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Timber beam constructions are very common in Norwegian multifamily buildings both for vertical and horizontal partitions. The sound and vibration properties do unfortunately not fulfil expectations many people have to normal human occupancies, especially concerning lightweight timber floor constructions. For such constructions, two important challe...
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... Alternatively, the impulse may be imparted by a quick release of an attached dead weight from below the floor, a free drop[112], or from the bounce of a heavy rubber ball to simulate an adult jumping[124][133][134][135][136], as illustrated inFigure 4.2. An impulse may also be produced by a suitably sized hammer, illustrated inFigure 4.3. ...
Experimental and Finite Element Investigations of the Serviceability Behaviour of CLT Floors
... The effect of this is to lower the resonance frequency of the ceiling assembly, thereby creating an impedance mismatch. This causes incident waves to be partially reflected back into the structure [70]. Resilient ceilings have become widely used for the attenuation of vertical structure-borne sound transmission in multi-story timber buildings. ...
In recent years, advances in timber engineering, combined with an associated evolution in building codes, have led to a significant expansion of multi-storey timber construction worldwide – helping to unlock timber's potential as a sustainable alternative construction material. This expansion has intensified a long-recognised need for more effective methods to attenuate low frequency (20–120 Hz) structure-borne sound. Being lighter and less stiff than steel and concrete, timber structures tend to offer less inertial and elastic resistance to impact forces and existing sound insulation treatments provide inadequate attenuation in the 20–120 Hz range. This leads to high levels of low frequency noise transmission and deleterious effects on occupant comfort. This review lays out the fundamentals of the problem, the significance of its effects on building occupants, and the shortcomings of existing technologies developed to solve it. In this context, potential new metamaterial-based approaches are then considered. In acoustic metamaterials, previously impossible properties, such as infinite or negative mass density, stiffness, or bulk modulus, have been achieved, opening new possibilities for wave attenuation. However, practical issues, relating to structural capacity, imposed additional mass, and the breadth of attenuated frequency ranges, remain challenges to be solved. This article provides a broad overview of the characteristics that make low-frequency structure borne sound attenuation in multi-storey timber buildings so critical for occupant comfort and so difficult to achieve. It analyses the limitations of existing technologies and identifies nonlinear metamaterials that use vibro-impact oscillators to induce energy flow from low to high frequencies as having the best potential for overcoming those limitations.
... An ISO rubber ball is more similar in its excitation characteristics with regard to impedance and force in the low frequency range. The differences and similarities compared to the characteristics of a human foot excitation are shown by Homb [9] and Jeon, Ryu, Jeong and Tachibana [10], and Gover, Bradley Schoenwald and Zeitler [11]. ...
... Due to the potential non-linearities in transmissions, it would be beneficial to be able to measure the impact force of an ISO rubber ball to form FRFs by combining the force with responses, i.e. sound pressure measured with microphones in the receiving room. There are potentially different methods for measuring the force from the rubber ball, see for instance Homb [9] and Robinson and Hopkins [15]. Important aspects when designing the test rig used in the present study were that it should be suitable to carry in field measurements (i.e. ...
... Also, the force spectra generated by the rubber ball have not been fully analyzed with regard to how large the variations may be based on the variations in different floors. The influence of different floor designs has mainly been studied by the maximum amplitudes of the rubber ball's force signals, see Homb [9]. Here, the objective is to measure and analyze the ISO rubber ball's force spectra at low frequencies in relation to dif-ferent floor properties. ...
Impact sound performance below 100 Hz forms part of a design criterion that is particularly important for multi-story timber buildings. An ISO tapping machine, which is predominantly used for impact sound measurement, has properties that may result in less measurement accuracy in the low frequency range, down to 20 Hz, than in its traditional measurement range above 100 Hz. The characteristics of the pistons’ impact are dissimilar to the impact of a human foot in this lower range. This may cause low signal-to-noise ratios in field measurements and the test data may also be less representative due to the test objects’ possible structural nonlinearities affecting impact sound transmission. The ISO rubber ball has shown to bear a close resemblance to a human’s excitation in the low frequency range, which makes it a suitable excitation device from this perspective. To support correlations between simulations and measurements, measuring impact forces in order to extract frequency response functions would be beneficial. To enable measurements of impact forces that stem from the ISO rubber ball, equipment for field measurements of forces and potentially point mobilities has been manufactured and evaluated. Furthermore, an investigation has been conducted into the repeatability of the rubber ball’s low frequency force spectrum for floors with different mobilities. Impact force measurements have been made on lightweight timber floors as well as on concrete floors. Within the frequency range up to around 55 Hz, it appears to be possible to use a prescribed force spectrum for the ISO ball, together with impact sound measurements, to create accurate impact force to sound frequency response functions for different floors. Also, instrumenting the impact point with an accelerometer enables estimates to be made of direct point mobilities.
... Homb 14 shows a significant difference in measured structural accelerance (acceleration/force) through floors depending on whether the excitation was made directly above a structural joist, or between joists. That study shows differences of 10-20 dB on some of the tested designs with joists having distances of 60 cm. ...
Traditionally, product development concerning acoustics in the building industry is measurement oriented. For lightweight floors, frequencies that are lower than the frequency range for heavy concrete floors are an issue. The frequency range of from 50 Hz down to 20 Hz influences the human perception of impact sound in multi-story apartment buildings with lightweight floor constructions, such as timber floors, for example. It is well known that a lower frequency range of interest makes finite element simulations more feasible. Strategies for reducing impact sound tend to be less straightforward for timber floors because they have a larger variation of designs when compared to concrete floors. This implies that reliable finite element simulations of impact sound can save time and money for the building industry. This study researches the impact sound transmission of lightweight timber floors. Frequency response functions, from forces on excitation points to sound pressure in the receiving cavity below, are calculated. By using fluid elements connected to reflection-free boundary elements under the floors in the models, the transmission and insulation can be studied without involving reverberation. A floor model with a hard screed surface will have a larger impact force than a softer floor, although this issue seems less pronounced at the lowest frequencies. To characterize floor surfaces, the point mobilities of the impact points are also calculated and presented. The vibration and sound transmission levels are dependent on the selection of the excitation points.
... Bahadori-Jahromi et al. [9,10] innovated timber floors with multiwebbed joists and conducted static and dynamic tests on these floors. Homb [11] assessed human perception based on the results of impact-induced low frequency vibrations on timber floors. ...
Based on classic vibrational bending theory on beams, this paper provides comprehensive analytical formulae for dynamic characteristics of two equal span continuous timber flooring systems, including frequency equations, modal frequencies, and modal shapes. Four practical boundary conditions are considered for end supports, including free, sliding, pinned, and fixed boundaries, and a total of sixteen combinations of flooring systems are created. The deductions of analytical formulae are also expanded to two unequal span continuous flooring systems with pinned end supports, and empirical equations for obtaining the fundamental frequency are proposed. The acquired analytical equations for vibrational characteristics can be applied for practical design of two-span continuous flooring systems. Two practical design examples are provided as well.
... The needed numbers of measurements to fulfill the standard uncertainty of the average values of ISO 12999-1:2014 are presented. The values within the brackets are the calculated numbers of measurements required according to Eqn.(9).SE 5 , the standard error for the average of five microphones N M , number of required sets of five microphones to fulfill ISO 12999 ...
Low-frequency impact sound insulation, down to 20 Hz, has a significant effect on humans' dissatisfaction due to noise in timber buildings. Today, the low-frequency procedure of the ISO 16283-2:2015 impact sound measurement standard covers the frequency range down to 50 Hz for the use of an ISO tapping machine, but does not yet cover the use of an ISO rubber ball. Here, microphone grid measurements were made in two small rooms that were excited by an ISO rubber ball from the rooms above. In each grid, 936 microphone positions were used to capture data representing the full spatial fields of impact sound pressures from 10 to 500 Hz for one excitation location for each room. The data show that the positions at the radiating ceiling surfaces have low maximum sound pressure levels compared to the pressure levels at the floors, especially in the floor corners. First, a measurement procedure to predict the maximum exposure of low-frequency sound in a room is proposed It is suggested that the maximum values for each frequency band in the corners opposite to the partition being excited (i.e., the floor corners) be used. Second, a procedure to predict the room average sound pressure level and the prediction's normal distribution is suggested. Iterative measurements with random microphone locations and random excitation locations are used. The advantage of this method is that the required precision and information about the sensitivity due to different excitation points are obtained. © 2018 Institute of Noise Control Engineering. All rights reserved.
... Many residents in multi-storey wood buildings perceive structureborne sound as being annoying, even though the buildings may fulfil regulations regarding sound insulation. This issue has been given much attention by researchers during the last decades, and the low-frequency sound transmission has been pointed out as the main reason behind the complaints [1][2][3][4][5][6][7][8]. In [8], the impact sound insulation in eight wood buildings was measured according to standardised procedures. ...
The main challenge in predicting structure-borne sound in wood buildings is to accurately model the vibration transmission between the source and the receiving room. Large variations in model parameters make it difficult to predict absolute vibration levels and to make conclusions regarding the relative effects of different designs. A step towards establishing reliable models is to investigate the possibilities and limitations of using deterministic methods, which requires correlations between simulations and measurements. In this paper, we present a multi-level model correlation approach for low-frequency vibration transmission in wood buildings. We apply the proposed approach to a scaled-size experimental structure representing a part of a two-storey wood building, and we evaluate the results for frequencies up to 100 Hz. We perform correlations between simulations and measurements four different levels: structural components (viz. beams and boards), planar structures (viz. floor, ceiling and walls), room structures and the complete structure. The results indicate that the dynamic behaviour of the experimental structure was to a great extent captured by the developed model. Based on the observations made in the multi-level correlations, we discuss important model parameters and propose modelling guidelines. We conclude that it is possible to employ deterministic methods in order to simulate the low-frequency vibration transmission in wood buildings provided that measurement data for calibration purposes are available. The developed numerical model can be used as a reference model for investigations on the effects of variations and uncertainties in the modelling.
... [23,[28][29][30][31][32][33]. The cited studies consider the vibration transmission since it is a step towards enabling the prediction of low-frequency structure-borne sound, which has been shown to be a major source of annoyance to residents in wood buildings [24][25][26][27]. There is no clear definition of what is the low-frequency range, but for structure-borne sound in buildings it is often referred to as frequencies below 100 or 200 Hz. ...
Dynamic substructuring is often employed to reduce the size of numerical models for structural dynamic analysis. In this paper, we discuss how elastomeric vibration isolators can be modelled within the framework of dynamic substructuring in order to obtain accurate and efficient reduced order models. For several reasons, it is beneficial to divide a structure containing elastomeric isolators into substructures at the interfaces between elastomers and surrounding parts of the structure. Therefore, we consider the elastomeric isolators as reduced coupling elements in the connections of substructure models. The coupling elements are established by reducing the number of degrees of freedom of 3D finite element models of elastomers. The main purpose of the studies presented in the paper is to evaluate the performance of different reduction method when applied to elastomer models. In addition, the effects of modelling features such as rotational coupling and frequency-dependent material properties of elastomeric isolators are investigated. A model of a wooden building structure with elastomeric isolators is used as an example case, considering steady-state dynamic analysis in the low-frequency range. The results and discussions presented in the paper provide guidance for reduced order modelling of elastomeric isolators in dynamic substructuring.
... Smith [12] systematically summarised the serviceability aspects for vibrations of timber floors, including human perception of motion, floor response to dynamic loading, avoidance of vibration problems and prediction of floor vibration. Homb [13] investigated low frequency sound and vibrations from impacts on timber floors using spectrum analysis and evaluated floor vibration perception to impacts. Ljunggren [14] explored the vibration performance of lightweight steel framed floors with various supports, top layers, ceiling joists and partitions, and evaluated the interactions between the dynamic properties of the floor and human vibration perception. ...
... Experimentally determined damping ratios are influenced by the method of testing, by the extraction method that mines modal response parameters from test data, and the boundary conditions set for data processing and modal parameter estimation. Studies based on on-site measurements of floor responses have shown damping to be significantly higher than under laboratory conditions, with values of up to 6 % (Ohlsson 1982;Homb 2006;Toratti and Talja 2006;Jarnero 2014). In older studies, test methods and parameter extraction techniques differed from those employed in modern tests, reflecting improvements in both test equipment and data analysis methods. ...
Vibration serviceability of timber floors is becoming increasingly relevant due to their increased long-span applications in pure timber and hybrid structures. As a serviceability limit state, the check of acceptable floor vibrations is part of some current timber design standards. However, a universal agreement on acceptance levels and design procedures has not been achieved. This paper gives an overview of traditional and recent design approaches for floor vibrations, with those approaches intended to allow engineers to implement design strategies that produce floors that perform acceptably under service conditions. The subsequent discussion does not catalogue all relevant technical literature, information in design manuals and aids, nor list all relevant design code rules related to vibration serviceability of timber floors. Instead what is written is intended to convey and critique the state of background knowledge, design recommendation and code rules using illustrative examples from the literature. The objective is to contribute to resolution of debate about control of floor response characteristics by engineering design methods.
