Vibrations in Lightweight Buildings - Perception and Prediction

Sammanfattning: When the Swedish construction code (in 1994) allowed wooden multi-storey buildings to be built, this type of lightweight construction became popular due to its low cost and ease of construction, and also because wood is a plentiful resource in Sweden. Drawbacks in such buildings are disturbing vibrations and noise propagating in the construction, especially through junctions. In lightweight constructions using timber floors, vibrations can cause some nuisances for the inhabitants and complaints are often reported. Still, no vibration limits are given in any international standard due the complexity involved, simply certain guidelines and guide values being suggested instead. The vibrational response of wooden buildings has therefore become an issue to be tackled during their design phase. The aims of the present Licenciate dissertation can in general terms be divided into two basic categories: the development of indicators of human exposure to floor vibrations, and the development of numerical prediction tools for the verification of vibratory and acoustic performance before a building is actually put up. The appended publications Paper A and Paper B, aimed at supplementing the lack of existing studies addressing human response to floor vibrations. In order to obtain a better estimate of an acceptable level of vibrations in dwellings, measurements on real floors while people walked on the them, as well as when they sat down while another person was walking, were performed, measuring the accelerations, velocities and deflections they were exposed to. Indicators of human response to vibrations were extracted by determining relationships between people's answers to questionnaires about their perception and experience of the vibrations, and different parameters as determined by measurements. Several indicators were found to describe people's answers to questions both regarding vibration annoyance and vibration acceptability. Also, the applicability of several serviceability criteria found in the literature was checked. Ultimately, it was shown that multilevel regression, not widely used as yet in this field, can be a valuable tool for modelling repeated measures data that involves substantial inter-individual differences in rating, as the case of our study. On the other hand, there still exist no reliable methods for predicting the vibratory and acoustic performance of a lightweight building. Nowadays, product development is carried out on an empirical basis, involving both observations and the experience of engineers. Time and costs can be reduced by addressing, during the design phase, issues of vibration, for instance by using numerical methods such as finite element simulations as prediction tools. These predictions tools allow one to simulate buildings before they are built so as to examine their vibratory and acoustic performance. Development of such accurate finite element prediction tools is also dealt with in this work. In line with this, finite element models of a prefabricated timber volume element based building were created in the appended Paper C, the flanking transmission occurring being specifically analysed. Also, in the basis of conclusions drawn in that study, a method for extracting the properties of elastomers was developed in Paper D, so as to have reliable assessments of the material properties involved as input for the finite element models employed. This was done through performing analytical calculations, and carrying out finite element simulations and mechanical testing in a uni-axial testing machine. More adequate knowledge of the vibrational performance of lightweight wooden buildings such as obtained here by use of measurements and of finite element simulations is seen here as paving the way for further development in this area.