Search

Recent research has been developed by different groups towards the development of sonic crystals as noise barriers. The present paper aims to contribute to this research, focusing on the possible application of this technology in practice, and exploring some aspects that may be useful for its further development. One of the objectives of this work is to explore the differences between experimental results obtained under laboratory conditions and numerical results computed with the finite element method (FEM), in 2D and 3D, understanding if different types of simplified models can be of use in the practical analysis of sonic crystals. Through this comparison, a validation of the prediction numerical models is performed, giving confidence for their use in the development and study of sonic crystal configurations. In this context, different geometric arrangements of the sonic crystals’ scatterers (the individual elements that make up the barriers) have been analyzed with the help of the numerical method, evaluating their behavior in different arrangements of numbers of elements, shape and size. A number of parametric studies are also performed introducing some randomness in the structure (in scatterer size and spacing), and analyzing its effect on the insertion loss provided by the sonic crystal. These contributions can be significantly useful for the development of new solutions, giving important hints about the sensitivity of these structures to possible defects or limitations in their production.

Prediction of vibrations in buildings due to railway traffic is challenging due to several aspects, namely the huge dimensions of the domain, the interaction between different systems, and the uncertainties inherent to the complexity of the system. Therefore, experimental/numerical hybrid prediction techniques are of great interest since they take advantage of the combination between experimental data and numerical resources. In this context, the type of foundations of a building are preponderant in the dynamic soil-structure interaction effect and may have an influence on the accuracy of the hybrid prediction. The presence of the building foundations could significantly modify the response of the local sub-soil of the building. This fact makes that the prediction of vibrations in buildings becomes a complex wave propagation problem. As different types of foundations behave differently, they lead to different dynamic responses in the structure for a prescribed incident wave field. Therefore, dynamic soil-structure interaction coupling is also affected by the building’s foundation type. In order to investigate this phenomenon, this paper studies the influence that the consideration of three different foundation typologies, shallow, slab and deep foundations, have on the prediction of railway-induced vibrations on a building using an experimental/numerical hybrid methodology. A comparison is made between the results obtained through the hybrid method and the numerical results obtained through a numerical model based on the full system

Understanding urban noise as a serious environmental problem in urban centers, the development and application of noise control strategies have demanded a recent effort by several researches. In this case, the development of acoustic metamaterial artificially designed to manipulate the wave phenomena has become a recent topic, aiming at optimized responses, and enables the development of subwavelength devices with potential application in passive ventilation and noise mitigation, providing better environmental conditions in buildings. The present paper intends to contribute to the knowledge in this field by investigating the concept of an acoustic metamaterial with negative bulk modulus based in a parallel arrangement of Helmholtz Resonators. Experimental and numerical investigations are carried out to determine the acoustic potential of the proposed meta structure in terms of sound absorption and sound transmission loss. The developed concept exhibits significant benefits in the properties of sound transmission loss, and seems a potential application for noise control at specific frequency bands (mainly at low to middle frequency) in building façades.

A sandwich wall-panel solution based on Cross-Laminated Timber (CLT) has been recently developed aiming to rationalize the wood volume and combine it with a low-density core layer for improved thermal insulation and reduced weight. Such panel, named Cross-Insulated Timber (CIT), was previously optimized to fulfil structural and thermal requirements with a minimum production cost. The layout of the new panel is similar to the one of a five-layer CLT panel, but the inner layer is made of polyurethane rigid foam instead of timber. Besides its technical and economical benefit, it is also of interest to assess its environmental impact. This paper presents a study about the environmental impact assessment through Life-Cycle Analysis (LCA) of this new type of wood-based sandwich wall panel. A cradle-to-gate LCA with consideration of different end-of-life scenarios is performed in order to identify the processes that contribute the most to the environmental impact of the CIT panel solution proposed during its life cycle, namely during manufacturing. The LCA includes also the comparative assessment of: (i) varying the thickness of the wood layers, with respect to the optimized CIT panel; (ii) using an alternative core material, namely insulation cork board (ICB), and (iii) applying structurally equivalent three-layered CLT solutions, with alternative core materials. The results obtained show that the manufacturing process of the CIT panel, namely the polyurethane foam production and the press and curing processes during the panels assembly are the ones that produce the highest impacts. It was also found out that varying the thickness of the wood layers compared to the optimized solution leads, in general, to an increase in all impact categories. This means that the optimized solution in terms of economic costs is also the one which presents the lowest environmental impacts. Compared to equivalent CIT panels with ICB core and CLT solutions, the environmental performance of the panel proposed was better for some impact categories, while it was worse in others.

In this paper, we propose two adaptive semi-explicit/explicit numerical approaches to analyse nonlinear porodynamic models. In this context, simple, stabilised, non-iterative, reduced effort, decoupled formulations are developed, in which the time integrators of the time marching procedures are locally defined, allowing distinct values to be assigned to each element of the spatial discretisation. Thus, linked formulations between the adopted temporal and spatial solution procedures take place, allowing the time marching techniques to adapt to the properties of the discretised model properly and locally. For each technique, each phase of the coupled problem is treated separately, uncoupling the governing equations of the porous model. Therefore, simpler, smaller and better-conditioned systems of equations are obtained, which can be handled without considering any iterative computation, even when nonlinear models are regarded. Additionally, reduced systems of equations may arise for each phase of the model, which may then be analysed without considering stability restrictions for their time solutions. Also, incompressible and impermeable media may be directly analysed, without requiring any special discretisation procedure, as is the case in standard solution techniques. At the end of the manuscript, numerical examples are presented, illustrating the effectiveness of the proposed new formulations.

A novel experimental/numerical hybrid methodology for the assessment of railway-induced ground-borne vibration in buildings based on experimental measurements in the soil surface is proposed in this paper. This methodology has been specifically designed for the prediction of railway-induced vibration in buildings to be constructed close to an operative railway infrastructure, although it can be applied for other types of vibration sources. The model of the incident wave field induced by the railway infrastructure consists of a set of virtual forces applied in the soil, which would be obtained from vibration experimental measurements in the surface of the ground where the building will be constructed. These virtual forces can be subsequently applied to a model of the building-soil system to obtain a prediction of the vibration levels that will be induced by the existing railway infrastructure to the studied building. In the present work, this methodology is theoretically defined and it is numerically validated for two-dimensional and two-and-a-half-dimensional cases. To numerically test the methodology, the measured ground surface responses are replaced by simulated ones obtained in a set of points called collocation points. In this context, a parametric study has been developed with the aim of finding out a robust criterion for the application of the present methodology with respect to the amount and location of the collocation points (representing vibration sensors) and virtual forces. It is found that the distance between virtual sources should be smaller than the S-wave wavelength of the upper soil layer corresponding to the highest frequency of the frequency range of interest to ensure the reliability of the methodology. Moreover, the proposed method is found to be insignificantly affected by the building-tunnel dynamic coupling for building-tunnel distances above 20 m. The proposed hybrid model would simplify the usual numerical prediction approach commonly adopted for dealing in detail with these problems, since a model of the railway infrastructure is no longer required. Moreover, it would reduce the uncertainty of the prediction due to the use of experimental measurements of the particular site to be studied. In addition, it would provide a higher accuracy and flexibility than empirical models based on experimental transmissibility functions between the soil surface and the building This work was financially supported by: • Base Funding - UIDB/04708/2020 and Programmatic Funding - UIDP/04708/2020 of the CONSTRUCT - Instituto de I&D em Estruturas e Construç˜oes - funded by national funds through the FCT/MCTES (PIDDAC) and by “Institute for sustainability and innovation in structural engineering” - ISISE (UIDP/04029/2020), funded by the Fundaç˜ao para a Ciˆencia e a Tecnologia (FCT), I.P., and Regional Operational Programme CENTRO2020 within the scope of project CENTRO-01- 0145-FEDER-000006. • The project NVTRail: Noise and Vibrations induced by railway traffic in tunnels: an integrated approach, funded by FEDER funds through COMPETE2020 and by national funds (PIDDAC) through FCT/ MCTES, with grant reference POCI-01-0145-FEDER-029577. • The project VIBWAY: Fast computational tool for railway-induced vibrations and re-radiated noise assessment, with reference RTI2018- 096819-B-I00, supported by the Ministerio de Ciencia e Innovación, Retos de Investigación 2018. This work was partially carried out under the framework of In2Track2, a research project of Shift2Rail (H2020). The financial support provided by University of Leeds Cheney Award Scheme is also appreciated

The prediction of the sound absorption coefficient in diffuse field conditions is of great interest to an acoustic project. Foams and granular materials like porous concrete have been used in many internal or external applications as sound absorbers. However, many doubts have regularly been discussed in scientific literature. The simple use of experimental impedance tube methods, that consider only the incident acoustic plane waves, is not equivalent to the experimental measurement in a reverberant room, which is necessary for a correct characterization of a given constructive solution. The scientific community has explored several methods to predict and approximate the sound absorption coefficient in diffuse field conditions, using only acoustic plane wave data. However, many of them do not allow a realistic approximation of the reverberant room measured data. Therefore, two numerical models are herein proposed which consider the porous media on the fluid-equivalent theory, first, a two-dimensional (2D) finite element method, and, second, a three-dimensional (3D) boundary element method (BEM). These methods are compared with analytical equations and experimental data from the reverberant room, studying the influence of the porous material panel size in the sound absorption coefficient in diffuse field conditions. To illustrate the proposed method’s practical interest, the BEM 3D model was used to determine the diffuse field’s sound absorption coefficient for finite-sized panels of porous concrete. This test was done for plane panels and for slit-like surfaces to highlight the possibilities of the proposed method. This work has been financed by national funds through FCT – Foundation for Science and Technology, I.P., within the scope of the R&D unit Institute for Sustainability and Innovation in Structural Engineering – ISISE (UIDP/04029/2020) and through the Regional Operational Programme CENTRO2020 within the scope of the project CENTRO-01-0145-FEDER-000006. This work was developed within the scope of the POCI-01-0247- FEDER-033990 (iNBRail) Project, funded by FEDER funds through COMPETE 2020, Portugal 2020. The authors also acknowledge COST Action DENORMS CA15125, supported by COST (European Cooperation in Science and Technology).

The development of advanced numerical techniques such as eXtended/Generalized Finite Elements Methods (XFEM/GFEM) has provided means for accurate prediction of material failure. However, the present theories mostly rely on a global formulation, where the system of equations is subject to progressive dimension increase with crack evolution. In this regard, an independent multilayered enrichment is proposed for the XFEM/GFEM family of methods where a few elements in close proximity are assigned to an enrichment layer independent of the remaining ones. The enhanced degrees of freedom can be condensed out at the layer level, which leads to system dimensions, sparsity, and bandness identical to those of the underlying finite elements. Nodal and elemental enrichment methods are shown to be particular limit cases of present approach. The robustness of the proposed approach is first demonstrated in element-level examples. The use of only few adjacent elements in a group enrichment is shown to suffice for acceptable results while the order of the condition number of the final stiffness matrix resembles the underlying uncracked finite element counterpart. Finally, using several structural examples, the accuracy and robustness of the method is shown in terms of force–displacement response, stress fields, and traction continuity in nonlinear problems.

This paper presents an experimental study about the bonding quality of Maritime pine (Pinus pinaster Ait.) cross-layered wood elements glued with one-component polyurethane adhesive. The experiments comprised shear and delamination tests according to standard EN 16351 focusing on the influence of the following parameters: bonding pressure, adhesive spread rate, pre-treatment with primer and layer thickness. The results obtained show that increasing bonding pressure increases significantly the wood failure percentage after delamination or shear tests, while the delamination and the shear strength are not significantly affected. Moreover, it was found that the use of primer enhances significantly the bonding quality; nevertheless, EN 16351 requirements are fulfilled even for the lower bonding pressure and adhesive spread rate recommended by the manufacturer of the adhesive used in the experiments. The layer thickness, for the tested range, had no influence on the delamination and shear results and limited one on the wood failure percentage after shear or delamination tests. No relevant influence was found for the adhesive spread rate. In the experiments the combination of gluing Maritime pine with Australian blackwood (Acacia melanoxylon R.Br.) was also investigated and, for this combination, the standard requirements were successfully fulfilled.

Noise abatement provided by acoustic metamaterials is one of the peculiar features presented by these remarkable materials. In fact, the use of local resonant elements and their periodic distribution in the form of so-called sonic crystal arrangements have demonstrated to enhance those attenuation properties. In this work, the authors present an efficient three-dimensional (3D) numerical model based on the Boundary Element Method (BEM) to analyse the acoustic behaviour in the frequency domain of finite periodic arrays of acoustic resonators. Unlike most analytical methods, the proposed model captures the finite features of these systems and their associated effects. Furthermore, usual numerical tools such as the Finite Element Method (FEM) may become impractical because the detailed and complex geometry of these devices would lead to very large discretized spatial domains. Instead, in the proposed model, only the resonators have to be discretized. Actually, an efficient strategy has been devised to adequately take into account the periodicity of the finite array of resonators, resulting in significant savings of computational resources. Additionally, the Adaptive Cross Approximation (ACA) technique is used, further reducing the computational requirements since it is based on hierarchical representation of matrices and allows a very efficient storage of the system matrix. This work has been framed within POCI-01-0247-FEDER-017759 (SmartCore) and POCI-01-0247-FEDER-033691 (HLS - Hybrid Log Shield) Projects, funded by the COMPETE 2020, Portugal 2020 and FEDER funds. This work was partly financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT – Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007633 and through the Regional Operational Programme CENTRO2020 within the scope of the project CENTRO-01-0145-FEDER-000006. This work was also developed in the scope of COST (European Cooperation in Science and Technology) through the COST Action CA15125 – DENORMS: “Designs for Noise Reducing Materials and Structures” and the EU funding support is here acknowledged.

The interest of scientific and technical communities in the re-radiated noise phenomenon has been increasing over the last years, motivated by complaints of inhabitants living in buildings located next to sources of vibrations. The study and quantification of low-frequency noise levels inside these buildings demand accurate methods of prediction. Thus, the present paper aims to contribute to the listed goal by presenting an experimental validation of a 3D FEM-MFS hybrid numerical model, where the Finite Element Method (FEM) is used to evaluate the structural response and the Method of Fundamental Solutions (MFS) is adopted to assess the acoustic response inside a closed space. The experimental work carried out consisted in the excitation of a reduced-size acoustic chamber by applying an impulse load induced by an instrumented hammer. The structural and acoustic dynamic responses of the system were simultaneously monitored by a set of accelerometers and microphones. The case study was then modelled and the experimental data compared with the numerical results, showing that the numerical approach used is efficient and accurate, as it correctly addresses realistic situations involving re-radiated noise by elastic structures.

The topic of vibrations induced by rail traffic has received a special attention from the scientific community over the last decades, which is justified by the increase of health awareness and comfort demands by the communities living nearby such infrastructures. Regarding mitigation of sound waves propagation, innovative solutions based on the phononic crystals concept have been extensively studied in recent years and their capability to attenuate wave propagation at specific frequency bands is well known. However, the extension of this concept to shield sensitive buildings from elastic waves propagation induced by traffic and by other human activities is not completely understood due to the lack of studies in this topic. Therefore, the present paper aims to give a contribution on the analysis of the vibration attenuation that can be provided by buried periodic structures when applied parallel to railway tracks. To achieve this goal, a numerical approach is followed with a 2.5D finite element method combined with perfectly matched layers (FEM-PML) model, previously developed by the authors, being applied in order to obtain a deeper understanding about the attenuation effects that can be provided by arrays of periodic buried inclusions. A step-by-step study is carried out to get an accurate insight about the phenomena involved, allowing the derivation of theoretical expressions and simplified rules that can be useful for the design of vibration mitigation solutions based on this concept.

[EN] The method of fundamental solutions has been applied to evaluate the influence of fish models geometrical features on the target strength (TS) directivity and TS frequency response of swimbladdered fish. Simplified models were considered for two fish species: gilt-head sea bream (Sparus aurata, Linnaeus 1758) and Atlantic salmon (Salmo salar, Linnaeus 1758), and different geometrical details of their morphology were studied, such as backbone presence, and its curvature or the inclusion of vertebrae modulation. Swimbladder shape and tilt, together with the inclusion of backbone (and its realistic curvature) for dorsal measurements were the most important features for proper estimation of mean TS. The estimation of mean TS is considered including the effect of fish tilt, the echosounder frequency, and the fish-to-transducer distance., This work received funding from ACUSTUNA project ref. CTM2015-70446-R (MINECO/ERDF, EU). LG acknowledges the support by FCT-Fundacao para a Ciencia e a Tecnologia, I.P., within the scope of the research unit "Institute for sustainability and innovation in structural engineering-ISISE" (UIDP/04029/2020) and of Regional Operational Programme CENTRO2020, within the scope of the project CENTRO-01-0145-FEDER000006 (SUSpENsE). IP-A and VE acknowledge the financial support of Generalitat Valenciana by grants BEST/2018/119 and BEST/2019/008.

Hybrid structures with epoxy embedded in open-cell aluminum foam were developed by combining open-cell aluminum foam specimens with unreinforced and reinforced epoxy resin using graphene oxide. These new hybrid structures were fabricated by infiltrating an open-cell aluminum foam specimen with pure epoxy or mixtures of epoxy and graphene oxide, completely filling the pores. The effects of graphene oxide on the mechanical, thermal, and acoustic performance of epoxy/graphene oxide-based nanocomposites are reported. Mechanical compression analysis was conducted through quasi-static uniaxial compression tests at two loading rates (0.1 mm/s and 1 mm/s). Results show that the thermal stability and the sound absorption coefficient of the hybrid structures were improved by the incorporation of the graphene oxide within the epoxy matrix. However, the incorporation of the graphene oxide into the epoxy matrix can create voids inside the epoxy resin, leading to a decrease of the compressive strength of the hybrid structures, thus no significant increase in the energy absorption capability was observed.

This article reports on the fabrication and characterisation of hybrid structures prepared by impregnating an open-cell aluminum foam with polydimethylsiloxane (PDMS) or PDMS reinforced with graphene oxide, GO (PDMS nanocomposite). The effect of the PDMS and the GO on the mechanical, thermal, acoustic absorption and fire retardancy properties of the resulting hybrid structures were evaluated and compared to the individual components (PDMS, PDMS nanocomposite, open-cell aluminium foams). Results demonstrate that the use of the PDMS cured at 65 degrees C, as an void filler of the open-cell aluminium foams, changes mechanical and deformation performance, from a rubbery to brittle behaviour, however attaining a higher level of strength (quasi-static: similar to 5 MPa ; dynamic: >15 MPa) in the resulting hybrid structures. This change is due to the low chain mobility of the polymer and effective adhesion with struts of the open-cell aluminium foams. Furthermore, these hybrid structures are extremely sensitive to strain-rate testing, exhibiting a maximum compressive stress increase of more than 300% and 200%, respectively. The presence of the GO within the PDMS improves significantly the non-flammability of the hybrid structures and increases the sound absorption coefficient.

• Ministerio de Economia y Competitividad y Fondos FEDER. Proyecto RA2015-70487-R, para David Montes Gonzalez, Juan Miguel Barrigon Morillas • Fundacao para a Ciencia e a Tecnologia. P proyecto POCI-01-0145-FEDER-007633, para Luis Manuel Cortecao Godinho, Paulo Jorge Amado Mendes

[EN] We propose the application of a numerical model based on the Method of Fundamental Solutions to the estimation of the target strength (TS) of single fish, a crucial parameter for evaluating fish abundance when using active acoustical techniques. We consider a realistic beam and the influence of the evolution of the scattered field with distance maintaining the target in the far field of the ultrasonic transducer. The cases of a fluid sphere and a prolate spheroid model for the swimbladder are used to verify the application of MFS against other analytical and numerical methods. Additionally, a model considering only the swimbladder and the fishbone is presented to evaluate the differences between dorsal and ventral aspect measurements, and to understand previous experimental works performed with Atlantic salmon (Salmo salar) in floating cages., I. Perez-Arjona and V. Espinosa acknowledge funding of ACUSTUNA project ref. CTM2015-70446-R (MINECO/FEDER, UE), and UPV grants of PAID-00-15 and GVA BEST/2015/270. L. Godinho acknowledges the funding by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT - Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007633. The authors would like to thank Dr. Manuel Bou and Carlos Albino for the technical assistance with work-station procedures.

This paper presents an experimental study about the acoustic and thermal behaviour of a novel type of sandwich panel solution based on Cross-Laminated Timber (CLT). The layout of the new panel, named Cross-Insulated Timber (CIT), is similar to the one of a five-layer (CLT) panel, but the inner layer is made of polyurethane (PUR) rigid foam instead of timber, aiming to rationalize the wood volume and combine it with a low-density core layer for improved thermal insulation and reduced weight. For the acoustic behaviour, the study included the assessment of (i) the airborne and impact sound insulations of the developed panel, as well as of equivalent-thickness CLT solutions, and of (ii) the suitability of analytical models to describe such sound insulation. In general, the airborne and impact sound insulation of the CIT panels were found to be lower than that of CLT panels with equivalent thickness, namely due to their mass differences. Analytical models available in the literature to describe the airborne sound insulation of typical sandwich panels failed to describe the behaviour of the CIT panels. The Sharp model for homogeneous isotropic elements was able to provide a good description of the airborne sound insulation behaviour of the thicker CIT panels; however, it also failed to describe the behaviour of the thinner CIT panels. An adaptation of such model, by replacing the typical critical frequency due to bending by the dilatational frequency, enhanced the accuracy of predictions. An empirical model to estimate the impact sound insulation of both CIT and CLT panels was also proposed and fitted quite well the results. Regarding the thermal behaviour, some variability was found in the thermal resistance of the CLT and CIT panels, which was attributed to the intrinsic scatter in their material properties, namely for wood. Despite such variability on the coefficient of thermal conductivity of wood, its overall influence on the thermal resistance of the CIT panel solutions was actually marginal due to the considerably lower thermal conductivity of PUR. As expected, the analytical model (conventional heat conduction) was able to predict the thermal resistance of the CIT panels, with good accuracy.

An important challenge for acoustic engineers in room acoustics design is related to the acoustic performance of multi-purpose auditoriums, which are typically designed to suit several performance requirements. With this intent, the analysis of several scenarios is usually performed individually, and then an acceptable solution, that may be adapted to several situations, is selected. One way of providing a more appropriate acoustic performance for each function of the auditorium is using variable sound absorption techniques to control reverberation and other relevant acoustic phenomena associated to sound perception. In this paper, the acoustic behavior of a perforated system that may be suitable for achieving a variable acoustic solution for room acoustic design is addressed. In the design of a cost-effective solution, the surface appearance is kept unchanged, while variable acoustic behavior is achieved either by closing the holes in the back face of the perforated panel or by placing a porous material in varying positions inside the backing cavity, thus accomplishing different acoustic requirements within a multipurpose auditorium. An analytical approach, based on the transfer matrix method is employed for preliminary acoustic sound absorption assessment provided by the system and to develop optimized solutions. Diffuse sound absorption is then computed and used to simulate, by the ray-tracing method, the acoustic behavior of a multipurpose auditorium to demonstrate efficient acoustic performance for different types of use. This work is financed by FEDER funds through the Competitivity Factors Operational Programme—COMPETE within the scope of the project ADJUST—Development of acoustic panels progressively adjustable with smart acting—SII & DT Project CENTRO-01-0247-FEDER-033884. This work was partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020 and by Regional Operational Programme CENTRO2020 within the scope of project CENTRO-01-0145-FEDER-000006 (SUSpENsE).

In this work, ground-borne vibrations due to pile driving impact are analyzed. A comparison between numerical results and experimental responses obtained in a low strain test measurement is presented. The experimental campaign is held at a construction site next to the Faculty of Engineering of the University of Porto (Portugal). The low strain test is carried out with 13 accelerometers equally distanced in a straight line and the ground vibrations are measured at the ground surface for several blows induced by an impact hammer. Soil properties and stratification are determined through non-intrusive geophysical tests - seismic refraction tests and SASW (Spectral Analysis of Surface Waves) tests. The numerical model is developed in time domain with the same characteristics of the construction site, considering a finite element axisymmetric formulation and an effective semi-explicit/explicit time marching procedure. The numerical results present good agreement with the in situ measured response, which indicates the effectiveness of the developed numerical model. In the sequence, a parametric study is developed and the results compared to previous numerical and experimental studies available in the literature.

This paper presents an experimental and numerical study about the flexural and compressive behaviour of a novel type of sandwich panel solution based on Cross-Laminated Timber (CLT). The layout of the new panel, named Cross-Insulated Timber (CIT), is similar to the one of a five-layer (CLT) panel, but the inner layer is made of polyurethane rigid foam instead of timber as in Structural Insulated Panels (SIP), aiming to rationalize the wood volume and combine it with a low-density core layer for improved thermal insulation and reduced weight. The study about the mechanical behaviour of CIT included the variation of the layers' thicknesses, in order to assess their influence in the mechanical behaviour and also the suitability of the numerical models to describe such behaviour. The experimental campaign included bending tests and axial compression tests in full-scale CIT beams (only one lamella at the external layers) and panels (multiple lamellas at the external layers) and SIP beams, which allowed assessing their global stiffness, resistance, buckling behaviour and failure modes. In bending, both CIT and SIP presented non-linear behaviour, due to the polymeric foam core, and their load capacity was governed by the shear failure of the core, which was the dominant failure mechanism. For the bending tests, the Timoshenko and Kreuzinger analytical models described quite well the deflection observed in the linear range, while for the non-linear branch of the load-displacement curves, the developed finite element model provided good accuracy. The Euler’s buckling load formula adapted for sandwich panels predicted quite well the buckling load measured in the compression tests. The results showed the potential of the CIT solution for structural applications and of the analytical and numerical models for design purposes.

In this paper, a highly straightforward approach is presented to simulate acoustic wave propagation in the presence of barriers. This formulation is particularly suited to tackle practical problems requiring the maximisation of noise loss by the optimal location of barriers, since the standard finite element approach has a significant computational burden from remeshing. The discontinuity-enriched elements here proposed are formulated considering very simple manipulations of standard elemental matrices to directly represent the effects of acoustic barriers. The formulation is developed within the context of the partition of unity method but avoids cumbersome enrichment procedures usually required to geometrically describe a strong discontinuity, and enables a very versatile simulation methodology. Embedded discontinuities are modelled independently of the underlying spatial discretisation. Locally-defined degrees of freedom solely related to the elements crossed by the discontinuity are used in the analysis to represent the discontinuous fields. In addition, a locally-defined time-marching formulation is employed to further enhance the solution-finding steps. Numerical applications to sound thin barriers and cracks are presented to assess the performance of the new technique.

The dynamic changes in a traditional layout of a short-span timber floor due to deterioration on supports were investigated experimentally and numerically. The floor was evaluated for its normal si...

Some of the most extended approaches to widen the sound absorption bandwidth of perforated panel absorbers are the use of different cavity depths or multi-layer arrangements. Unfortunately, these solutions are rarely adopted in practice because of the technical installation difficulties or the large space requirements. This work explores an alternative compact solution consisting of a multi-size perforated panel absorber with micro-perforated partitioned cavities. While multi-size perforated panel absorbers with rigidly partitioned cavities show a wider sound absorption effective bandwidth when compared to those using single sized holes (i. e. multiple resonances instead of single resonance), the use of micro-perforated partitions was found to further broaden it and hence improve their sound absorption performance. A simplified approximate model for the prediction of the acoustic properties of such devices was derived using the Equivalent Circuit Method (ECM) and the Maa model for MPPs (Micro-Perforated Panels). Results in terms of the sound absorption coefficient under normal incidence showed a good agreement when compared to finite element simulations both for the cases with rigid and micro-perforated partitions. In addition, a parametric study was found very helpful to understand the influence of the geometrical features of the micro-perforated partitions on the acoustic behavior of the resonator, thus being useful for its design and analysis. Dissemination of this work was supported by COST (European Cooperation in Science and Technology) through the COST Action CA15125 – DENORMS: ‘‘Designs for Noise Reducing Materials and Structures”. The work was developed within the scope of the CENTRO-01-0247-FEDER-033884 (ADJUST) Project, funded by FEDER funds through the Regional Operational Programme CENTRO2020. This work was also partly supported by FEDER funds through the Competitivity Factors Operational Programme – COMPETE and by national funds through FCT – Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007633 (ISISE).

[EN] The use of periodic structures in acoustic applications has interested the scientific community in the last two decades. Although in-depth research has been thoroughly performed, many issues have still not been solved. Computational analysis of sonic structures using realistic 3D models still poses significant problems, and most of the published results correspond to 2D problems. Analysing 3D problems of such structures using conventional methods demands large computational resources, which may be prohibitive. This paper proposes a new approach for such 3D problems making use of a highly efficient Method of Fundamental Solutions (MFS) approach to deal with sonic crystals made of 3D scatterers, infinitely repeated with constant spacing along one direction. The method makes use of a special form of the acoustic fundamental solutions which can be highly efficient in such analysis, while allowing just the cell that is repeated to be effectively modelled. Verification of the model is provided by first comparing its results with those from an ACA-MFS model. Results are compared with those from a FDTD algorithm, and a parametric study is presented revealing the 3D character of the computed responses, and evidencing the formation of acoustic band-gaps at specific frequency bands associated with the Bragg effect., The EU funding support in the scope of COST (European Cooperation in Science and Technology) through the COST ActionPlease check funding information and confirm its correctness. CA15125 - DENORMS: "Designs for Noise Reducing Materials and Structures" is here also acknowledged.

Many construction operations induce significant vibrations in soils, which propagate and interfere with nearby buildings. Besides the physical effect on existing structures, these vibrations cause discomfort to building users, and are themselves a limiting factor for the execution of some operations. It is the case of impact pile-driving operations, inducing the propagation of different wave types in the soil. The present paper presents an initial study on the applicability of FEM-based time-marching algorithms for the simulation of this propagation. The paper first presents the proposed time-marching techniques, verifying their results with analytical solutions. Besides the time-marching algorithm, the effect of the order of the finite element on the accuracy of the results is also assessed, considering linear and quadratic elements. Numerical simulation of the ground wave propagation due to an impact load is then presented and the corresponding results are analyzed.

A relatively new concept of sound absorption herein denominated as Metaporous concrete is presented, consisting of a porous concrete-based sound absorber in which different acoustic resonators are embedded. Two finite element models were implemented, using the fluid-equivalent theory to describe Metaporous concrete solutions. A Helmholtz resonator, porous concrete samples, and a Metaporous concrete prototype were built and tested through experimental techniques based on the use of an impedance tube. The fluid-equivalent complex properties were validated with comparisons between analytical predictions and experimental data. The proposed numerical tools were presented as an efficient methodology to predict the sound absorption behavior of Metaporous concrete solutions, where an excellent approach between the simulated results and experimental data is shown. The parametric study shows efficient strategies to increase the sound absorption behavior and to feature the two sound absorption coefficient peaks provided by Metaporous concrete solutions (i. e. from the acoustic resonator and the porous concrete, respectively). The denominated configuration MPCd was highlighted because of the great proximity of these two sound absorption peaks. The inclusion of non-trivial resonant structures in porous concrete, building a Metaporous concrete, can be proposed as an excellent solution to be adopted for noise control in civil engineering exterior applications. This work was financed by COST Action DENORMS CA15125, supported by COST (European Cooperation in Science and Technology). This work was developed within the scope of the POCI-01-0247-FEDER-033990 (iNBRail) Project, funded by FEDER funds through COMPETE 2020, Portugal 2020. The authors also acknowledge funds through FCT – Foundation for Science and Technology within the scope of the project R&D unit “Institute for sustainability Institute for Sustainability and Innovation in Structural Engineering (ISISE) - (UIDP/0409/2020)", and through the Regional Operational Programme CENTRO2020 within the scope of the project CENTRO-01-0145-FEDER-000006.

Sonic crystal acoustic screens have been in progressive research and development in the last two decades as a technical solution for mitigating traffic noise. Their behaviour is quite different from that observed in classical barriers, with the latter being based on physically blocking the direct sound propagation path (only allowing diffracted noise to reach sensible receivers), and sonic crystals providing attenuation efficiency based on the creation of “band-gaps” at specific frequency ranges, due to the Bragg’s interference phenomenon. The distinct physical mechanisms of these two types of noise barriers complicates the use of classical simplified or even numerical models developed for traditional barriers to simulate and predict the attenuation performance of a sonic crystal, and alternative methods become thus required. In the acoustics scientific literature, several authors have proposed estimation and simulation methods based on different numerical tools to predict the sound insulation provided by these new noise abatement solutions. This paper presents a comparative evaluation of some of these methods, with emphasis on the assessment of their accuracy versus memory usage in order to determine which one is the most suitable for optimization methodologies in the design of new devices with improved acoustic performance.

Noise pollution is a major environmental problem due to its impact on human health and implications for other spheres of society. Since road traffic is the main source of noise pollution, the use of measurement methodologies to accurately determine the environmental noise levels to which the facades of buildings in cities are exposed is an important issue. This paper presents an experimental study in urban environments that uses different configurations to evaluate the influence of the position of the microphone and the parking lanes on the levels of road traffic noise to which the population is exposed. In urban settings in which sound waves propagate without obstacles between the lanes of traffic and the receivers, broadband results for the differences between noise levels measured by microphones placed at heights of 4.0 and 1.5 m showed a significant increase with an increase in the distance between the microphone and sound source of between −0.8 and 0.9 dBA over a range from 2 to 8 m. This difference between the two microphones was greater at points where a lane of parked vehicles was located between the road traffic lanes and the receivers were placed near the facades of building. At the same heights, the broadband difference in sound levels ranged from 2.7 to 4.5 dBA. This acoustic shielding effect due to the presence of parked vehicles started to be relevant in the 250 Hz band and increased progressively with frequency. Taking into account these experimental results and the recommendations in the European Noise Directive, it would be important to apply corrections to sound indicators for road traffic noise that are related to the height of the microphone. Making a distinction between urban configurations with and without lines of parked vehicles between the microphone and the road traffic lanes would be advisable.

This paper deals with the acoustic performance of timber and timber-concrete floor solutions assessed through an experimental campaign. In the case of the composite solutions, two types of concrete were adopted: a normal and a lightweight composition, the last one incorporating expanded cork aggregates. The acoustic tests were performed under controlled conditions in laboratory, to determine the airborne and impact sound insulations. The basic solutions were also evaluated including the presence of a ceiling composed of gypsum plasterboard and mineral wool. The results reveal a promising behavior of the tested solutions, particularly the composite solutions.

Vibrations induced by underground railway traffic have been receiving special attention from the technical and scientific communities, and different models for their prediction can be found in the literature. Since the tunnel can be seen as a longitudinally invariant structure, a 2.5D approach can be applied, minimizing the computational requirements without losing the 3D character of the problem. A global numerical strategy that allows simulating the vehicle–track–tunnel–soil interaction is proposed here. Tunnel–soil interaction is accounted by coupling the Finite Element Method and the Method of Fundamental Solutions. This model is then linked with a train–track interaction model, allowing to simulate the complete process of vibration propagation from the vehicle to the soil. The model is verified against reference solutions, and its application is illustrated for a practical engineering problem. The presented results indicate that the method can be quite accurate and competitive, when compared with other currently available models.

Vibration induced by vehicles is a significant problem in large cities causing a major impact on human activities, comfort and health. Besides well-known strategies to mitigate vibrations and their effects, innovative methods are being devised using novel physical concepts. Those are already well-developed for the case of acoustic barriers, for example made of periodically arranged elements (known as “sonic” or “phononic” crystals), however the shielding of structures from the effect of vibrations is still in an earlier development stage. In this context, this paper describes several studies on the concept of a periodic buried structure, made of stiff inclusions (e.g. concrete), deployed with a geometrical arrangement that may allow efficient filtering of dominant vibration frequencies. A 3D finite element model is used formulated in time domain to perform a detailed numerical assessment of the effectiveness of the proposed shielding device. Simulations are performed using a time-marching algorithm to allow an efficient calculation procedure. Results are promising, clearly revealing the existence of band gaps of large attenuation, although limitations related to the existence of guided waves travelling along the inclusions are also identified.