This paper presents the first results of the flanksound project, a study promoted by Rotho Blaas srl regarding flanking transmission between CLT panels jointed with different connection systems. The vibration reduction index Kij is evaluated according to the EN ISO 10848 standard by measuring the velocity level difference between CLT panels. The performance of the X-RAD connection system is compared to the performance of a traditional connection system made of shear angle bracket and hold-down, both the configurations being tested with and without a resilient material placed between the construction elements. Concerning the traditional system, the influence of the difference sizes and types of fasteners - including the method of nailing or screwing - was also evaluated. The results of the measurements exposed in this work will hopefully contribute to the development of the acoustic design of timber buildings by providing a solid database of Kij values, which can be used to forecast the acoustic performance of the building according to the prediction models proposed in EN 12354-1.
Vibrations induced by people walking is one of the most important issue in timber floor design. Low natural frequency and low mass require a careful analysis in order to prevent significant annoyance and to guarantee an acceptable human comfort. This paper is concerned with the assessment of vibration performance of a timber-concrete composite timber floor and a cross laminated timber floor used in two timber buildings under construction in Trento (Italy). Different approaches suggested by Standards and literature were employed: analytical methods, numerical analyses and laboratory tests. About analytical methods the uniformed distributed load deflection criterion (ULD), the Eurocode 5 criterion and some criterions from literature were compared, whereas the Vibration Dose Value (VDV) method, as suggested by ISO 10137, was used for the numerical models and the laboratory tests. The numerical analyses were carried out by means of a finite element modelling. The load due to footfall was simulated by static and dynamic vertical forces. The laboratory tests were characterized by thirty walking tests for each floor. Impact testing with modal hammer was also undertaken in order to investigate the dynamic properties of the specimens. All results are compared and discussed.
As 6-storey wood-frame, massive-timber and hybrid wood buildings are increasingly accepted by more jurisdictions across Canada, there is a need to develop reliable elevator shaft designs that meet the minimum structural, fire, and sound requirements in building codes. Elevator shaft walls constructed with wood-based materials have the advantages of material compatibility, use of sustainable materials, and ease of construction.
In this exploratory study, selected elevator shaft wall designs built with nail-laminated-timber (NLT) structural elements were tested to investigate their sound insulation performance because little is known about the sound insulation performance of such wall assemblies. The tests were carried out in an acoustic mock-up facility in accordance to standard requirements, and provide preliminary data on the sound insulation performance of elevator shaft walls built with NLT panels.
Four different elevator shaft walls built with NLT panels were tested and their measured apparent sound insulation class (ASTC) ratings ranged from 18 to 39 depending on their construction details. Some of the reasons that may have contributed to the ASTC ratings obtained for the elevator shaft walls described in this report as well as recommendations for future designs were provided.
It is recommended to continue improving the sound insulation of elevator shaft walls built with NLT panels to meet or exceed the minimum requirements in building codes.
The wood engineering community has dedicated a significant amount of effort over the last decades to establish a reliable predictive model for the load-carrying capacity of timber connections under wood failure mechanisms. Test results from various sources (Foschi and Longworth 1975; Johnsson 2003; Quenneville and Mohammad 2000; Stahl et al. 2004; Zarnani and Quenneville 2012a) demonstrate that for multi-fastener connections, failure of wood can be the dominant mode. In existing wood strength prediction models for parallel to grain failure in timber connections using dowel-type fasteners, different methods consider the minimum, maximum or the summation of the tensile and shear capacities of the failed wood block planes. This results in disagreements between the experimental values and the predictions. It is postulated that these methods are not appropriate since the stiffness in the wood blocks adjacent to the tensile and shear planes differs and this leads to uneven load distribution amongst the resisting planes (Johnsson 2004; Zarnani and Quenneville 2012a). The present study focuses on the nailed connections. A closed-form analytical method to determine the load-carrying capacity of wood under parallel-to-grain loading in small dowel-type connections in timber products is thus proposed. The proposed stiffness-based model has already been verified in brittle and mixed failure modes of timber rivet connections (Zarnani and Quenneville 2013b).
FPInnovations launched the “Next Generation Building Systems” research program to support the expansion and diversification of wood into new markets. “Next Generation Wood Buildings” can be described as buildings that implement design and construction practices, and use innovative wood-based materials and systems beyond those defined and addressed in current building codes. As part of this program, the serviceability research focuses on addressing issues related to floor and building vibrations, sound transmission and creep.
CLT is a next generation wood building material, which is a promising alternative to concrete slabs. To facilitate wood expansion into the market traditionally dominated by steel and concrete, several CLT buildings have been designed or built. Taking this opportunity, we conducted this study on two CLT buildings in the province of Quebec (i.e.,Desbiens and Chibougamau) to collect data that will form a database for the development of design provisions and installation guides for controlling vibrations and noise in CLT floors and buildings. The study also provides some information to designers and architects to strengthen their confidence in using CLT in their building projects. It is our hope that the collaboration through this study demonstrates to both designers and users of CLT buildings that if we work together, we can build good quality CLT buildings.
During the construction, ambient vibration tests were conducted on the two CLT buildings to determine their natural frequencies (periods) and damping ratios. Vibration performance tests were conducted on selected CLT floors to determine their frequencies and static deflections. ASTM standard sound insulation tests were conducted on the selected CLT walls and floors in Chibougamau CLT building to develop the sound insulation solutions. After the two CLT buildings were completed, ASTM sound insulation tests were conducted in the selected units to determine the Field Sound Transmission Class (FSTC) of the finished floors and walls, and the Field Impact Insulation Class (FIIC) of the finished floors.
We found that in general, the vibration performance of these two CLT buildings and their floor vibration performance are functional. The efforts made by the design engineers, the architects, and the contractors to make it happen are commendable, considering the lack of design provisions and guidelines in building codes for controlling vibrations in such innovative wood floor and buildings. The sound insulation of the selected units in Chibougamau building was very satisfactory. This confirmed that with proper design, construction, and installation of the sound insulation solutions studied in this report, CLT floors, walls and buildings can achieve very good sound insulation.
Some specific recommendations for CLT building sound insulation:
If flanking paths can be minimized, then it is expected that better sound insulation than what we measured on the CLT floors during the building construction will be achieved ;
Increasing the stud spacing from 400mm to 600mm for the wood stud walls enhances the airborne sound insulation of the current wood stud-CLT wall assemblies tested in this study ;
Decoupling ceiling from the structure frame and from the CLT floors is a significant factor for cost-effective sound insulation solutions ;
Selection of solutions for FSTC and FIIC above fifty (50) for non-carpeted CLT floors will ensure the satisfaction of the majority of occupants ;
Conducting subjective evaluation is useful to ensure occupants satisfaction ;
For implementation of the sound insulation solutions for floating floors, it is necessary to consult wood flooring and ceramic tiles installation guides for floating the flooring.
Understanding the inherent damping mechanisms of floor vibrations has become a matter of increasing importance following the development of new composite floor layouts and increased span. The present study focuses on the evaluation of material damping in timber beam specimens with dimensions that are typical of common timber floor structures. Using the impact test method, 11 solid wood beams and 11 glulam beams made out of Norway Spruce (Picea abies) were subjected to flexural vibrations. The tests involved different spans and orientations. A total of 420 material damping evaluations were performed, and the results are presented as mean values for each configuration along with important statistical indicators to quantify their reliability. The consistency of the experimental method was validated with respect to repeatability and reproducibility. General trends found an increasing damping ratio for higher modes, shorter spans, and edgewise orientations. It is concluded from the results that material damping of timber beams of structural dimensions is governed by shear deformation, which can be expressed more conveniently with respect to the specific mode shape and its derivatives.
As interest has grown in using mass timber for commercial building projects, so too has the need to better understand the vibration characteristics of mass timber floor systems. Vibration requirements typically drive the spans and thicknesses of mass timber floors. Our team has a unique opportunity to close several crucial knowledge gaps while designing the new Health Sciences Education Building (HSEB) at the University of Washington, which is under design and is scheduled to start construction in the summer of 2019.
Case Study for Design Guide – The HSEB will be designed using the U.S. Mass Timber Floor Vibration Design Guide. Vibration performance will be measured to further validate or refine the model calibration suggestions put forth in the Design Guide.
Damping Measurements – The HSEB will contain a wide variety of program spaces with varying damping characteristics that will be measured and correlated.
Stiffness Measurements – Laboratory and in situ testing will be performed on a several floor framing systems. This will include a variety of span lengths and member depths. It will also include composite behavior of concrete and CLT floors with different connection types.
The results of this study will allow for more accurate predictions of floor vibrations. This will significantly reduce the cost of mass timber systems in way that is repeatable and scalable for future architects and engineers.