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Within the scope of the recently finished cooperate research project "VibWood" at Technical University of Munich and Rosenheim University of Applied Sciences, fully parametrized numerical models for lightweight wooden floor constructions have been developed and calibrated by experimental modal analyses.
Based on a vast parametric study including floating floors and suspended ceilings a database of narrowband sound power levels in the frequency range up to 125 Hz for a wide range of floor dimensions has been set up.
A procedure will be presented on how to process the numerical data and derive single number values that allow a comparison to the standardized rating of impact sound insulation according to DIN EN ISO 717-2.
The derived data is implemented into a graphical user interface (GUI). This GUI is available for free. The database is open for additional geometries and will be enhanced by different constructions in the near future.
Competitive wooden floor systems - multi-objective optimization based on acoustics improvement
(2013)
The objective of this research project is the design of lightweight timber floor systems which have similar thicknesses to those of concrete floors but which perform better than concrete in terms of their environmental life cycle impact and in terms of airborne and impact sound insulation.
The availability of superior lightweight acoustic designs will increase the share of timber based floors within the Swiss construction market and will contribute to higher wood utilization in general.
A program for systematically developing validated finite element models for the development of lightweight timber floor systems has been proposed.
The use of Swiss hardwoods in floor systems will be studied and implemented where possible. Keywords: lightweight timber, sound transmission, impact noise
Measured transmission functions from structure-borne sound sources in a timber-frame construction
(2015)
The aim of prEN 15657-2 is to provide engineering methods to estimate the structure-borne sound power input from machinery in situations where the source mobility matches or is lower than the receiver mobility. This situation often affects lightweight constructions such as timber-frame buildings. To estimate the sound pressure level in a room that is adjacent or distant from the room containing the source, the installed structure-borne sound power has to be propagated across at least one junction in the timber-frame construction. However, at present there are no generic, validated calculation models due to the complexity and the large variety of timber-frame constructions. A simplified approach to investigate and compare the structure-borne sound transmission is to treat the framed construction as a black box and only consider one parameter, a transmission function which is the ratio of the sound pressure level in the receiving room to the injected structure-borne sound power level. To get information about the variation of this transmission function in different timber-frame constructions, measurements were made in both the laboratory and the field. Experimental results are presented showing the variation due to different building configurations and the effect of the excitation position on the transmission function.
It is common for timber ceiling constructions to include a suspended ceilings made of plasterboard. In order to minimize the radiation from impact excitation, especially in the low frequency range below 100 Hz, a detailed analysis of the vibration behaviour was necessary.
An experimental modal analysis was carried out and the radiated sound power from the suspended ceiling was measured using a sweep sine excitation by a shaker connected to the top layer of the timber floor construction.
Since the experimental modal analysis was conducted using a high frequency resolution and with a non-stationary sound field, it was necessary to check the validity of the intensity measurements by comparing it with 1/3-octave band measurements. The results show very good agreement.
By this means the radiation efficiency can be measured simultaneously with an experimental modal analysis of a structure.
A trend towards lightweight structures, e.g. timber structures, is noticeable in civil engineering, which implies the necessity to predict vibroacoustic characteristics like the transmission of structure-borne sound in order to fulfil requirements regarding serviceability. This contribution focuses on the investigation of junctions of building components e.g. between wall and ceiling. It is part of a joint research project with the aim to catalogue the coupling for a variety of junctions. The resulting database may serve to predict the transmission of structure-borne sound which is typically carried out either using a Finite Element (FEM) approach, suitable for the low frequency range, or by means of energy methods like the Statistical Energy Analysis (SEA) for the high frequency range. Therefore the so-called mid frequency gap emerges, which is examined and attempted to be closed. In this context SEA-averaging techniques are applied in the postprocessing of FEM calculations to obtain an adapted “SEAlike” approach. By varying the subsystems to be excited it is possible to determine Energy Influence Coefficients (EIC), which describe the specific energy content of the different subsystems with respect to the input power. Using this hybrid approach vibroacoustic predictions can be performed also in the mid frequency range. Inverting the EIC-matrix Coupling Loss Factors as well as Damping Loss Factors of the different subsystems can be calculated if the subsystem definition fulfils the SEA-requirements. The application of the method in combination to a classical SEA calculation and to laboratory measurements is presented.
Numerical models for the prediction of vibroacoustical characteristics of light-weighted ceilings
(2013)
In order to set up guidelines for the design of light-weighted ceilings for timber constructions to be used by engineers in practice, investigations based on both measurements and numerical models have been carried out within the cooperative research project “VibWood”.
In this contribution the setup and the calibration of the numerical model of the structure as well as the prediction of radiated sound are discussed, where a special focus is set on a dimensionless description in order to deduce information for a wide range of system’s specifications.
The structure, consisting of a timber slab, a floating floor and a suspended ceiling, is built up in a Finite Element model, where the material properties of wood and the characteristics of the system (e.g.support conditions, contact phenomena dynamic properties of individual parts) are considered.
The model is parameterized in order to enable computations with varying geometry and material parameters.
After calibrating the FE-model with the help of measurements using model updating techniques dimensionless parameters are defined based on the Buckingham-π- Theorem and computations are carried out in order to specify guidelines for various systems. The radiation of sound is computed in a post processing using Integral Transform Methods.
To ensure that building regulations are satisfied, the sound pressure level due to machinery has to be predicted at the design stage of a new building.
With the increasing popularity of multistory timber dwellings, prediction becomes an important issue for designers and consultants. At present previous project experience is often used when considering the design of wall and floor constructions and the mounting positions for machinery.
Simple tools to calculate the sound pressure levels in rooms based on machinery data and construction details are not currently available.
The approach involves two stages: firstly the description of the source and secondly the prediction of vibration transmission across the building and sound radiation into the rooms.
In this paper a simple empirical model is proposed for the second stage. This approach is based on measured transmission functions that are defined as the average sound pressure level in a receiving room relative to the injected structure-borne sound power.
This is a logical extension of approaches to characterize structure-borne sound sources that also use a power based descriptor (e.g. prEN15657:2016-02: Acoustic properties of building elements and of buildings - Laboratory measurement of structure-borne sound from building service equipment for all installation conditions) and provides a simple method to estimate the sound pressure level in a room.