation and development of an electromagnetic vibration damper, including the necessary control system, is a somewhat greater challenge than the mechanics and timber construction itself. Nevertheless, the dynamic behaviour of ceiling systems and person-induced excitation in the theoretical principles and in the implementation of active vibration reduction are also not easy to grasp. What I mean to say is that there were plenty of other challenges, but with sufficient motivation, they can be overcome. 

Thomas Hutzinger (SIHGA GmbH):
Were there phases in the course of the project when the achievement of the objectives seemed to be at risk, and how did you deal with this?

Thomas Hillberger (University of Innsbruck):
I think that many people who complete a dissertation or, more generally, a project lasting several years can look back on phases in which the project threatened to fail. Of course, I also experienced such low points. What helps in such situations is confidence in your own abilities, but above all personal and professional support. This makes it easier to overcome such difficult times. Another important factor is variety. Both sporting activities and additional tasks at work, such as teaching, enabled me to rearrange my thoughts and view challenges from a different perspective. 

Thomas Hutzinger (SIHGA GmbH):
Can you explain how the active vibration damper works in a way that is understandable to both experts and laypeople with an interest in technology?

Thomas Hillberger (University of Innsbruck):
The dynamic behaviour of ceilings is based on the fact that the ceiling mass is set in motion and, depending on certain geometric and dynamic parameters, the structure begins to vibrate. This force excitation can be caused, for example, by people who set the structure in vibration as a result of their movement. However, this does not involve classic sound insulation measures, but rather low-frequency vibrations in the range below 30 Hz. These can be perceived as unpleasant, especially by people on the ceiling. Experimental investigations can measure response variables such as deflection, velocity or acceleration. Measured values of vibration acceleration are also used to assess the vibration behaviour. In our project, we use the vibration acceleration measurement data to generate a dynamic force of the moving mass of the active element, which acts against the defined response variable and thus reduces the vibration acceleration in the period under consideration. The required dynamic force is generated by linear motors, which accelerate a defined mass with a specific acceleration in the corresponding direction.  

Thomas Hutzinger (SIHGA GmbH):
In which area of application do you see the first possible uses – in multi-storey timber construction or in smaller construction projects with increased requirements for user comfort?

Thomas Hillberger (University of Innsbruck):
In new construction, this will be multi-storey timber construction. Where a lot of timber is used, a lot can also be saved, and this technology may even enable the construction of an additional storey.

Thomas Hutzinger (SIHGA GmbH):
What specific benefits do you expect this to bring for timber construction – for example in terms of safety, sustainability or comfort? 

Thomas Hillberger (University of Innsbruck):
Our focus is on improving usability and thus mainly on the comfort of those people who are on the ceiling. In contrast to safety-related systems, where a failure would have serious consequences, this is less important in the present case. Nevertheless, care must be taken to ensure that the systems function properly and that there are no prolonged failures. The definition of additional limit values enables the unit itself to be protected. Sustainability also plays a role in terms of the resource-efficient use of building materials, but must be weighed against the electrical energy required.  

Thomas Hutzinger (SIHGA GmbH):
The system is currently designed for flat BSP ceilings – to what extent can it be technically transferred to wood-concrete composite ceilings, and what adjustments would be necessary for this?

Thomas Hillberger (University of Innsbruck):
It should also be possible to use this system for wood-concrete composite ceilings. Adjustments to this effect could include an increase in the dynamic force applied, although this mainly depends on the excitation and the people on the ceiling. However, further research into active vibration reduction is needed on this topic. Access for maintenance work is also essential. As with pure cross-laminated timber elements, this must be guaranteed. 

Thomas Hutzinger (SIHGA GmbH):
What possibilities do you see for adapting the system to different load situations in the future through the use of artificial intelligence?

Thomas Hillberger (University of Innsbruck):
AI offers new opportunities for problem solving in many areas of engineering. However, it is not a panacea for every area of everyday life. Nevertheless, an improvement in active unity can also be achieved here. As already mentioned, excitations could be detected and subsequently the amplification factors on which the vibration acceleration is based could be adjusted accordingly. Furthermore, it should be possible to determine the optimal timing and intensity of counteracting impulses. However, this requires further data collection. With the current prototype, such adjustments of certain parameters can be made very easily via Bluetooth.

Thomas Hutzinger (SIHGA GmbH):
To what extent could the widespread application of this technology improve the vibration characteristics of wooden buildings in the long term?

Thomas Hillberger (University of Innsbruck):
As already mentioned, the focus in new construction is on multi-storey timber construction. The savings in material can in turn lead to an increase in competitiveness compared to other materials such as reinforced concrete. In addition, however, I also see great potential in the renovation of existing properties or when serviceability limits cannot be met in terms of vibration behaviour. This can also be the case if the use of the property changes and, for example, an attic is to be converted into a separate residential unit. Another example is when the comfort of a flat is compromised due to external disturbances, such as a tram.