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Structural-acoustic vibrations in wooden assemblies:: Experimental modal analysis and finite element modelling
Linnaeus University, Faculty of Engineering and Technology, Department of Building and Energy Technology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
VIBRATIONER OCH STOMBURET LJUD I TRÄKONSTRUKTIONER : Experimentell modalanalys och finit elementmodellering (Swedish)
Abstract [en]

This doctoral thesis concerns flanking transmission in light weight, wooden multi-storey buildings within the low frequency, primarily 20-120 Hz. The overall aim is to investigate how the finite element method can contribute in the design phase to evaluate different junctions regarding flanking transmission.

Two field measurements of accelerations in light weight wooden buildings have been evaluated. In these, two sources; a stepping machine, and an electrodynamic shaker, were used. The shaker was shown to give more detailed information. However, since a light weight structure in field exhibit energy losses to surrounding building parts, reliable damping estimates were difficult to obtain.

In addition, two laboratory measurements were made. These were evaluated using experimental modal analysis, giving the eigenmodes and the damping of the structures. The damping for these particular structures varies significantly with frequency, especially when an elastomer is used in the floor-wall junction. The overall damping is also higher when elastomers are used in the floor-wall junction in comparison to a screwed junction. By analysing the eigenmodes, using the modal assurance criterion, of the same structure with two types of junctions it was concluded that the modes become significantly different. Thereby the overall behavior differs.

Several finite element models representing both the field and laboratory test setups have been made. The junctions between the building blocks in the models have been modeled using tie or springs and dashpots. Visual observation and the modal assurance criterion show that there is more rotational stiffness in the test structures than in the models.

The findings in this doctoral thesis add understanding to how modern joints in wooden constructions can be represented by FE modelling. They will contribute in developing FE models that can be used to see the acoustic effects prior to building an entire house. However, further research is still needed.

Abstract [sv]

Denna doktorsavhandling behandlar flanktransmission i flervåningshus med trästomme, inom det lågfrekventa området, främst 20-120 Hz. Det övergripande målet är att undersöka hur finita elementmetoden kan bidra i konstruktionsfasen för att utvärdera olika knutpunkters inverkan på flanktransmissionen.

Två fältmätningar av accelerationer i trähus har utvärderats. I dessa har två olika lastkällor använts, i den första en stegljudsapparat och i den andra en elektrodynamisk vibrator (shaker). Det visades att shakern kan ge mer detaljerad information, men eftersom vibrationerna även sprider sig till omgivande byggnadsdelar vid fältmätningarna var det svårt att estimera tillförlitliga dämpningsdata även då shaker användes.

Fältmätningarna följdes av två mätningar i laborationsmiljö. Dessa två experiment utvärderades med experimentell modalanalys, vilket ger egenmoder och dämpning hos strukturerna. Dämpningen för dessa trähuskonstruktioner varierar kraftigt med frekvens. Extra stora variationer registreras då en elastomer användes i knutpunkten mellan golv och vägg. Den totala dämpningen är generellt högre när elastomerer används i knutpunkten mellan golv och vägg i jämförelse med då knutpunkten är skruvad. Genom att analysera egenmoder och deras korrelationer (MAC), för samma trästruktur men med olika typer av knutpunkter, drogs slutsatsen att knutpunkten drastiskt förändrar strukturens dynamiska beteende.

Flera finita elementmodeller av både fält- och laboratorieuppställningar har gjorts. I dessa har knutpunkterna mellan byggnadsdelar modellerats helt styvt eller med hjälp av fjädrar och dämpare. Visuella observationer av egenmoder och korrelationen dem emellan visar att det finns mer rotationsstyvhet i försöken än i finita elementmodellerna.

Resultaten i denna doktorsavhandling har gett förståelse för hur knutpunkter i träkonstruktioner beter sig och kan simuleras med finit elementmodellering. Vidare kan resultaten bidra till utvecklingen av FE-modeller som kan användas för att kunna se de akustiska effekterna redan under konstruktionsstadiet. Dock behövs ytterligare forskning inom området.

Place, publisher, year, edition, pages
Växjö, Sweden: Linnaeus University Press, 2013. , p. 100
Series
Linnaeus University Dissertations ; 115/2013
Keywords [en]
wooden framed structure, light weight buildings, multi-storey, flanking transmission, junction, vibration distribution, impact noise, damping, elastomers, finite element analysis, experimental modal analysis, FRF
Keywords [sv]
trästomme, träkonstruktion, träbyggnad, flervåningshus, EMA, FEM, flanktransmission, koppling, knutpunkt, vibrationsspridning, stomljud, stegljud, dämpning, elastomerer, finit elementmetod, experimentell modalanalys, accelerationsmätning, frekvensresponsfunktion, modalanalys
National Category
Building Technologies Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:lnu:diva-24562ISBN: 978-91-87427-04-6 (print)OAI: oai:DiVA.org:lnu-24562DiVA, id: diva2:607732
Public defence
2013-03-15, Södrasalen, Hus M, Lückligs Plats 1, VÄXJÖ, Sweden, 14:24 (Swedish)
Opponent
Supervisors
Available from: 2013-02-28 Created: 2013-02-25 Last updated: 2013-02-28Bibliographically approved
List of papers
1. Structural Vibrations of Wooden House Walls
Open this publication in new window or tab >>Structural Vibrations of Wooden House Walls
2006 (English)In: Journal of BUILDING ACOUSTICS, Vol. 13, no 4, p. 285-293Article in journal (Refereed) Published
Abstract [en]

The flanking transmission between apartments due to a structure borne source is studied. The apartments studied were two-storey houses with a wooden framework. Acoustic measurements are often made in new built apartments to make sure that they fulfil the building regulations. Traditional measurements give no information about the contribution of the surrounding walls to the sound transmission.

This paper describes a method of measuring flanking transmission. The acceleration levels on the receiving parts in the apartment below the source are studied. Thereby the contribution to the sound pressure in the room from each flanking part can be distinguished.

Place, publisher, year, edition, pages
MULTI-SCIENCE PUBLISHING CO. LTD., 2006. p. 285-293
Keywords
Wooden framework, Impact noise, Vibration, Accelometer measurement
National Category
Fluid Mechanics and Acoustics
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:vxu:diva-1278 (URN)
Available from: 2007-05-15 Created: 2007-05-15 Last updated: 2013-02-28Bibliographically approved
2. Evaluation of vibration distribution from a full scale measurement in an eight storey wooden house
Open this publication in new window or tab >>Evaluation of vibration distribution from a full scale measurement in an eight storey wooden house
2008 (English)In: Proceedings of ISMA2008: International Conference on Noise and Vibration Engineering / [ed] Sas, P. & Bergen, B., Katholieke Universiteit Leuven, Department of Mechanical Engineering , 2008, p. 593-607Conference paper, Published paper (Refereed)
Abstract [en]

Flanking transmission measurements has been done in an eight storey wooden building in Växjö, Sweden. The flanking transmission is evaluated by studying the vibration distribution from a well defined source to the flanking surfaces in the room one floor below. Besides the vibration distribution measurements the sound pressure in the room were measured. The measuring campaign shows that the used technique can be carried out to capture the flanking transmission in a direct and trustful way. The technique shows that peaks in the sound pressure can also be related to peaks in different surfaces frequency response functions. By calculating the energy distribution between surface elements it was shown that the roof in the examined room was the part that absorbed the most of the added energy from the source. Thereby it was regarded as the flanking part that needed an improved design most.

Place, publisher, year, edition, pages
Katholieke Universiteit Leuven, Department of Mechanical Engineering, 2008
Keywords
Wood framed structure, Vibration distribution, Flanking transmission, FRF, Modal analysis, Acceleration modes
National Category
Fluid Mechanics and Acoustics Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:vxu:diva-3560 (URN)000263409900043 ()9789073802865 (ISBN)
Conference
International Conference on Noise and Vibration Engineering (ISMA 2008), Leuven, Belgium, September 15-17, 2008
Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2015-09-17Bibliographically approved
3. FE modeling of wooden building assemblies
Open this publication in new window or tab >>FE modeling of wooden building assemblies
2010 (English)In: InterNoise 2010-Lisbon Portugal 13-16 June, 2010, p. 1-10Conference paper, Oral presentation only (Refereed)
Abstract [en]

Residential timber framed buildings have in some cases received complaints from inhabitants due to structure-borne sound at low frequencies, even if the building meets the regulations with respect to impact sound quality. This paper describes FE-analyses to evaluate the test setups of a building assembly and to prepare for the full-scale experimental modal analysis planned. By modal analysis, the dynamic properties of a structure, such as eigen modes and damping characteristics, can be extracted.

 

The test assembly consists of prefabricated wall and floor/roof timber elements. Different assembly and joining methods as well as building element are used. The eigen modes and damping differs between the assemblies investigated which influence the dynamic response in the lower frequencies. The results are carefully evaluated and planned measurements are discussed.

Keywords
Structure-borne sound, modal analysis, dynamic response, FE analysis
National Category
Fluid Mechanics and Acoustics Building Technologies
Identifiers
urn:nbn:se:lnu:diva-24561 (URN)
Conference
Inter.Noise 2010, 13-16 June, Lisbon
Available from: 2013-03-04 Created: 2013-02-25 Last updated: 2015-09-17Bibliographically approved
4. FE modeling of a lightweight structure with different junctions
Open this publication in new window or tab >>FE modeling of a lightweight structure with different junctions
2012 (English)In: Euronoise 2012-proceedings / [ed] Czech Acoustical Society, European Acoustics Association (EAA), 2012, p. 162-167Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
European Acoustics Association (EAA), 2012
Series
Euronoise proceedings, ISSN 2226-5147
Keywords
Lightweight structure finite element dynamic
National Category
Civil Engineering
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-21194 (URN)978-80-01-05013-2 (ISBN)
Conference
Ninth European Conference on Noise Control (Euronoise), Prague, 10-13 June, 2012
Available from: 2012-08-14 Created: 2012-08-14 Last updated: 2015-09-17Bibliographically approved
5. Damping Assessment of Light Wooden Assembly With and Without Damping Material
Open this publication in new window or tab >>Damping Assessment of Light Wooden Assembly With and Without Damping Material
2013 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 49, p. 434-447Article in journal (Refereed) Published
Abstract [en]

Damping elastomers are often used in lightweight wooden constructions and are believed to have good sound insulating effects. In the present study the influence on the structural behaviour by using elastomer damping material (Sylomer®) in the joints, with particular respect to footsteps and floor vibrations, has been investigated. A full scale wooden mock-up was assembled with two different joint configurations and studied under free-free boundary conditions. In the first configuration, the joints between the floor and underlying walls were screwed together. In the second configuration the floor was resting free on top of ribs of elastomer damping material, equivalent to normal building practice when this material is used. Both configurations were analysed and evaluated using experimental modal analysis, in the frequency interval 10-115 Hz.

 

The relative (viscous) damping ratios of the modes were found to be on average 1.2% for the screwed configuration and 2.1% for the configuration with elastomer damping material in the joints. The damping was found to vary significantly between modes in the elastomer case. It was found that at low frequencies damping was high for modes with large motion on the edge where the elastomer material was. At higher frequencies (above approx. 40 Hz), however, the damping for this configuration decreased. This is believed to be caused by a vibration isolation effect of the elastomer, decoupling the floor from the walls at higher frequencies.

 

To assess the differences in vibration levels between the two configurations, mean acceleration levels of well spread points on the different building parts where computed and evaluated. It was found that above approximately 70 Hz, the mean vibration level in the elastomer configuration was significantly lower than for the screwed configuration. Below 70 Hz, however, for many frequencies the mean vibration level for the elastomer configuration was significantly higher than for the screwed configuration (as should be expected in vibration isolation). Problems with springiness and footsteps are due to loads in the frequency range of 10 to 50 Hz, this could indicate that elastomers, used as in the present study, could worsen these types of problems, although improving higher frequency acoustic performance.

Keywords
Elastomer, Sylomer®, Joint, Wooden construction, Damping, Experimental modal analysis, EMA, Footstep, Floor vibration, Springiness
National Category
Building Technologies Fluid Mechanics and Acoustics
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-24554 (URN)10.1016/j.engstruct.2012.11.026 (DOI)000317528800035 ()2-s2.0-84871772540 (Scopus ID)
Available from: 2013-02-25 Created: 2013-02-25 Last updated: 2017-12-06Bibliographically approved

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