Juan Negreira

Characterisation of an Elastomer for Noise and Vibration Insulation in Lightweight Timber Buildings

Regulations regarding impact and airborne sound insulation for lightweight timber constructions have become increasingly stringent due in particular to complaints by inhabitants. Accordingly, some building techniques frequently use elastomers at junctions so as to reduce low frequency noise. Development of accurate predictive tools (involving exact material properties) by using numerical methods such as the finite element (FE) method is needed in tackling flanking transmission problems during the design phase of buildings. The present research concerns the characterisation of an elastomer, presenting an accurate method for extracting its material properties from the manufacturers data sheet (properties there being often linked to such structural effects as shape factors and boundary conditions of samples and tests). The properties were extracted by comparing results obtained by analytical calculations, FE simulations, and mechanical testing, separating geometry and material dependence and ultimately serving as input to commercial FE software for setting up the aforementioned prediction tools.

Reflection and transmission properties of a wall-floor building element: comparison between finite element model and experimental data

Lightweight structures made of timber material have a number of advantages; they may become cost effective in the future and they demand relatively short production duration. However, one of the main drawbacks is related to the sound transmission, as it is becoming an increasing nuisance. The differences in weight, stiffness, density and repartition compared to traditional materials have repercussions on how the sound propagates through the structures and problems of sound insulation in the low frequency range through the junctions may arise. This paper provides an investigation of the reflection and transmission properties of a wall-floor real-sized timber element, which resembles a section of a lightweight building. The latter investigation was carried out by comparing finite element simulations with experimental data. The fairly good match between the experimental results and the simulations point out at the applicability of the finite element analysis as a prediction tool during the design phase before buildings are actually put up in order to prevent future problems. (Less)

Predicting structure-borne sound from railway traffic

Since noise exposure can disturb the well-being, acoustical comfort in the built environment is of great importance when constructing new dwellings. Population growth causes densification of cities, which together with space limitation issues, lead to buildings being constructed closer to existing vibration sources such as motorways and railways, and vice versa. Likewise, architectural trends, environmental benefits and cost result in increased use of lighter materials such as wood and hollow-core concrete slabs. Lightweight structures make the achievement of acoustical comfort in dwellings an increasing challenge. A major issue when designing buildings regarded as acoustically pleasant, especially in the low-frequency range, is the lack of reliable prediction models to be used during the design stage of the building. Predictions of structure-borne noise are nowadays mostly made based on measurements performed on existing buildings and engineers’ experience. Hence, it is of interest to develop tools that ...

Algebraic reflections in geometric acoustics

Stochastic Ray tracing is one of the most widely used geometric acoustic algorithms, and excels primarily for modelling the late room response in high frequencies. A significant bottleneck of the algorithm is the high computational cost of testing rays for intersection with geometry, and the high amount of rays required for convergence. Several methods exist to reduce this cost by means of reducing geometric complexity. This paper instead proposes using bidirectional reflectance distribution functions (BRDF) to algebraically compute transmission paths between receivers and sources, thereby decreasing the amount of total rays needed. For each ray-geometry intersection, transmissions paths are calculated recursively, and several transmission paths can thereby be taken into account for each intersection test, while allowing for point-like transmitters and receivers. The method has been implemented on a graphics processor, and calculated room acoustic parameters are comparable to commercial geometric acoustic...

Numerical Prediction Tools for Low-Frequency Sound Insulation in Lightweight Buildings

Lightweight wooden-framed constructions have steadily increased their market share in Sweden during the last two decades. Achieving acoustic and vibration comfort in wooden-based buildings is, however, still a challenging task. Wood is high in both strength and stiffness in relation to its weight, but its variability has repercussions on how sound propagates, this triggering sound insulation problems. Even if buildings comply with present-to-day regulations, complaints amid residents often arise due to low frequency noise, as it is outside the scope of the standards (where no analyses are performed below 50 Hz). In this investigation, laboratory acoustic sound insulation measurements carried out on a facade element according to the current standards, are intended to be reproduced and calibrated by means of the finite element method. In doing so, the first steps of a numerical predictive tool mimicking the real specimen, from 0 to 100 Hz, are presented. This will enable further research about phenomena occurring in the far low end of the frequency range, which is believed to be the cause of most nuisances reported by residents. Reliable predictive tools for addressing acoustic issues during the design phase avoid additional costs of building test prototypes and ensure a better acoustic performance. (Less)

Modeling acoustic properties of different types of lightweight T-junctions

To accurately model the effect on the dynamic behavior of a floor when using glue in the joints between the chipboards and beams in a lightweight structure can be a daunting task. It is however important to have a model that can simulate these junctions with high fidelity. The behavior of T-junctions with different geometries and methods of adhesion has been previously investigated via measurements [1]. This investigation builds on that work and aims at developing an accurate finite element model of the junctions. The previously investigated junctions were made of chipboards fixed to a spruce beam using screws or a combination of screws and glue. The boards were either a single plate or two plates meeting each other on top of the beam. In this investigation different approaches of simulating the junction using the finite element method were tried. The validity of the FE models was evaluated by calibrating them with previous performed measurements in [1]. A parameter study was also performed on the models to investigate the effect of the glue on the overall performance of the structure. (Less)