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FE modeling of a lightweight structure with different junctions
Linnaeus University, Faculty of Science and Engineering, School of Engineering. (Byggteknik)
Linnaeus University, Faculty of Science and Engineering, School of Engineering. (Maskinteknik)ORCID iD: 0000-0002-4404-5708
SP Wood Technology, SP Technical Research Institute of Sweden. (Byggteknik)
2012 (English)In: Euronoise 2012-proceedings / [ed] Czech Acoustical Society, European Acoustics Association (EAA), 2012, 162-167 p.Conference 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. 162-167 p.
, Euronoise proceedings, ISSN 2226-5147
Keyword [en]
Lightweight structure finite element dynamic
National Category
Civil Engineering
Research subject
Technology (byts ev till Engineering), Civil engineering
URN: urn:nbn:se:lnu:diva-21194ISBN: 978-80-01-05013-2OAI: diva2:544466
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
In thesis
1. Structural-acoustic vibrations in wooden assemblies:: Experimental modal analysis and finite element modelling
Open this publication in new window or tab >>Structural-acoustic vibrations in wooden assemblies:: Experimental modal analysis and finite element modelling
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
VIBRATIONER OCH STOMBURET LJUD I TRÄKONSTRUKTIONER : Experimentell modalanalys och finit elementmodellering
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. 100 p.
Linnaeus University Dissertations, 115/2013
wooden framed structure, light weight buildings, multi-storey, flanking transmission, junction, vibration distribution, impact noise, damping, elastomers, finite element analysis, experimental modal analysis, FRF, 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
urn:nbn:se:lnu:diva-24562 (URN)978-91-87427-04-6 (ISBN)
Public defence
2013-03-15, Södrasalen, Hus M, Lückligs Plats 1, VÄXJÖ, Sweden, 14:24 (Swedish)
Available from: 2013-02-28 Created: 2013-02-25 Last updated: 2013-02-28Bibliographically approved

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