Serviceability performance studied covers three different performance attributes of a building. These attributes are 1) vibration of the whole building structure, 2) vibration of the floor system, typically in regards to motions in a localized area within the entire floor plate, and 3) sound insulation performance of the wall and floor assemblies. Serviceability performance of a building is important as it affects the comfort of its occupants and the functionality of sensitive equipment as well. Many physical factors influence these performances. Designers use various parameters to account for them in their designs and different criteria to manage these performances. Lack of data, knowledge and experience of sound and vibration performance of tall wood buildings is one of the issues related to design and construction of tall wood buildings.
In order to bridge the gaps in the data, knowledge, and experience of sound and vibration performance of tall wood buildings, FPInnovations conducted a three-phase performance testing on the Origine 13-storey CLT building of 40.9 m tall in Quebec city. It was the tallest wood building in Eastern Canada in 2017.
Key point to development of environmentally friendly timber structures, appropriate to urban ways of living, is the development of high-rise timber buildings. Comfort properties are nowadays one of the main limitations to tall timber buildings, and an enhanced knowledge on damping phenomena is therefore required, as well as improved prediction models for damping.
The aim of this work has consequently been to estimate various damping quantities in timber structures. In particular, models have been derived for predicting material damping in timber members, beams or panels, or in more complex timber structures, such as floors. Material damping is defined as damping due to intrinsic material properties, and used to be referred to as internal friction. In addition, structural damping, defined as damping due to connections and friction in-between members, has been estimated for timber floors.
This study focuses on the vibrational behaviour of 3, 5 and 7-layer cross-laminated timber (CLT) plates supported on two sides with different support conditions. Three end support setups are proposed; 1) top load over the two supported edges, 2) direct fastening to support using self-tapping screws, 3) steel angle bracket support. The measured response parameters are natural frequencies, damping, and static deflection under a point load. The rotational stiffness with load, screws and steel angle brackets will be characterized through static tests. In addition, the effect of the span is studied by varying the test span and repeating the vibration and deflection tests. The laboratory tests will be supplemented with analytical modelling. The expected outcome is the development of approaches to more accurately calculate the natural frequency and static deflection under a point load, which can account for the influence of common support conditions encountered in service.
Ninth European Conference on Noise Control (Euronoise)
June 10-13, 2012, Prague, Czech Republic
In residential multi-storey buildings of timber it is of great importance to reduce the flanking transmission of noise. Some building systems do this by installing a vibration-damping elastic interlayer, Sylomer or Sylodyn , in the junction between the support and the floor structure. This interlayer also improves the floor vibration performance by adding damping to the structure. In the present work the vibration performance of a floor with such interlayers has been investigated both in laboratory and field tests. A prefabricated timber floor element was tested in laboratory on rigid supports and on supports with four different types of interlayers. The results are compared with in situ tests on a copy of the same floor element. The effect on vibration performance i.e. frequencies, damping ratio and mode shapes is studied. A comparison of the in situ test and the test with elastic interlayer in laboratory shows that the damping in situ is approximately three times higher than on a single floor element in the lab. This indicates that the damping in situ is affected be the surrounding building structure. The achieved damping ratio is highly dependent on the mode shapes. Mode shapes that have high mode shape coefficients along the edges where the interlayer material is located, result in higher modal damping ratios. The impulse velocity response, that is used to evaluate the vibration performance and rate experienced annoyance in the design of wooden joist floors, seems to be reduced when adding elastic layers at the supports.
This paper describes the design of a system to monitor floor vibrations in an office building and an analysis of several months worth of collected data. Floors of modern office buildings are prone to occupant-induced vibrations. The contributing factors include long spans, slender and flexible designs, use of lightweight materials and low damping. As a result, resonant frequencies often fall in the range easily excited by normal footfall loading, creating potential serviceability problems due to undesirable levels of vibrations. This study investigates in-situ performance of a non-composite timber-concrete floor located in a recently constructed innovative multi-storey office building. The floor monitoring system consists of several displacement transducers to measure long-term deformations due to timber and concrete creep and three accelerometers to measure responses to walking forces, the latter being the focus of this paper. Floor response is typically complex and multimodal and the optimal accelerometer locations were decided with the help of the effective independence-driving point residue (EfI-DPR) technique. A novel approach to the EfI-DPR method proposed here uses a combinatorial search algorithm that increases the chances of obtaining the globally optimal solution. Several months worth of data collected by the monitoring system were analyzed using available industry guidelines, including ISO2631-1:1997(E), ISO10137:2007(E) and SCI Publication P354. This enabled the evaluation of the floor performance under real operating conditions.
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.
In order to address the lack of measured natural frequencies and damping ratios for wood and hybrid wood buildings, and lack of knowledge of vibration performance of innovative CLT floors and sound insulation performance of CLT walls and floors, FPInnovations conducted a series of performance testing at the Wood Innovation Design Centre (WIDC) in Prince George, BC in April 2014, during construction, and in May 2015, after building completion and during its occupation.
This report describes the building, tested floor and wall assemblies, test methods, and summarizes the test results. The preliminary performance data provides critical feedback on the design of the building for resisting wind-induced vibration and on the floor vibration controlled design. The data can be further used to validate the calculation methods and tools/models of dynamic analysis.
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.
In the present work the change in natural frequencies, damping and mode shapes of a prefabricated timber floor element have been investigated when it was integrated into a building structure. The timber floor element was first subjected to modal testing in laboratory with ungrounded and simply supported boundary conditions, and then in situ at different stages of building construction. The first five natural frequencies, damping ratios and mode shapes of the floor element and the entire floor were extracted and analysed. It may be concluded that the major change in natural frequencies occur as the floor element is coupled to the adjacent elements and when partitions are built in the studied room, the largest effect is on those modes of vibration that largely are constrained in their movement. The in situ conditions have a great influence on the damping, which depends on the damping characteristics of the supports, but also on the fact that the floor is integrated into the building and interacts with it. There is a slight increase of damping in the floor over the different construction stages and the damping values seem to decrease with ascending mode order.