The growing diffusion of cross-laminated timber structures (CLT) has been accompanied by extensive research on the peculiar characteristics of this construction system, mainly concerning its economic and environmental benefits, lifecycle, structural design, resistance to seismic actions, fire protection, and energy efficiency. Nevertheless, some aspects have not yet been fully analysed. These include both the knowledge of noise protection that CLT systems are able to offer in relation to the possible applications and combinations of building elements, and the definition of calculation methods necessary to support the acoustic design. This review focuses on the main acoustic features of CLT systems and investigate on the results of the most relevant research aimed to provide key information on the application of acoustic modelling in CLT buildings. The vibro-acoustic behaviour of the basic component of this system and their interaction through the joints has been addressed, as well as the possible ways to manage acoustic information for calculation accuracy improvement by calibration with data from on-site measurements during the construction phase. This study further suggests the opportunity to improve measurement standards with specific reference curves for the bare CLT building elements, in order to compare different acoustic linings and assemblies on the same base. In addition, this study allows to identify some topics in the literature that are not yet fully clarified, providing some insights on possible future developments in research and for the optimization of these products.
The growing interest in timber construction and using more wood for civil engineering applications has given highlighted importance of developing non-destructive evaluation (NDE) methods for structural health monitoring and quality control of wooden construction. This study, critically reviews the acoustic emission (AE) method and its applications in the wood and timber industry. Various other NDE methods for wood monitoring such as infrared spectroscopy, stress wave, guided wave propagation, X-ray computed tomography and thermography are also included. The concept and experimentation of AE are explained, and the impact of wood properties on AE signal velocity and energy attenuation is discussed. The state-of-the-art AE monitoring of wood and timber structures is organized into six applications: (1) wood machining monitoring; (2) wood drying; (3) wood fracture; (4) timber structural health monitoring; (5) termite infestation monitoring; and (6) quality control. For each application, the opportunities that the AE method offers for in-situ monitoring or smart assessment of wood-based materials are discussed, and the challenges and direction for future research are critically outlined. Overall, compared with structural health monitoring of other materials, less attention has been paid to data-driven methods and machine learning applied to AE monitoring of wood and timber. In addition, most studies have focused on extracting simple time-domain features, whereas there is a gap in using sophisticated signal processing and feature engineering techniques. Future research should explore the sensor fusion for monitoring full-scale timber buildings and structures and focus on applying AE to large-size structures containing defects. Moreover, the effectiveness of AE methods used for wood composites and mass timber structures should be further studied.
Acoustic emission (AE) characteristics of full-hole bolt-bearing testing on structural compositelumbers (SCL) including laminated veneer lumber (LVL) and oriented strand lumber (OSL) were investigated. The main conclusion is that AE cumulative counts vs time curves of the tested SCL in this study can be characterized with three distinct regions in terms of AE count rates: Region I with a lower constant count rate, Region II with varied and increased count rates, and Region III with a higher constant count rate. Differences in AE count rates of these three regions occurred between LVL and OSL. Also, within each tested SCL, differences in AE count rates were observed among the three regions. These differences in terms of AE count rates between two tested SCL indicate that different types of wood-based composites might have different AE characteristics in terms of the count rate changes when they are subjected to increased bolt compression load. In other words, these differences in AE characteristics between the two tested materials suggest AE “signatures” do exist for SCL bolt connections.
Delamination and decay are common structural defects in old glued laminated timber (glulam) buildings, which, if left undetected, could cause severe structural damage. This paper presents a new damage detection method for glulam inspection based on moment analysis and wavelet transform (WT) of impact acoustic signals. Acoustic signals were collected from a glulam arch section removed from service through impact testing at various locations. The presence and positions of internal defects were preliminarily determined by applying time centroid and frequency centroid of the first moment. Acoustic signals were then decomposed by wavelet packet transform (WPT) and the energy of the sub-bands was calculated as characteristics of the response signals. The sub-bands of 0–375 Hz and 375–750 Hz were identified as the most discriminative features that are associated with decay and delamination and therefore are indicative of the presence of delamination or decay defects. A defect diagnosis algorithm was tested for its ability to identify internal decay and delamination in glulam. The results show that depth of delamination in a glulam member can be determined with reasonable accuracy.
With the emergence of cross laminated timber (CLT) as a structural material on the global market, the need to understand the acoustical behavior of buildings constructed with the material grows. CLT faces a set of challenges that concrete or masonry do not; being low density, high in stiffness, sometimes isotropic and sometimes orthotropic depending on the composition. Flanking sound transmission often becomes an issue in the acoustic performance of mass timber buildings. While direct sound transmission can be treated with conventional methods e.g. additional layers, the flanking paths are more complicated to treat since they need to transfer loads over the length of the element. This master’s thesis aims to investigate the flanking paths in cross laminated timber buildings by measuring the structure-borne vibration reduction index (Kij) in realized buildings. The in-field measurements are compared to standardized estimation models and lab measurements published in past research. This thesis finds that standardized estimations underestimate the performance of the examined junctions in low frequencies. The lab measurements are closer to the in-field performance but exaggerate the influence of metal connections and mass-spring behavior of junctions with elastic interlayers. Additionally the theory and results indicates that external loads on the junction play a major role in the resulting performance. Elastic interlayers are not as effective in low levels as in the high levels of any given building, presenting a challenge as mass timber structures are increasingly being built taller.
A major problem in light-weight timber floors is their insufficient performance coping with impact noise in low frequencies. There are no prefabricated solutions available in Australia and New Zealand. To rectify this and enable the implementation of light-weight timber floors, a structural floor was designed and built in laminated veneer lumber (LVL). The floor was evaluated in a laboratory setting based on its behaviour and then modified with suspended ceilings and different floor toppings. Twenty-nine different floor compositions were tested. The bare floor could not reach the minimum requirement set by the Building Code of Australia (BCA) but with additional layers, a sufficient result of R'w+Ctr 53 dB and L’nT,w + CI 50 dB was reached. Doubling of the concrete mass added a marginal improvement. With concrete toppings and suspended ceiling it is possible to reach the goal in airborne and impact sound insulation. The best result was achieved by combining of additional mass and different construction layers.
The growing availability and code acceptance of mass timber—i.e., large solid wood panel products such as cross laminated timber (CLT) and nail-laminated timber (NLT)—for floor, wall and roof construction has given designers a low-carbon alternative to steel, concrete, and masonry for many applications. However, the use of mass timber in multi-family and commercial buildings presents unique acoustic challenges.
While laboratory measurements of the impact and airborne sound isolation of traditional building assemblies such as light wood-frame, steel and concrete are widely available, fewer resources exist that quantify the acoustic performance of mass timber assemblies. Additionally, one of the most desired aspects of mass timber construction is the ability to leave a building’s structure exposed as finish, which createsthe need for asymmetric assemblies. With careful design and detailing, mass timber buildings can meet the acoustic performance expectations of most building types.
This client report on the acoustics research component regarding sound insulation of elements and systems for mid-rise wood buildings is structured into a main part and four appendices. The main part outlines the background, main research considerations and summarizes conducted research and major outcomes briefly. It is structured like the Acoustics tasks in the Statement of Work of the Mid-rise Wood research project to identify accomplishments. For details on the research, testing and results, the main part references to four appendices that contain more details including test plans, test methods, specimen descriptions and all test data that is vetted so far.
This report summarizes the acoustics research component regarding sound insulation of elements and systems for the research project on mid-rise and larger wood buildings. The summary outlines the background, main research considerations, research conducted and major outcomes. Further details of the design and the results can found in the appendix of Client Report A1-100035-02.1.
The goal of the acoustics research components was to develop design solutions for mid-rise wood and wood-hybrid buildings that comply both with the current National Building Code of Canada (NBCC) 2010 [2] requirements for direct sound insulation and with the anticipated requirements for flanking sound transmission in the proposed, 2015 version of the NBCC. In addition, the design solutions were to provide better impact sound insulation while still achieving code compliance for all other disciplines (interdependencies) as identified in the final report of the scoping study conducted in FY 2010/2011.
Architectural Testing, Inc., an Intertek company (Intertek-ATI), was contracted to conduct airborne sound transmission loss and impact sound transmission tests. The complete test data is included as attachments to this report. The full test specimen was assembled on the day of testing by Intertek-ATI. All materials provided by the client were installed on an existing Intertek-ATI assembly (Cross Laminated Timber - 175 mm) utilizing Intertek-ATI-supplied.
