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Low Frequency Impact Sound in Timber Buildings: Simulations and Measurements
Linnaeus University, Faculty of Technology, Department of Mechanical Engineering. SP Technical Research Institute of Sweden. (Byggteknik)ORCID iD: 0000-0002-0019-4568
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

An increased share of construction with timber is one possible way of achieving more sustainable and energy-efficient life cycles of buildings. The main reason is that wood is a renewable material and buildings require a large amount of resources. Timber buildings taller than two storeys were prohibited in Europe until the 1990s due to fire regulations. In 1994, this prohibition was removed in Sweden.

    Some of the early multi-storey timber buildings were associated with more complaints due to impact sound than concrete buildings with the same measured impact sound class rating. Research in later years has shown that the frequency range used for rating has not been sufficiently low in order to include all the sound characteristics that are important for subjective perception of impact sound in light weight timber buildings. The AkuLite project showed that the frequency range has to be extended down to 20 Hz in order to give a good quality of the rating. This low frequency range of interest requires a need for knowledge of the sound field distribution, how to best measure the sound, how to predict the sound transmission levels and how to correlate numerical predictions with measurements.

    Here, the goal is to improve the knowledge and methodology concerning measurements and predictions of low frequency impact sound in light weight timber buildings. Impact sound fields are determined by grid measurements in rooms within timber buildings with different designs of their joist floors. The measurements are used to increase the understanding of impact sound and to benchmark different field measurement methods. By estimating transfer functions, from impact forces to vibrations and then sound pressures in receiving rooms, from vibrational test data, improved possibilities to correlate the experimental results to numerical simulations are achieved. A number of excitation devices are compared experimentally to evaluate different characteristics of the test data achieved. Further, comparisons between a timber based hybrid joist floor and a modern concrete floor are made using FE-models to evaluate how stiffness and surface mass parameters affect the impact sound transfer and the radiation.

    The measurements of sound fields show that light weight timber floors in small rooms tend to have their highest sound levels in the low frequency region, where the modes are well separated, and that the highest levels even can occur below the frequency of the first room mode of the air. In rooms with excitation from the floor above, the highest levels tend to occur at the floor levels and in the floor corners, if the excitation is made in the middle of the room above. Due to nonlinearities, the excitation levels may affect the transfer function in low frequencies which was shown in an experimental study. Surface mass and bending stiffness of floor systems are shown, by simulations, to be important for the amount of sound radiated.

    By applying a transfer function methodology, measuring the excitation forces as well as the responses, improvements of correlation analyses between measurements and simulations can be achieved

Place, publisher, year, edition, pages
Linnaeus University , 2016. , 100 p.
Series
, Faculty of Technology, Report, 46
Keyword [en]
Low-frequency, impact sound, light weight floor, timber joist floor, tapping machine, multi-storey timber building, frequency response functions.
Keyword [sv]
Stegljud
National Category
Other Civil Engineering Fluid Mechanics and Acoustics
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
URN: urn:nbn:se:lnu:diva-58068ISBN: 978-91-88357-46-5OAI: oai:DiVA.org:lnu-58068DiVA: diva2:1045835
Presentation
2016-11-30, Sal Tegner, Linnéuniversitet, hus H, Växjö, 10:00 (English)
Opponent
Supervisors
Projects
ProWoodSilent Timber BuildUrban TranquilityBioInnovation FBBB
Funder
Knowledge Foundation
Available from: 2016-11-15 Created: 2016-11-10 Last updated: 2016-11-24Bibliographically approved
List of papers
1. Low frequency measurements of impact sound performance in light weight timber frame office buildings
Open this publication in new window or tab >>Low frequency measurements of impact sound performance in light weight timber frame office buildings
2012 (English)In: Proceedings of EURONOISE 2012, European Acoustics Association, European Acoustics Association (EAA), 2012Conference paper (Refereed)
Place, publisher, year, edition, pages
European Acoustics Association (EAA), 2012
National Category
Construction Management
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-58128 (URN)
Conference
EURONOISE 2012
Available from: 2016-11-14 Created: 2016-11-14 Last updated: 2016-11-15Bibliographically approved
2. Low frequency sound pressure fields in small rooms in wooden buildings with dense and sparse joist floor spacings
Open this publication in new window or tab >>Low frequency sound pressure fields in small rooms in wooden buildings with dense and sparse joist floor spacings
2015 (English)In: Proceedings of the Internoise 2015 conference, Society of Experimental Mechanics (SEM) , 2015Conference paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
Society of Experimental Mechanics (SEM), 2015
Keyword
low frequency, sound pressure, small rooms, wooden buildings, joist floor
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-45737 (URN)2-s2.0-84947589018 (ScopusID)
Conference
Internoise, 9-12 August, 2015, San Francisco
Note

Ej belagd 20160411

Available from: 2015-08-17 Created: 2015-08-17 Last updated: 2016-11-11Bibliographically approved
3. Low Frequency Force to Sound Pressure Transfer Function Measurements Using a Modified Tapping Machine on a Light Weight Wooden Joinst Floor
Open this publication in new window or tab >>Low Frequency Force to Sound Pressure Transfer Function Measurements Using a Modified Tapping Machine on a Light Weight Wooden Joinst Floor
2016 (English)In: Proceedings of WCTE, World Conference on timber Engineering, August 22-25, 2016, Vienna, Austria, WCTE , 2016Conference paper (Other academic)
Abstract [en]

In recent years research has shown that low frequency impact sound is of significant importance for inhabitants´ perception of impact sound in buildings with light weight wooden joist floors. The tapping machine is well defined as an excitation device and is a standard tool for building acoustics. However, the excitation force spectrum generated for each individual floor is unknown when using a tapping machine. In order to increase the possibilities to compare simulations to impact sound measurements, there is a need for improvement of impact sound measurement methods. By measuring the input force spectrum by a modified tapping machine and the sound in the receiver room, transfer functions can be achieved.In the light weight wooden building used for the evaluation test of the proposed method, structural nonlinearities are evident in the frequency response functions stemming from different excitation levels. This implies that for accurate FRF-measurements in low frequencies, excitation magnitudes that are similar to these stemming from human excitations should preferably be used.

Place, publisher, year, edition, pages
WCTE, 2016
Keyword
Low-frequency impact sound, light weight wooden joist floor, tapping machine, frequency response functions
National Category
Applied Mechanics
Research subject
Technology (byts ev till Engineering), Mechanical Engineering
Identifiers
urn:nbn:se:lnu:diva-57424 (URN)
Conference
WCTE, World Conference on timber Engineering, August 22-25, 2016, Vienna, Austria
Projects
ProWood
Available from: 2016-10-17 Created: 2016-10-17 Last updated: 2016-11-15Bibliographically approved
4. Impact evaluation of a thin hybrid wood based joist floor
Open this publication in new window or tab >>Impact evaluation of a thin hybrid wood based joist floor
2016 (English)In: Proceedings of ISMA 2016, presented at the International Conference on Noise andVibration Engineering (ISMA), ISMA , 2016Conference paper (Refereed)
Abstract [en]

The purpose of this paper is twofold. The first aim is to develop a numericalanalysis procedure, by combining FRFs from FE-models with analyticalformulas for sound emission and transmission from the ceiling anddownwards within a room with four walls. The aim is to, by applying thisapproach; accomplish a tool which calculates the relative impact soundbetween different joist floors, in the low frequency range. The second aim is tobenchmark a thin hybrid wooden based joist floor with similar thickness,surface weight and global bending stiffness as a concrete hollow core floorstructure. What will be the difference in sound transmission? The question isrelevant since it may be necessary to make thinner wood based joist floors inhigh rise buildings, if wood should stay competitive against concrete. Theresults show that the direct transmissions of impact sound are very similararound the first bending mode. As the frequency increases, the modes in thestructures differ significantly. Below 100 Hz, the concrete floor has 4 modes,while the hybrid joist floor has 9 modes. As the frequency increases the soundradiation characteristics differs. The results show that it is possible to havesimilar sound transmission properties around the first bending modes for ahybrid based joist floor and a hollow core concrete floor structure with similar thicknesses. At the first modes of the structure, the information about thesurface weight and global bending stiffness are useful for prediction of soundtransmission properties but for higher modes, they are not sufficient.

Place, publisher, year, edition, pages
ISMA, 2016
National Category
Construction Management
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-58129 (URN)
Conference
The International Conference on Noise and Vibration Engineering (ISMA) in Leuven, Belgium in September 2016.
Note

Ej belagd 161115 /Viveka

Available from: 2016-11-15 Created: 2016-11-14 Last updated: 2016-11-18Bibliographically approved

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