Vibroacoustic modelling of a dowelled-joist timber floor using finite element methods


Filippoupolitis, Marios (2014) Vibroacoustic modelling of a dowelled-joist timber floor using finite element methods. Master of Philosophy thesis, University of Liverpool.

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Abstract

Timber floor systems are often used as separating floors between dwellings in multi-storey buildings as they are a sustainable, economical, lightweight solution. However, compared to concrete floors, typical timber joist floor systems tend to provide lower impact sound insulation in the low-frequency range (below 200 Hz). The research in this thesis forms part of a project funded by the Swiss National Science Foundation to develop a new dowelled-joist timber floor using Swiss hardwood with the aim of improving the impact sound insulation below 200Hz. This floor consists of dowel-connected joists that form an assembly which can then be connected to other assemblies using metal screws. It is sufficiently complex that numerical models are required to give insight into its dynamic response and its sound radiation; hence in this thesis, finite element models are developed and validated to carry out this modelling. Finite element models have been developed and validated against experimental modal analysis in terms of eigen-frequencies and mode shapes for individual beam assemblies and a complete dowelled-joist timber floor formed from three assemblies. Models of increasing complexity have been developed to find an approach that provides good agreement with experimental results. This has resulted in a model that use spring connections at the dowel positions combined with precise modelling of the boundary conditions at the two ends of the assemblies. Close agreement has been achieved between this model and results from experimental modal analysis with the differences between the eigen-frequencies in the majority of the mode pairs being less than 10 %. Close agreement has also been achieved in terms of modeshapes with MAC values greater than 80 % for the majority of the mode pairs. For sound radiation from a rectangular plate into a rectangular room, a finite element model has been developed for fluid-structure interaction. The finite element model has been validated against a normal mode model for both a 140 mm and 180 mm concrete plate. This validated approach to modelling has then been used to predict sound radiation from the dowelled-joist timber floor into a rectangular room. In order to accommodate a finite element model of the dowelled-joist floor which had ‘virtual gaps’ between the joists it was necessary to introduce a ‘transfer plate’ to transfer the motion from the dowelled-joist timber floor to the acoustic medium. This approach appears to be novel as no mention of it has been found in the literature. Use of this transfer plate was validated in terms of both vibration and sound radiation. Compared to the concrete floors the dowelled-joist floor was found to have significant sound radiation around the 16Hz band (near the lowest eigen-frequency). The work carried out in this thesis will enable future research to make a more detailed assessment of the impact sound insulation for the dowelled-joist timber floor.

Item Type: Thesis (Master of Philosophy)
Additional Information: Date: 2014-09 (completed)
Depositing User: Symplectic Admin
Date Deposited: 17 Feb 2015 10:41
Last Modified: 17 Dec 2022 01:26
DOI: 10.17638/02002602
Supervisors:
URI: https://livrepository.liverpool.ac.uk/id/eprint/2002602
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