Cross-laminated Timber Floor Research Articles

Annoyance evaluation of impact sounds on lightweight, concrete and cross-laminated timber floors - A comparative study

For people living in multi-unit residential buildings, neighbor noise and especially impact noise from neighbors, such as dropping objects or footsteps, can affect the quality of living of those who hear the noise. In order to support the inclusion of limits for impact noise in a future edition of the National Building Code of Canada, a project at the National Research Council of Canada has focused on the perceived annoyance from different types of impact sounds for various timber floor-ceiling assemblies. The results from listening experiments showed poor correlation between subjective ratings and objective single number metrics for impact noise due to persons walking without shoes. To extend this evaluation to a wider variety of floor-ceiling assembly types and to validate previous results, another listening experiment was conducted at the National Research Council. Annoyance ratings for ball drops, hammer impacts and footsteps on different lightweight, concrete and cross-laminated timber floor-ceiling assemblies were compared.

Impact noise calculations of CLT constructions using finite element

Cross-laminated timber (CLT) consists of multiple glued layers of wood, which have perpendicular orientation with respect to adjacent layers, and it has become an important building material due to its light weight, strength, and sustainability. One problem with CLT constructions is the impact noise, which for a bare CLT floor is poor. There thus is a need for calculation tools that can predict impact noise level of such floor constructions. For composed constructions, finite element is a flexible and usable tool. However, to simulate real measurement scenarios, the force produced by the ISO tapping machine then needs to be estimated. This paper revisits this estimation and performs calculations of the impact noise level of a CLT floor, and compares this with measured results.

A dynamic stiffness method to estimate the sound insulation of an arbitrarily installed thick cross laminated timber (CLT) plate

There is no generally accepted standard methodology to determine the dynamic constants of whole cross laminated timber (CLT) plates. Combined with the observation that CLT walls or floors are installed in situ under very different conditions to laboratory measurement conditions a methodology is sought to determine the sound insulation of CLT plates installed under arbitrary conditions without accurate information concerning the dynamic constants (and boundary conditions). The methodology may have applications where a panel can be tested in situ e.g. in pre-completion testing. In the laboratory measurement a CLT plate was mounted on the laboratory floor on two wooden joists placed at arbitrary positions to support the weight of the plate to represent a possible installation in situ.

Floor impact sound insulation performance of Korean domestic cross-laminated timber floors and the influence of resilient materials' dynamic stiffness

In this study, the floor impact sound insulation performance of floors made of korean domestic cross-laminated timber panels and with a resilient layer under concrete topping was evaluated. The properties of resilient materials used in the floors were measured to evaluate their influence on floor impact sound insulation performance. The results indicate that the highest reduction levels were provided by glass fiber, expanded polystyrene and wood fiber, in diminishing order, for both heavy-weight and light-weight floor impact sounds. Through the evaluation of dynamic stiffness and single-number quantities, a high correlation was observed at 125 Hz and 500 Hz for heavy-weight floor impact sounds and across all octave bands for light-weight floor impact sounds. The analysis of dynamic stiffness and single number quantity revealed a high correlation in both heavy weight and light weight floor impact sound. Lower dynamic stiffness was confirmed to be advantageous for reducing floor impact noise.

Characterization of inter-panel connections in CLT floors using finite element model updating

Large cross-laminated timber (CLT) floors are inevitably composed of multiple CLT panels assembled on the construction site. Due to the sheer lack of adequate numerical characterization of the inter-panel connections, CLT floors are normally modelled as monolithic structures or independent “piano keyboards”, yielding errors between simulated and the actual vibration response. This paper presents a benchmark study for a deterministic finite element (FE) model updating of so called “an equivalent elastic strip” representation of the inter-panel connections. Fitting modelling parameters of the strip, i.e. its width and material properties, featured FE modelling and modal testing of two full-scale CLT floors composed of one and two panels connected with a half-lapped joint. The floors were made of (almost) identical panels and placed on elastic mats along their shorter edges. First, the single-panel floor was used to fit material properties of the timber and the boundary conditions. Then, the FE model updating (FEMU) of two-panel floor yielded the actual values of the strip modelling parameters. Finally, these were successfully verified by direct comparison between numerically calculated and experimentally measured modal properties of a full-scale model of a simply supported three-panel floor. The results implied that the rotational stiffness of the inter-panel connection depends strongly on its vertical vibration displacement. Consequently, values of the rotational stiffness derived from rare static tests published so far cannot be used reliably in a much subtler vibration response analysis. Future studies should feature other types of the inter-panel connections in various floor layouts and a probabilistic FEMU.

Enhancing CLT floor vibration mitigation with pre-strained shape memory alloy-tuned mass dampers

Cross-laminated timber (CLT), recognised for its environmental benefits, faces challenges in its excessive human-induced vibration due to its lightweight nature. This research investigates the application of a tuned mass damper (TMD) for vibration control in CLT floor slabs, focusing on enhancing the structural performance of using this sustainable building material. The study introduces a solution by integrating Shape memory alloy (SMA) into TMD systems (SMA-TMD), utilising the properties of SMAs for effective self-centring and consistent damping, and it aims to incorporate pre-strained SMAs into TMDs to improve the damping performance of the system. Experimental testing and finite element simulations confirm that pre-straining SMA bars not only contribute to the self-centring but also considerably increase the equivalent viscous damping ratio of the SMA-TMD. Findings from the simulations demonstrate that the optimised SMA-TMD system can substantially reduce CLT floor vibration and accelerates the energy dissipation effect under human footfall loadings, overcoming one of the primary limitations of CLT in construction applications. This advancement supports the broader adoption of CLT as a sustainable building material by providing a viable solution for vibration control.

Long-term loading effect on vibration performance of CLT floors: An 896-day monitoring study

Timber, a viscoelastic material, undergoes deformation over time when exposed to sustained loads, a process known as creep. Its rising popularity as a construction material, especially for timber floors, is notable. However, the influence of creep on the dynamic characteristics of timber floors, such as their natural frequency and vibration response, is not well studied. This research focused on how long-term loading (creep) affects the vibration behaviours of a cross-laminated timber (CLT) floor. A full-scale CLT floor was constructed in a lab and subjected to long-term loading using sandbags. Over 896 days, the centroid point deflection and environmental conditions (temperature and relative humidity) were monitored. Human-induced vibration tests were carried out at the beginning, throughout, and at the end of this period. The vibration response, measured in terms of the Vibration Dose Value (VDV), was assessed at various stages of long-term loading. The findings showed a moderate positive correlation between the creep deflection and environmental conditions. The fundamental frequency slightly increased over time due to creep, and a general decrease in VDV was observed as the creep advanced.

Effect of partition walls on the vibration serviceability of cross-laminated timber floors

The current standards need more specific serviceability criteria for Cross-Laminated Timber (CLT) floors. This paper presents a comprehensive analysis of a relevant case study in Norway, which presented unexpectedly high accelerations in the CLT floors after construction. The lack of a sufficiently detailed design process resulted in the poor vibration performance of the floors, which partially compromised their functionality. The paper thoroughly investigates and discusses the experimental dynamic characterization of seven CLT floors within the considered building. The authors estimated the modal parameters and serviceability metrics based on both Eurocode 5 (EC5) and the new draft version of it. Specifically, the authors compared the analytical predictions of the fundamental frequency and the root mean square acceleration against the corresponding experimental estimations. Using a sensor-roving approach, a dense sensor configuration was adopted to describe seven floors’ mode shapes and serviceability metrics. These metrics include mean square acceleration and Vibration Dose Value. The scenarios examined in this study shed light on the significance of partition walls, a factor not considered in the practical design for serviceability verifications. The presence of partition walls can enhance the vibration comfort of timber floors by providing a stiffening effect, leading to a significant increase in the first fundamental frequency. A parametric finite element model was developed using OpenSeesPy to investigate this phenomenon further. The model, firstly validated against selected experimental results, is employed to assess the influence of partition walls on floor dynamics. The model predicts the increase in the first frequency caused by randomly generated partition walls. The paper proposes an empirical expression calibrated on the simulated data to estimate the relative increment of the floor’s fundamental frequency based on the partition walls’ layout. This formulation can be included in the analytical expression enclosed in the EC5 draft to predict the fundamental frequency of timber floors.

Experimental assessment of modal properties of hybrid CFRP-timber panels

Hybrid timber composites are becoming increasingly widespread to efficiently enhance timber performance. While carbon fibre reinforcement has been explored for strength in timber structures, its impact on vibration performance remains understudied and is crucial as mass timber buildings extend their spans and heights. This work explores the effect of carbon fibre reinforcement on the vibration performance parameters of CLT floor systems. Natural frequency, mode shape, damping and stiffness parameters are evaluated from experimental testing using the Natural Excitation Technique (NExT) combined with the Eigensystem Realization Algorithm (ERA) and robust techniques for selection of physical dynamic properties, verified against numerical finite element models. The findings reveal that, in the case of three-ply Cross-laminated Timber (CLT) panels with depths ranging from 115 mm to 135 mm, introducing reinforcement at ratios below 0.67% led to an enhancement in frequencies, registering an increase of 6% to 11%, although not explicitly accounting for changes in environmental conditions. Moreover, these reinforced panels showed a relevant increase in effective flexural stiffness, ranging from 15% to 22%, when compared to their unreinforced counterparts. This means an improved maximum span of around 4%–6% within current design limits for timber floors influenced by vibration performance. These findings enhance the understanding and design of high-performance composite timber floors, promoting the use of renewable building materials in construction.

Reliability framework for CLT floors in out-of-plane bending using Monte Carlo simulation

Sustainably sourced engineered wood products (EWP) such as cross-laminated timber (CLT) floor panels are viable alternatives to conventional concrete and steel, however their inherent natural variability increases perceived risks and limits wide-spread adoption. The reliability index (β) is the metric used by design standards to communicate allowable structural risk. Although not included directly in any structural capacity equations, it governs all the partial resistance factors and load amplification factors that inform those design code calculations. CLT floors have significant partial resistance factors due to the natural variability of the material that effectively penalise the calculated design strength of those products. By exploring their reliability there is the potential to allow these products to be designed more efficiently, leading to increased competitiveness among traditional materials and less waste. A novel statistical capacity prediction model that goes beyond a simple averaged-value strength assumption to include consideration of the variability between individual boards within a panel was validated against experimental data. A CLT database of 237 out-of-plane bending test results was collected for the first time to inform an appropriate model error factor. Monte Carlo simulation (MCS) approaches were adopted to predict the reliability levels of CLT panels by defining the material, geometrical and loading parameters as random variables and assigning each a mean, coefficient of variation and appropriate distribution. The target and calculated reliability levels were compared across both Eurocode 5 and the North American codes ANSI/APA PRG 320 and CSA O86 as the preeminent CLT design codes internationally. This study found that the calculated reliability levels met or exceeded both codes in most scenarios. The impacts of width, load ratio, material strength distribution, and CLT layups on the expected failure probabilities were explored with sensitivity analyses. The MCS framework was also applied to the calibration of an appropriate resistance factor for CLT design to inform the potential creation of an Australian CLT design code. A resistance factor of 0.85 was calibrated which falls between the equivalent European and North American code resistance factors.

Neighbourhood North: maximum gain, minimum pain – transformational office redevelopment

This article explores the project aims, challenges, solutions and lessons learned in redeveloping an existing 1980s quayside office block in southwest England. A full-height side extension introduced a double-height atrium entrance and unlocked the full potential of the office floorplates. New, larger windows were added in the existing facades, which improved the building's environmental performance, including more daylight and reduced heat loss. The client has a strong sustainability ethic and cross-laminated timber floor slabs were included in the design, which aspires to achieve BREEAM Outstanding accreditation. The project achieved an overall SCORS rating of A+, bordering on A++, at 53kg/CO2e/m2, despite the extension itself having a SCORS rating of F.

Experimental analysis of cross-laminated timber floors

Experimental analysis of cross-laminated timber floors

Cross laminated timber geometry and joinery implications on low-frequency sound transmission: FEA and Laser Doppler Vibrometry studies

Cross Laminated Timber (CLT) slabs are becoming more widespread in North American construction in large part because of the environmental advantage of lower embodied carbon when compared to concrete and steel slabs. This advantage is significantly reduced by the use of high embodied carbon layers in the mass timber floor assemblies, such as concrete or gypsum screeds, that are used to reduce the direct sound transmission. This paper presents a study on the potential to reduce low-frequency sound transmission in cross-laminated timber floors by means of geometric stiffness. A laser doppler vibrometry (LDV) experiment on two different geometries is presented. One sample has a flat geometry, the other has a folded plate design. The folded plate sample is built with the same CLT panels used on the flat one, but is made out of 12 custom parts assembled into a domical shape. Both samples were installed on a 6 × 7 foot glulam frame, subjected to shaker excitations in the low frequencies on their top side, and the vibration on their bottom sides measured with the LDV. The resulting data is used to calibrate an FEA model, and subsequently study the sound transmission implications of the sample’s boundary conditions and joinery.

On the vibroacoustics of cross-laminated timber embedded with acoustic black holes

The adoption of cross-laminated timber (CLT) in building construction is challenged by low-frequency impact noise. Conventional treatments typically involve increasing the mass of the floor assembly or employing structural decoupling techniques, both of which result in increased floor thickness. This study explores an alternative solution by examining the feasibility of embedding acoustic black holes (ABHs) into CLT floors. The ABH acts as a passive waveguide, concentrating vibrational energy in specific regions where it is transferred to damping layers and reduced. Using the finite element method, we investigated the vibroacoustic behavior of CLT plates within the 50–600 Hz frequency range. Our primary focus was on the influence of the ABH’s outer radius and the number of ABH inclusions within a CLT plate. The findings indicate that increasing the outer diameter of the ABH lowers the cut-on frequency and enhances the effective damping of the CLT plate. The increase in damping extends the effectiveness of the ABH to a broader frequency range, with the most noticeable effect above the cut-on frequency. The number of ABH inclusions impacts the structural modes below the cut-on frequency, and the optimal number of inclusions depends on the frequency of interest.

Evaluation of vibration properties of an 18-story mass timber–concrete hybrid building by on-site vibration tests

Timber–concrete hybrid structural systems are a practical option to provide tall mass timber buildings with a lateral load-resisting system. This paper discusses the dynamic behavior of an 18-story timber–concrete hybrid building based on the vibration properties evaluated by on-site vibration tests. First, microtremor measurements and human-powered excitation tests were carried out and the obtained vibration data were analyzed using a stochastic subspace identification method to derive natural frequencies, damping ratios, and mode shapes. Then, a finite-element (FE) model was developed based on detailed structural design information, and its eigenvalues and eigenvectors were compared with the test results. The vibration test results showed various mode shapes, including in-plane deformation of the floor diaphragm composed of cross-laminated timber (CLT) panels. The damping ratios in all the modes were scattered between 1 and 3%, and no frequency dependency was observed. The modal properties of the FE model agreed well with the test results by considering the additional stiffness of non-structural components. In order to simulate the in-plane deformation of the CLT floor diaphragm, detailed modeling of the connection between each CLT floor panel and the connection between CLT floor panels and concrete cores is recommended. The findings provide practitioners with an insight into dynamic properties and FE modeling methods of tall timber–concrete hybrid buildings.

Quantifying the effect of end support restraints on vibration serviceability of mass timber floor systems: Testing

Design of mass timber floor systems is commonly governed by vibration serviceability due to high stiffness-to-weight ratio and low inherent damping of timber. Research and design practice have shown that static deflection under a concentrated load and fundamental natural frequency can be effective and robust indicators for vibration performance of mass timber floors. These design parameters are normally calculated by assuming simply supported conditions in existing design methods. However, such an assumption deviates from actual floor supports, especially in platform-framed buildings, and in-situ end support restraints have been widely recognized as a significant factor affecting the vibration performance. The purpose of the study is to quantify the influence of end support restraints on vibration serviceability of mass timber floors in platform construction through a comprehensive experimental program and analytical treatment. This paper is the first part and focus specifically on the experimental work on cross-laminated timber (CLT) panels. In particular, extensive laboratory tests have been conducted on different CLT floor panels with various end support restraints induced by top loads, self-tapping screws and steel angle brackets. The fundamental natural frequency and mid-span deflection under a concentrated load were measured for each end support configuration. The rotational restraint stiffness was determined by comparing results of restrained supports to those of simple supports and represented as end fixity factors. The analysis of test results shows that the CLT floor-to-wall connection exhibited inherent non-linear behaviour and such characteristic was more significant for higher top loads. Compared with screws and brackets, the top loads dominated the partially restrained effect but such dominance gradually diminished for lower-level top loads. In addition, support wall thickness notably impacts the support restraint. It was then suggested that the clear span could be used to determine deflection and frequency in the design, but further investigation is needed.

Influence of Cross-Laminated Timber Floors and Their Connections on the Robustness of Mass-Timber Building: A Case Study on a Midrise Building

Influence of Cross-Laminated Timber Floors and Their Connections on the Robustness of Mass-Timber Building: A Case Study on a Midrise Building

Vibration reduction indices for junctions between cross-laminated timber floors and lightweight timber framed walls

Cross laminated timber elements are often used as the floors and the external walls in mass timber buildings in Canada, but the internal walls of these buildings are typically lightweight timber framed walls. The calculation of the flanking transmission loss and the apparent sound transmission class for the mix of lightweight and mass timber constructions requires the laboratory measured vibration reduction indices or flanking level differences of the different flanking paths. Junctions constructed in the new four room flanking facility at the National Research Council Canada have been used to evaluate both the vibration reduction indices and the flanking level differences of a cross laminated timber floor connected to lightweight timber walls.

Study on Heavy Weight Impact Sound Insulation of CLT Floor Slab and Reduction Performance with Floor Structure

Strategies and challenge for carbon neutrality by 2050 had become important issues all over the world. In South Korea, as a move toward carbon neutrality, interest in wooden buildings is growing continuously. In order to spread the wooden buildings, especially wooden multi-residential buildings, high floor impact sound insulation performance is required. In this study, we investigated the floor impact sound insulation performance of floor slabs with cross laminated timber (CLT) panels produced in South Korea. Moreover, laboratory measurements were conducted to grasp the reduction effect by floor covering. As a result, the heavy-weight impact sound insulation performance of CLT bare slab of its thickness of 150 mm is almost 17 dB lower than that of RC slab according to ISO717-2. Concrete topping and damping material are found to be effective to both heavy and light weight floor impact sound insulation.

Assessing acoustic performance of cross-laminated timber floors with floor covering and air-gap

Assessing acoustic performance of cross-laminated timber floors with floor covering and air-gap