During the last years the interest in multi-storey timber buildings has increased and several medium-to-high-rise buildings with light-weight timber structures have been designed and built. Examples of such are the 8-storey building “Limnologen” in Växjö, Sweden, the 9-storey “Stadthouse” in London, UK and the 14-storey building “Treet” in Bergen, Norway. The structures are all light-weight and flexible timber structures which raise questions regarding wind induced vibrations. This paper will present a finite element-model of a 22 storey building with a glulam-CLT structure. The model will be used to study the effect of different structural properties such as damping, mass and stiffness on the peak acceleration and will be compared to the ISO 10137 vibration criteria for human comfort. The results show that it is crucial to take wind-induced vibrations into account in the design of tall timber buildings.

The impact ball has shown to give excitations in close resemblance with the excitation from a human step. However due to practice and practical measurement reasons, it is interesting to use the tapping machine in low-frequency measurements. Here, the two excitation techniques; the tapping machine and the impact ball, are compared in terms of statistical dispersion. In the AkuLite project light weight apartment buildings were measured using a tapping machine and a (Japanese) impact ball in the low frequency range down to 20 Hz. The results showed that the tapping machine gives more narrow/better confidence interval in the test compared to the test using one excitation point together with the impact ball. The t-test of the consistency of the difference between the impact ball and tapping machine for the same measurement objects shows weak correlation, which implies that the results from the tapping machine are not normally possible to be interchanged with impact ball results and vice versa, without using a correction factor.

Using wood as the main construction material is a potential solution to achieve sustainable buildings. Previous research has shown that frequencies below 50 Hz are of significant importance for the perception of impact sound by residents living in multi-story buildings having light weight wooden frameworks. The standards used for impact sound measurements today are developed for diffuse fields above 50 Hz. For instance due to requirements concerning wall reflections, these methods are not applicable for low frequencies within small rooms. To improve measurement methods, it is important to know the nature of the full sound distribution in small rooms having wooden joist floors. Here, impact sound measurements with microphone arrays are made in two small office rooms having the same dimensions. The rooms represent two extremes in design of joist floors; one with closely spaced wood joists and the other with widely spaced joists. An impact ball is used for excitation the room being measured from the room above. The results show that there are significant variations in the sound pressure, especially in the vertical direction. Here, measurement techniques of impact sound in the low frequency range in small rooms in wooden buildings are evaluated and potential improvements are proposed.

In timber housing constructions, vibrations can be a nuisance for inhabitants. Notably, the vibrational response of wooden floor systems is an issue in need of being dealt with more adequately in the designing of such buildings. Studies addressing human response to vibrations are needed in order to be able to better estimate what level of vibrations in dwellings can be seen as acceptable. In the present study, measurements on five different wooden floors were performed in a laboratory environment at two locations in Sweden (SP in Växjö and LU in Lund). Acceleration measurements were carried out while a person either was walking on a particular floor or was seated in a chair placed there as the test leader was walking on the floor. These participants filled out a questionnaire regarding their perception and experiencing of the vibrations in question. Independently of the subjective tests, several static and dynamic characteristics of the floors were determined through measurements. The ultimate aim was to develop indicators of human response to floor vibrations, specifically those regarding vibration acceptability and vibration annoyance, their being drawn based on relationships between the questionnaire responses obtained and the parameter values determined on the basis of the measurements carried out. To that end, use was made of multilevel regression. Although the sample of floors tested was small, certain clear trends could be noted. The first eigenfrequency (calculated in accordance with Eurocode 5) and Hu and Chui׳s criterion (calculated from measured quantities) proved to be the best indicators of vibration annoyance, and the Maximum Transient Vibration Value (computed on the basis of the accelerations experienced by the test subjects) to be the best indicator of vibration acceptability.

Natural frequencies, damping ratios and mode shapes of a prefabricated timber floor element have been assessed experimentally in laboratory with different boundary conditions and in situ (in field) at different stages of construction. In laboratory the change in modal parameters was studied with free-free boundary conditions and simply supported on two sides. Three different simply supported tests with changes in boundary conditions were carried out; the floor placed on the support without any fastening or interlayer between support and floor, the floor screwed to the supports and the floor placed on an elastic interlayer between support and floor. The in situ tests were carried out first on the single floor element and then on the entire floor of the room into which the floor element was built in. The damping ratio of the floor increased from 1% to 3% when simply supported in laboratory to approximately 5% when placed upon a polyurethane interlayer (Sylodyn) in situ, and to approximately 6% when fully integrated in the building. Thus the in situ conditions have considerable influence on the damping and the values assessed are very high in comparison with damping values suggested in design codes. Regarding natural frequencies it was concluded that the major change in these occur as the floor element is coupled to the adjacent elements and when partitions are built in the studied room, the largest effect is on those modes of vibration that are largely constrained in their movement.

Springiness and vibrations of timber floors are familiar to many as a ‘live’ feelwhen walking on them, especially if living in single family housing with timberframework. Since the building regulations in Sweden changed to performancedependentrequirements in 1994 the use of timber in multifamily housing hasincreased. New timber building systems have been developed and increasedbearing capacity of floors has made it possible to build with longer spans. Thelow mass of timber floors makes them more sensitive to dynamic loading byhuman activities, such as walking, running and jumping, compared to heavyfloors e.g. concrete floors. To improve vibration performance it is possible tochange the structural properties of the floors by increasing mass, stiffness ordamping properties. The most practicable solution is to increase the stiffness.Improved damping is also highly effective, but is difficult estimate and designaccurately since it originates from many sources in the finished building. In thepresent thesis the effects on dynamic properties from increased stiffnesstransverse to the load bearing direction of a floor have been assessed from testsin laboratory. The effect on dynamic performance of a timber floor fromelastic/damping interlayers (polyurethane elastomers) installed in the junctionsbetween walls and floors have been assessed in laboratory and in situ. Also thechange in dynamic properties of an in situ floor has been investigated atdifferent stages of construction and compared with results from laboratory tests.The present criteria for design of timber floors with respect to vibrationperformance were developed at a time when timber floors were mainly used insingle-family housing. The traditional timber joist floors differ in structuralbehaviour from the new types of floors developed recently. The experiencedvibration annoyance by residents in single- and multifamily housing differs asthe source of vibration disturbance and those who become disturbed aredifferent. The changed conditions give cause for a review of present designcriteria. A laboratory and field study on vibration performance was conductedwith questionnaires and dynamic performance measurements. The subjectiveand objective results were correlated and indicators for vibration acceptabilityand annoyance were assessed and new vibration performance criteria andvibration performance classes were suggested.

In residential multi-storey buildings of timber it is of great impor-tance to reduce the flanking transmission of noise. Some buildingsystemsdothisbyinstallingavibration-dampingelasticinterlayer,Sylomerror Sylodynr, in the junction between the support andthefloorstructure.Thisinterlayeralsoimprovesthefloorvibrationperformance by adding damping to the structure. In the presentwork the vibration performance of a floor with such interlayershas been investigated both in laboratory and field tests. A pre-fabricated timber floor element was tested in laboratory on rigidsupports and on supports with four different types of interlayers.Theresultsarecomparedwithin situtests on a copy of the samefloorelement.Theeffectonvibrationperformancei.e.frequencies,damping ratio and mode shapes is studied. A comparison of theinsitutestandthetestwithelasticinterlayerinlaboratoryshowsthatthe dampingin situis approximately three times higher than on asingle floor element in the lab. This indicates that the dampinginsituisaffectedbethesurroundingbuildingstructure.Theachieveddamping ratio ishighly dependent onthe mode shapes. Mode sha-pes that have high mode shape coefficients along the edges wherethe interlayer material is located, result in higher modal dampingratios. The impulse velocity response, that is used to evaluatethe vibration performance and rate experienced annoyance in thedesign of wooden joist floors, seems to be reduced when adding elastic layers at the supports.

In lightweight structures it is common to use damping material in junctions to decrease sound transmission. In field measurements, the damping properties of the structure are easily overestimated due to the omnipresent energy losses to the surroundings. Thus, reliable estimates of structural properties cannot be guaranteed.

Vibrational tests were done on a full scale wooden construction, consisting of a floor and supporting beams, representing walls, to investigate the effect of different junctions. Totally seven different setups were made using the same building components. In one setup the floor and the walls were screwed together, in five setups different elastomers was positioned between the floor and the walls and in the last setup the floor was resting free on top of the walls. A shaker, with pseudorandom excitation, was used for the excitation of the structure and accelerometers were used for response measurements. The effect of the junction was investigated by studying the acceleration levels in the edge part of the floor-wall junction in different directions.

Modal data, extracted from test data using experimental modal analysis, form input and validation data for the following finite element (FE) analysis. Two FE models; modeling one elastomer and the screwed setup, are used for the studies.

The aim was to study if the eigenmodes rendering the acceleration levels are similar in test and in analysis, using common material properties.

The results from correlation between test and analytical results show that the material properties of the wood need to be known better; more sophisticated models are needed to fully simulate the dynamic behavior of the structure. Anyhow, with the used properties the mode shapes are captured fairly well in the lower frequencies. Furthermore, the experiment shows that the damping properties of the junction material have a major influence on the behavior of the structure.