Cross-laminated Timber Buildings Research Articles

Vibration-based monitoring of a cross-laminated timber building in a high seismicity zone

Vibration-based monitoring of a cross-laminated timber building in a high seismicity zone

Review and Measure Winter Thermal Performance in CLT Building: A Case Study on Meldia Research Institute for Advanced Wood

Abstract CLT (Cross Laminated Timber) as a building material could help lower the carbon footprint of construction projects. Thermal performance and comfort in CLT buildings as a place to work are very important for optimizing comfort and work quality using CLT buildings. In winter conditions, measure and review is very necessary to optimize the desired building according to the standard level of comfort when working. The aims of this research is to measure and review indoor thermal comfort of CLT building during winter, with the case study Meldia Research Institute for Advanced Wood, Fukuoka, Kitakyushu. This research method involves measuring indoor temperature intensity in winter to understand how CLT buildings can achieve an optimal balance of thermal comfort. The results of measurements using PMV analysis of both rooms with the HVAC on at a temperature of 22 degrees Celsius are that the PMV value tends from a Slightly warm condition (+1) to a Neutral (0) at each measurement time and at all points. Room 1 has the highest PMV value between slightly cool (-0.5) to Slightly warm (+1), while room 2 has the lowest value between Cool (-2) to Slightly warm (+1). These findings can guide building designers in developing architectural solutions that are sustainable and focus on occupant well-being.

Seismic assessment of SSSI effects between adjacent Cross-Laminated Timber (CLT) buildings

Urban building designs have been performed considering the behaviour of individual structures in isolation, neglecting potential seismic interactions with neighbouring buildings. In densely populated metropolitan areas, the Structure–Soil–Structure Interaction (SSSI) becomes a significant factor, capable of either amplifying or reducing the seismic response of buildings. This suggests that there is an unquantified seismic risk in densely packed urban areas, which will need to be estimated to obtain designs for more resilient infrastructure. Despite the increasing popularity of CLT as a structurally competitive material, limited attention has been given to investigating dynamic interactions between timber structures. The reduced weight of CLT structures compared to traditional materials necessitates a focused examination of the effects imposed by nearby buildings under varying soil conditions, challenging the fixed-base assumptions commonly applied in seismic analyses. This study investigates the impact of SSSI between pairs of cross-laminated timber (CLT) buildings. Three distinct building heights are considered, exploring differences in storey ratios, under five different ground motions to evaluate seismic performance comprehensively. Sixty detailed high-order three-dimensional models, treating soil and buildings as unified systems, are developed as numerical dynamic simulations. Results reveal that SSSI can significantly influence the displacement and acceleration demands of buildings, with a more pronounced effect observed in loose soil conditions. Particularly, the presence of adjacent higher buildings leads to an increase in the seismic response of the smaller structure, showing amplification effects in peak values but maintaining similar dynamic behaviour. There has been observed a clear trend of increase in the roof displacements of the smaller structure when the storey ratio of neighbouring structures increases; however, the trend of behaviour is not clear in the maximum accelerations. The study underscores the importance of understanding how nearby buildings, particularly those with more storeys, can impact the seismic response on CLT structures.

Production-oriented approach for optimal mass-customisation of floor panel layouts in cross-laminated timber (CLT) buildings

PurposeThis study aims to develop a production-oriented approach for optimal mass-customisation of floor panel layouts in cross-laminated timber (CLT) buildings. The study enables meeting building clients’ unique floor plan requirements at an optimal cost and simultaneously enhances manufacturers’ profit by minimising material and manufacturing process waste.Design/methodology/approachThe present research uses a hybrid approach consisting of field data collection, mathematical modelling, development of a Genetic Algorithm (GA) and scenario analysis. Field data includes engineered timber production information, design data and building code requirements. The study adopts the Flexible Demand Assignment (FDA) technique to formulate a mathematical model for optimising the design of mass timber buildings and employs GA to identify optimal production solutions. Scenario analysis is performed to validate model outputs.FindingsThe proposed model successfully determines the load-bearing wall placement and building spans and specifications of floor panels that result in optimal production efficiency and the desired architectural layout. The results indicate that buildings made of a single category of thickness of panels but customised in various lengths to suit building layout are the most profitable scenario for CLT manufacturers and are a cost-effective option for clients.Originality/valueThe originality of the present study lies in its mathematical and model-driven approach towards implementing mass customisation in multi-storey buildings. The proposed model has been developed and validated based on a comprehensive set of real-world data and constraints.

A new hold-down device for seismic applications in CLT buildings: Design, testing, analytical and numerical assessment

An hold-down device was designed and tested experimentally for seismic applications (Seismic Hold-Down, SHD). The magnitude of axial strength as well as the up-lift displacement capacity is mainly oriented to cross-laminated-timber (CLT) buildings with medium-to-high ductility. There is consensus in the design practice of hold-down devices for promoting, as dissipative mechanism, flexural yielding of the dowel-type connectors (e.g. nails, screws) combined to timber’s embedment. Few are the applications aiming at hold-down’s optimization as it emerges from up-to-date literature review. In this framework, SHD was conceived such that tension break-out of steel was promoted at a reduced segment (fuse) of the vertical flange. In the context of capacity design, a convenient overstrength was assumed for other failure mechanisms, e.g. anchor’s pullout, laterally-loaded steel-to-timber connection, shear-plug of timber. The mechanical response under axial load was consistently predicted by an application of the component method, i.e. global stiffness and strength were analytically-derived using simplified series of non-linear mechanical springs. Three-dimensional finite elements model was employed to investigate buckling of the fuse which might occur, during cycles, when up-lift displacement is recovering. In practical circumstances, it is recommend to design SHD devices of a CLT wall similarly to diagonal elements of steel bracings, i.e. neglecting the contribution of the compressed element. Finally, SHD is compared to traditionally-designed hold-down, which mostly dissipates (and fails) at steel-to-timber connection. Overall hysteretic response is somehow similar, although the inelastic mechanisms involved are different. For example, both the devices show pinching during cycles which for SHD is mainly caused by buckling of the fuse while, for traditional hold-down, is dominated by timber’s embedment.

Innovation ecosystems beyond construction projects – a case study of Swedish cross laminated timber building networks

ABSTRACT While innovation ecosystems have been proven effective for driving innovation in high-tech industries, their application in construction with cross laminated timber (CLT) products have received limited attention, with most studies adopting a broad perspective on ecosystems, encompassing the entire supply network around individual building projects. This study explores niche innovation ecosystems within the context of construction with CLT products. Data from 15 CLT-based building projects in mid Sweden were collected through observations and interviews and analysed using a method combining existing theory on innovation ecosystem structure with social network analysis. Innovation ecosystem structure was identified within five of the projects, encompassing two unique ecosystems. These ecosystems feature interorganisational links and actor-level expected value capture in two dimensions: value creation within the standard contractual framework of the projects and the innovation ecosystem superimposed on these projects. The novel method bridges the gap between innovation ecosystem research and CLT practices. The findings reveal that niche innovation ecosystems interact with CLT-based building projects through collaborative efforts across multiple projects and partners. These ecosystems feature alignment links that indicate both intra – and inter-project interdependencies, potentially driving innovation in construction. Role extensions within these ecosystems highlight the complexity and adaptability required in the construction industry.

Full-Scale Fire Experiments on Cross-Laminated Timber Residential Enclosures Featuring Different Lining Protection Configurations

AbstractThe adoption of timber, specifically cross-laminated timber (CLT), as a primary construction material is gaining traction due to its carbon sequestration capabilities, environmental advantages, and potential for precision manufacturing. However, the combustibility of wood raises legitimate concerns about fire safety in timber-based residential buildings. This paper investigates the fire performance of timber in a residential context, attempting to fill knowledge gaps and outline strategies for improving fire robustness in timber-built dwellings. Through comprehensive experimental studies on residential-type enclosures constructed with CLT panels, this research explores different configurations and the effects of varying degrees of non-combustible protective lining. The findings underscore the significance of considering timber surface exposure and adopting effective encapsulation strategies in CLT buildings. It has been estimated that the exposure of timber walls leads to a proportional increase in heat release rate, corresponding to the area of exposed timber surfaces and their charring rates. Consequently, the external flame has a larger projection, resulting in a much greater heat flux to the façade. Furthermore, threshold conditions for initial flaming self-extinguishment of timber defined in literature of 44.5 ± 1.2 kW/m2 have been found to be applicable to the experiments conducted in this research. Finally, it has been observed that partial encapsulation, where the protective lining will likely fall off during a fire, may hinder rather than increase the likelihood of self-extinguishment. This work contributes towards a nuanced understanding of fire dynamics in timber structures, offering insights for safer and more effective design strategies for CLT-based construction.

Modelling of Multi-Storey Cross-Laminated Timber Buildings for Vibration Serviceability

In this study, the vibration serviceability of multi-storey timber buildings is addressed. The core of this study pertains to the preparation of a comprehensive finite element model to predict modal properties for an accurate vibration serviceability checking. To that end, findings obtained from studying three multi-storey timber buildings are summarized and discussed. Two of the buildings (of seven and eight storeys) consist entirely of cross-laminated timber (CLT), while the third is a five-storey hybrid CLT-concrete building. Thanks to the detailed finite element models and modal testing results, one has the capability to conduct sensitivity analyses, classical and Bayesian model updating, and uncertainty quantifications. With these methodologies, influential modelling parameters as well as the sources of modelling error were identified. This allowed for conclusions to be drawn about the in-plane shear stiffness of the constructed walls (whose higher value causes the natural frequencies to increase by up to 25%), the soil deformability (which may cause the natural frequencies to drop by up to 20%), and the perpendicular-to-the-grain deformation of floor slabs (which may lead to an overestimation of a fundamental frequency by up to 8%).

Carbon intensity of mass timber materials: impacts of sourcing and transportation

Mass timber construction is widely considered a promising alternative construction method to reduce buildings’ total life-cycle carbon emissions because wood is a carbon sink. Cross-laminated timber (CLT) panels, manufactured by gluing lumber layers with grains at right angles, are potential low-carbon alternatives to carbon-intensive concrete and steel construction. However, most environmental impact assessment studies do not consider variation in transportation impacts within the CLT supply chain when calculating life-cycle impacts. This study investigates the embodied primary energy and the global warming potential (GWP) of CLT supply chain decisions regarding the type of timber species used, the U.S. region it is sourced from, and the location of the CLT mill. Longer transport distances in the supply chain for timber and CLT panels can contribute as much as 923 MJ/m2 (20%) of the embodied primary energy of a CLT building, and the use of a higher-density timber species increases this contribution to 1246 MJ/m2 (24%), with most of that energy derived from fossil energy sources. For perspective, the GWP of a building whose CLT panels and timber have been transported by truck over 6,000 km (252–270 kgCO2/m2) is greater than the GWP of an equivalent reinforced concrete (RC) building (245 kgCO2/m2). Thus, factors like the location of CLT processing facilities and the type of timber species can significantly impact the overall life-cycle assessment and, if chosen appropriately, can mitigate the environmental impacts of CLT construction.

Experimental investigation of dissipative connections in cross-laminated timber shearwalls

This paper presents a study investigating the performance of connections used in cross-laminated timber (CLT) shearwalls and examines the role such connections play within the capacity-based design (CD) approaches for CLT buildings. Experimental tests on hold-downs and angle brackets with two different nailing patterns, as well as different fasteners such as common nails and screws used in vertical joints are undertaken. The connection behaviour, strengths, stiffness, and ductility are presented and discussed. The experimental test results are used to evaluate the validity of CD procedures and numerical models for multi-panel CLT shearwalls. The proposed CD procedures consider the yielding hierarchy of connections and suggest overstrength factors in order to enhance the overall seismic behavior while protecting the non-dissipative elements. The research contributes to a better understanding of connection behavior, CD approaches, and the determination of appropriate overstrength factors for CLT shearwall design. By combining experimental data and shearwall-level numerical modeling, this study aids in improving the reliability of CLT shearwall design.

Development of a dry-type double floor with high vibration isolation for improvement of floor impact sound insulation performance on CLT buildings

To improve the floor impact sound insulation performance of cross laminated timber (CLT) buildings, a box-type test chamber made of CLT was constructed, and the countermeasure using a dry-type double floor was investigated. Several specimens with different area density and bending stiffness of double flooring structure were prepared, and the materials of flooring and elastic floor posts were adjusted so that the natural frequency of each specimen was about 14 Hz when the specimen was considered as a single-degree-of-freedom system. The dry-type double flooring structure affected the response at the natural frequencies not only of the slab but of walls. When installing the dry-type double flooring structure, the influence of acoustic radiation from the ceiling surface was relatively high at lower frequencies, while at higher frequencies, the influence from the walls was relatively high. The installation of the dry-type double flooring structure resulted in an improvement in floor impact sound insulation performance.

A literature review of floor impact noise characteristics in wooden apartment buildings using cross-laminated timber slab

In this study, the floor impact noise characteristics of wooden apartment buildings made of cross-laminated timber (CLT) slabs were analyzed through a literature review. Data on heavy-weight impact noise performance was gathered, including information on floor components such as floor topping materials and ceiling finishes. The collected data was primarily analyzed in terms of CLT slab thickness. The results showed that 150 mm-thick bare CLT slabs had a single number rating of 70 to 77 dB when tested with a rubber ball, but this decreased to 64 dB for a 210 mm-thick bare slab. The addition of lower ceiling finishes and floor-topping materials could reduce the heavy-weight impact noise level to around 50 dB. However, results using a bang machine indicated 5 dB higher levels than those obtained with the rubber ball. The floor impact noise characteristics of CLT structures were also compared to those of concrete structures. The paper concludes by discussing directions for improving the floor impact noise isolation performance of CLT buildings.

Effects of Building Height on the Sound Transmission in Cross-Laminated Timber Buildings—Vibration Reduction Index

High-rise wooden buildings are increasing in popularity, and they typically include cross-laminated timber in the structure. Taller buildings result in higher loads on the junctions lower down in the building, which are suggested in the literature to negatively affect the sound insulation. This study involved measurement of the vibration reduction index in four different CLT buildings, varying in height and junction details. A total of 12 junctions were measured at both high and low levels in the buildings. Among these, 10 junctions had resilient interlayers with different stiffnesses dependent on the designed quasi-permanent load, while 2 junctions lacked resilient interlayers. The results indicated that the vibration reduction index decreases lower down in the building mainly for the Wall–Wall path. The findings were consistent for all measured junctions above 400 Hz for the Wall–Wall path and for the majority of the measurements of the remaining frequency range, 400 Hz and below. The observed difference in the vibration reduction index could significantly impact the final result if a high-rise building has several flanking paths that affect the sound insulation between two apartments, and this needs to be considered during the design phase. Similar effects were shown for buildings both with and without resilient interlayers in the junctions.

CROSS Safety Report: The risk of collapse of multistorey CLT buildings during a fire

This month we present a report concerning multistorey cross-laminated timber buildings and their risk of collapse during a fire.

Predicting structure-borne noise in cross-laminated timber buildings during conceptual design

Predicting structure-borne noise in cross-laminated timber buildings during conceptual design

Seismic acceleration demands in tall CLT buildings, predictive models and intensity measures

An accurate prediction of floor accelerations is crucial for estimating damage to contents and non-structural components in a building. Oversimplifying the nature of acceleration demands might result in biased estimates of building damage and consequently bias in the calculation of economic losses. However, given the relative novelty of multi-storey tall timber buildings, dedicated studies and models of their seismic acceleration demands are lacking. The need for these is stressed further when we recognise that the behaviour of walled timber structures is decidedly different from that of other conventional structural types. In this study, we apply modern data-driven approaches to evaluate efficient intensity measures (IMs) and develop regression models for predicting the peak floor acceleration (PFA) of multi-storey cross-laminated timber (CLT) buildings. Twenty-four IMs are evaluated and their prediction performance is compared. The sensitivity of acceleration demands to different IMs over a wide range of CLT buildings is investigated. We perform a systematic feature selection process using three different data-driven techniques. The selected features are then used to develop nine regression models to estimate PFA. Various modelling techniques, consisting of conventional (Linear and Polynomial regressions) as well as machine learning algorithms (Decision trees, Random forest, K-nearest neighbour, and Support vector regression) are used. The dataset used to train the models is obtained from numerical results of 69 CLT building models with variations in building height, panel fragmentation levels, and q-factors (ductility levels) subjected to a large set of strong earthquakes. After assessing the accuracy of our model predictions, their PFA estimates obtained are compared against previous research and design codes. Finally, simplified expressions for estimating peak floor accelerations in CLT structures are provided for practical purposes.

The impacts of sustainable design practices and cross laminated timber structures on acoustic design

More projects in Australia are prioritizing sustainable design practices throughout their building life cycle. Environmental Sustainable Design (ESD) rating tools such as WELL, Green Star, and the Living Building Challenge (LBC) have existed for a decade or more, with some receiving wide adoption in Australia. These rating tools require the assessment of the ingredients, volatile organic compounds (VOCs), and embodied carbon of the materials specified on the project. In addition, cross-laminated timber (CLT) buildings are becoming a more attractive development option due to lower embodied carbon, a reduction in the structural requirements of the foundations, and an increased speed of construction. These sustainable practices are reviewed using a recent project example that combines these recent developments in sustainability: a commercial office fitout in a hybrid steel and cross-laminated timber structure that is targeting WELL Platinum and the Living Building Challenge. The challenges of specifying materials to meet sustainability targets, potential gaps in available products, and the acoustic design challenges of achieving high levels of sound insulation in cross-laminated timber structures are discussed. With a better understanding of sustainable design practices, acoustic designers can improve sustainability outcomes on all projects.

Seismic performance evaluation of self-centering balloon-framed CLT building

Balloon-framed cross-laminated timber (CLT) construction has a number of advantages when compared to platform-type construction; however, many international standards only include provisions for the latter as there is little research reported on the seismic performance of the former. In this paper, a seismic fragility assessment of a 4-storey balloon-framed CLT building in Vancouver, Canada, is presented. This structure is the first in North America that adopts a self-centering friction-based technology for the hold-downs (HDs). The seismic performance of the building was assessed by performing incremental dynamic analysis (IDA) on a three-dimensional finite element model using Cascadia Subduction Zone ground motions, and compared to a second building model with conventional dowel-type HDs. The analyses at the design intensity level showed that the self-centering building had an average maximum inter-story drift ratio of 0.67%, well below the 2.5% drift limit specified in the National Building Code of Canada. Based on the IDA and taking into account uncertainties, the building had a collapse margin ratio of 2.96 and a 5.2% probability of collapse at the design level. Compared to the conventional HDs, the friction-based HDs did not improve the building’s collapse capacity, but reduced the building drift by more than 20% at lower damage states, demonstrating the effectiveness of designing balloon-framed CLT structures with a resilient self-centering HDs in high seismic zones.

Dynamic identification and model calibration of connection stiffness in multi-storey cross-laminated timber buildings

Dynamic identification and model calibration of connection stiffness in multi-storey cross-laminated timber buildings

How can we combine urban cooling strategies to effectively cool cities over the entire diurnal cycle?

The urban heat island effect generally peaks in the night/evening hours and, in some cases, an urban cool island effect during daytime has been reported. These patterns are observed mainly because of the widespread use of impervious and thermally massive materials (like concrete and asphalt) in the built environment and their ability to store energy during the daytime and release it at night. Unfortunately, most urban cooling strategies, such as cool (white), green, and blue spaces, provide better thermal performance during the daytime than at night. Hence, such solutions are not ideal for nighttime heat mitigation. In this study, we investigate the effect of the thermal storage capacity of existing buildings on nighttime urban air temperature for a hot arid city—Phoenix, and a hot humid city—Atlanta. The study uses regional scale atmospheric modeling to compare the nighttime urban cooling capability of thermally light buildings (Cross-laminated timber buildings in this case) with concrete buildings. The results show that the adoption of thermally light buildings reduce nighttime air temperatures, and slightly increases daytime air temperatures. On the other hand, cool roof adaption could reduce urban air temperature significantly during the daytime and slightly at night. Therefore, together with cool roofs, thermally light buildings may be able to cool the surrounding air by an average of about 1 °C throughout the diurnal cycle, providing thermal comfort and reducing cooling demand during all hours.