Cross-laminated Timber Construction Research Articles

Longitudinal analysis of interorganizational collaborative networks of cross-laminated timber (CLT) construction

Purpose Cross-laminated timber (CLT) is an innovative construction material that provides a balanced mix of structural stiffness, fabrication flexibility and sustainability. CLT development and innovation diffusion require close collaborations between its supply chain architectural, engineering, construction and manufacturing (AECM) stakeholders. As such, the purpose of this study is to provide a preliminary understanding of the knowledge diffusion and innovation process of CLT construction. Design/methodology/approach The study implemented a longitudinal social network analysis of the AECM companies involved in 100 CLT projects in the UK. The project data were acquired from an industry publication and decoded in the form of a multimode project-company network, which was projected into a single-mode company collaborative network. This complete network was filtered into a four-phase network to allow the longitudinal analysis of the CLT collaborations over time. A set of network and node social network analysis metrics was used to characterize the topology patters of the network and the centrality of the companies. Findings The study highlighted the scale-free structure of the CLT collaborative network that depends on the influential hubs of timber manufacturers, engineers and contractors to accelerate the innovation diffusion. However, such CLT supply collaborative network structure is more vulnerable to disruptions due to its dependence on these few prominent hubs. Also, the industry collaborative network’s decreased modularity confirms the maturity of the CLT technology and the formation of cohesive clusters of innovation partners. The macro analysis approach of the study highlighted the critical role of supply chain upstream stakeholders due to their higher centralities in the collaborative network. Stronger collaborations were found between the supply chain upstream stakeholders (timber manufacturers) and downstream stakeholders (architects and main contractors). Originality/value The study contributes to the field of industrialized and CLT construction by characterizing the collaborative networks between CLT supply chain stakeholders that are critical to propose governmental policies and industry initiatives to advance this sustainable construction material.

Mechanical Characterization of Connections for Modular Cross-Laminated Timber Construction Using Underutilized Lumber

Mechanical Characterization of Connections for Modular Cross-Laminated Timber Construction Using Underutilized Lumber

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.

Development of laboratory experiments to determine critical moisture condition of CLT constructions

There is an increased interest in using Cross-laminated timber (CLT) in construction, but many buildings are erected without weather protection, which poses a risk of moisture impact if wood is exposed to precipitation during construction. The construction industry argues that there are no documented critical moisture levels for CLT and no specific test method. In the study, a laboratory test set-up was developed to study mould growth under realistic and controlled climatic conditions after exposure to distilled water and spore suspension. In the experiments, small test specimens of CLT structures were exposed to distilled water for 1 day or 1 week. During the development of the method it was found that exposed for one day and then given the opportunity for open drying did not give rise to mould growth. On the other hand, growth occurred on surfaces that could not dry immediately, for example at connection points. For specimens exposed for one week, mould growth arose regardless of whether the surfaces could dry immediately or not. The conclusions apply primarily to the climates studied. The methodology needs to be further developed, with other scenarios being studied, and calibrated against samples exposed to outdoor air, dust, dirt and rainwater.

Views of Cross-Laminated Timber (CLT) Manufacturer Representatives around the World on CLT Practices and Its Future Outlook

Due to its recent emergence, there is a limited body of global market research available on CLT. Presently, the literature lacks comprehensive understanding regarding the present state, varied uses, and future outlook of CLT construction at a global level. The objective of this article is to address this knowledge gap by conducting semi-structured, in-depth interviews with CLT manufacturer representatives around the world, including Austria, Italy, Czech Republic, Sweden, Norway, Finland, Japan, Canada, and Uruguay. Critical findings emphasized that (1) the predominant mention was about the insufficient knowledge and experience within construction professionals; (2) a clear need for heightened expertise and training in the domain of CLT was underscored; (3) CLT was regarded as a favorable choice in efforts to combat climate change; (4) CLT was deemed highly appropriate for settings marked by variable climatic conditions; (5) CLT producers, particularly those with comprehensive, vertically integrated operations encompassing the entire processing cycle, remained unaffected by the rise in raw material costs; (6) the COVID-19 pandemic generally yielded positive impacts on the CLT market; (7) primary application of CLT, as emphasized by most manufacturers, is in residential and institutional projects; and (8) most manufacturers noted the expansive and boundless opportunities within the market, especially considering the climate crises as potential future avenues for the utilization of CLT. This article aims to advance the widespread adoption of CLT within the global construction sector. It will achieve this by elucidating the obstacles, possibilities, and forthcoming prospects associated with CLT.

System Connector “Double Dovetail Tenon”—A Wood–Wood Based Alternative for Connecting CLT-Elements

In timber construction, there are still no standardized wall–ceiling system connectors made of wood for cross laminated timber construction (CLT). Based on experimental investigations of the bar-shaped dovetail connections, a wood–wood system connection was developed at the University of Innsbruck. First, the traditional dovetail connection for bar-shaped beam connections was investigated. The findings showed the high potential of force transmission in the flank area, especially for beam connections of the same height, where the height of the pre-timber is too small. To date, the load-bearing capacity of the flanks has not been taken into account in the calculation methods. To increase the force transmission paths in the base of the tenon, it was shaped in steps. This led to a load redistribution and thus delayed the failure of the connection. The knowledge gained formed the basis for an independent connecting element that resulted in the so-called “double dovetail”. The connector is a three-dimensional, statically effective double dovetail element. The wood system connector is made of block-glued laminated veneer lumber (LVL) and is manufactured in a CNC-milling process. The results of the tests showed the high performance potential of the LVL system connector, which can play an important role in future timber construction.

Construction details affecting flanking transmission in cross laminated timber structures for multi-story housing

The desire of the building developers to leave the surfaces of cross laminated timber constructions in multi-story housings visible for the building user, leads to acoustic problems with the flanking sound transmission that cannot be controlled by means of wall linings. As a result, controlling flanking sound transmission by measures directly in the joint is getting increasingly important. The main parameter for describing the vibrational power transmission over a junction between structural elements is the vibration reduction index Kij. For this quantity, some planning values are spread over numerous publications. None of the currently available data sources represents a holistic view on the building acoustic performance of the on the market available products for elastic interlayers and fasteners which are used in a wall-ceiling junction. The following paper shows results of measurements of vibration reduction indexes of different configurations of a wall-ceiling joint in a test facility. Different elastic interlayers and fasteners were investigated. The vibration reduction indexes spread from 16db to 26dB as a function of the joint configuration and the load applied on the joint. The measurement results obtained are discussed and the essential parameters for influencing the flanking sound transmission are worked out and quantified.

Bonding performance of cross-laminated timber-bamboo composites

Bamboo is one of the most important renewable resources in China, leading to the development of bamboo products as well. Alternative applications of bamboo need to be developed in the field of construction, especially in cross-laminated timber (CLT) construction, due to better mechanical performance of bamboo and the increasing popularity of CLT construction in recent years. The bonding performance of cross-laminated timber-bamboo (CLTB) composites fabricated with Spruce-pine-fir (SPF) dimension lumber and bamboo scrimber boards was investigated here. L9 (34) orthogonal experiments with four factors (adhesive type, adhesive spreading rate, clamping pressure, and clamping time) and three levels were applied to evaluate their impacts on the bonding indicators of CLTB through block shear and delamination tests. Results showed that adhesive type had the most critical influence on the bonding performance. The optimal manufacturing parameters were adhesive of phenol resorcinol formaldehyde (PRF), adhesive spreading rate of 250 g/m2, clamping pressure of 1.0 MPa, and clamping time of 420 min, respectively. PRF adhesive yielded higher block shear strength, wood failure percentage, and lower rate of delamination than one-component polyurethane (PUR) and emulsion polymer isocyanate (EPI), especially under wet or boiling condition.

Digital transformation in a cross-laminated timber business network

PurposeThe purpose of this paper is to investigate two current transformation processes in the construction industry: the adoption of a novel material, cross-laminated timber (CLT), and the enhancement of digital transformation. This paper depicts the actors and interaction in the business network that is emerging around CLT construction and, in particular, how digital transformation (that is, the deployment of Construction 4.0 solutions) occurs in this business network.Design/methodology/approachDigital transformation is a relatively new phenomenon in CLT construction, and the authors, therefore, adopt a qualitative inductive research approach and rely on semi-structured interviews.FindingsThe findings of this paper suggest that it is critical for actors to adopt an interorganizational perspective in CLT construction, instead of only focusing on internal operations. An interorganizational perspective supports successful CLT construction, as well as the deployment of Construction 4.0 solutions. This will bring about the benefits of digital transformation in the construction industry.Research limitations/implicationsThis paper investigates the network created around CLT construction in Finland but more generally illustrates the change toward Construction 4.0 solutions.Practical implicationsFor managers, this paper explicates the importance of networking, instead of focusing on the internal development of the company, when adopting novel solutions emerging from both construction and information technology-related advancements.Originality/valueStability and traditions are characteristic of the construction industry. New technical solutions and materials, together with calls for sustainability, have challenged the traditional ways of constructing, and for example, the development of CLT construction has led to an emergence of new business networks. This material-related process and the ongoing digital transformation of business form an interesting context for an empirical-based analysis of changing interaction and networks. This paper gives the first insights into how digital transformation can benefit the evolution of the network.

Cross-Laminated Timber: A Survey on Design Methods and Concepts in Practice

Cross laminated timber (CLT) is becoming increasingly popular in timber construction due to its versatility. However, its structural anistropy requires the application of particular concepts and design methods. The article on hand presents the results of a worldwide survey conducted among engineers working with this product. Thus, it presents the current state of knowledge and practice on CLT construction: an overview of the experience of engineers working with CLT design, the commonly used verification methods, and the implementation of the material properties and different required assumptions in the software. An outlook to design problems in complex design situations relevant for multi-storey buildings and potential research fields is indicated additionally. The general picture is quite heterogeneous, with little consensus on the assumptions, design methods or applied tools. A wide repertoire of different approaches based on a large range of literature is found in practice. This is in part the result of the current lack of standardisation and currently incomplete regulations. Future efforts should focus on these two aspects to increase the applicability of CLT globally and strengthen its competitiveness.

A building information modeling‐fire dynamics simulation integrated framework for the simulation of passive fire protection in a mid‐scale cross‐laminated timber compartment: Numerical implementation and benchmarking

AbstractConstruction fires are a big threat to worker safety and property safety. Mass timber buildings under construction are largely unprotected as they are not yet equipped with active fire protection systems. With the addition of Types IVA, B, and C, the 2021 International Building Code adopted stricter requirements for mass timber buildings that are under construction. Cross‐laminated timber (CLT) is used as the primary structural element for high‐rise mass timber buildings. However, to date, limited number of research studies investigated the impact of passive fire protection for CLT buildings that are under construction. To facilitate a better understanding of construction fires and their consequences, it is necessary to develop a numerical modeling solution for the early phases of a CLT construction project, which can be achieved by using building information models together with fire dynamics simulation (FDS). However, the numerical modeling technique must be benchmarked against experimental data first to then extrapolate the modeling technique to explore other parameters and conduct FDS analysis. Therefore, this paper develops and benchmarks a numerical modeling solution against a mid‐scale CLT compartment fire test by applying the FDS tool to simulate the fire behavior within the CLT compartment. The FDS analysis results are expected to validate the practicality of simulating the fire behavior in CLT structures using the numerical model proposed in this study. The overarching goal of this study is therefore to develop a comprehensive numerical modeling solution to simulate and assess passive fire protection sequencing in CLT buildings that are under construction.

Development of Creep Deformations during Service Life: A Comparison of CLT and TCC Floor Constructions

Cross-laminated timber (CLT) slabs in residential buildings need additional weight, e.g., in the form of screeds or gravel layers, to fulfill the criterion for the highest impact-sound class. The additional mass is, however, not exploited for the load bearing behavior, but adds additional weight and leads to an increased height of the floor construction. In this study, such a CLT floor construction with a construction height of 380 mm is compared with a composite slab consisting of a CLT plate with a concrete layer on top with a floor construction height of 330 mm. The timber concrete composite (TCC) slab has a different creep behavior than the CLT slab. Thus, the development of the time-dependent deflections over the service life are of interest. A straightforward hybrid approach is developed, which exploits advanced multiscale-based material models for the individual composite layers and a standardized structural analysis method for the structural slab to model its linear creep behavior. The introduced approach allows to investigate load redistribution between the layers of the composite structure and the evolution of the deflection of the slab during the service life. The investigated slab types show a similar deflection after 50 years, while the development of the deflections over time are different. The CLT slab has a smaller overall stiffness at the beginning but a smaller decrease in stiffness over time than the investigated TCC slab.

Possibilities of Useful Use of Glued Wooden Construction Residues.

People have erected buildings with the use of timber structures for a long time. The uses of timber constructions are very diverse—it is used for the production of exterior wall and roof constructions, window frames and doors, and it is used for dry as well as wet premises. Scandinavian countries have extremely vast experience of using timber structures. Latvia has a rather extensive timber processing and timber structure manufacturing sector. Many companies are involved in timber processing, however, to enable even more extensive use of timber structures, environmental and technically economic requirements of contemporary building must be taken into consideration. Environmental requirements for timber structures provide certain advantages in comparison to other building materials, but technically economic requirements are very important as well. The development of manufacturing of glued constructions and research of production processes of these constructions allows one to find solutions for the reduction in the cost of timber structures, and the results of such research can ensure significant development of the use of timber structures in building, as well as reduce total construction costs. The basic objective of the study is to investigate the residual materials arising as a result of processing cross-laminated timber constructions (CLT panels), material generated as a result of high levels of construction production, and research of the opportunities to reprocess the residual materials generated as a result of laminated timber structure manufacturing into materials suitable for production of building constructions. The majority of CLT panels are manufactured using 20, 30 and 40 mm thick boards, and, during the panel manufacturing process, there are various standard thicknesses of panels, for example, 60, 80, 100, 120, 140, 160 mm, etc. Various layers are used for the creation of various thicknesses depending on the necessary technical properties. Various arrangements of the thickness of a single panel will cause different structural and physical behaviour (i.e., impact of changes in moisture, fire resistance, etc.). During the research and for the purposes of testing of CLT panels, only residues with equal types and thicknesses of lamellae were selected. Two main purposes were included in the panel testing process: (1) Comparison of technical performance of the residues of CLT panels with the classic CLT panel. Curve strength and tensile strength tests were performed in accordance with LVS EN standards (LVS EN 16351: 2016 and LVS EN 408 + A1: 2012). All the samples were prepared according to the LVS EN standards. (2) To assess the impact of two resins (melamine urea formaldehyde (MUF) and polyurethane (PU)), widely used in industry, on structural properties of recycled CLT material. Results of the research show that recycling residues of glued wooden constructions may lead to good results, and manufacturing residues of CLT panels may be successfully used in construction and for the reduction in CLT panel manufacturing costs.

CLT construction without weather protection requires extensive moisture control

This study examines how cross-laminated timber (CLT) constructions, including joints, connections and attachment points, are affected by precipitation during construction. The case studies are based on moisture content measurements and material sampling as well as microbiological analysis during the structure’s construction stage. The study does not include remediation control. The field measurements show microbiological growth in all buildings and almost all floor structures that were investigated. Of a total of 200 measuring points analysed, half had mould growth and around a third had moderate or extensive growth. The moisture content measurements for one of the locations with the largest percentage of elevated or high moisture content was at the top of the floor structure in the bottom gap between timbers in the CLT top layer. This is one example of several materials or construction components where there is limited possibility of dry out. Based on the outcome, it would appear difficult, or impossible, to avoid the appearance of microbial growth during construction with CLT without weather protection. Previous studies indicate that microbiological analysis of CLT is extremely rare in both laboratory and field studies, which implies that there are obvious shortcomings in the scientific work. The fact that mould growth is often invisible needs to be disseminated, especially in practical studies. However, there seems to be a good level of awareness in the literature that theoretical studies often conduct mould growth risk evaluations. There do not appear to be any moisture safety assembly methods or solutions for CLT construction that do not have weather protection or a declaration of the critical moisture conditions for CLT products.

Developing a BIM and Simulation-Based Hazard Assessment and Visualization Framework for CLT Construction Design

AbstractOne emerging trend in sustainable medium-density construction is the use of mass timber products such as cross laminated timber (CLT), which is a novel approach that involves numerous conne...

Sustainable Cross-Laminated Timber Structures in a Seismic Area: Overview and Future Trends

Cross-laminated timber (CLT) buildings are recognized as a robust alternative to heavyweight constructions, because beneficial for seismic resistance and environmental sustainability, more than other construction materials. The lightness of material and the satisfactory dissipative response of the mechanical connections provide an excellent seismic response to multi-story CLT buildings, in spite of permanent damage to timber panels in the connection zones. Basically, CLT constructions are highly sustainable structures from extraction of raw material, to manufacturing process, up to usage, disposal and recycling. With respect to other constructions, the potential of CLT buildings is that their environmental sustainability in the phases of disposal and/or recycling can be further enhanced if the seismic damage in structural timber components is reduced or nullified. This paper reports a state-of-the art overview on seismic performance and sustainability aspects of CLT buildings in seismic prone regions. Technological issues and modelling approaches for traditional CLT buildings currently proposed in literature are discussed, focusing the attention on some research advancements and future trends devoted to enhance seismic performance and environmental sustainability of CLT buildings in seismic prone regions.

Cross-laminated timber constructions in a sustainable future – transition to fossil free and carbon capture technologies

Cross laminated timber (CLT) has recently increased in use as a building material for low carbon design and is often applied in small and multi-story buildings. Several studies have shown lower fossil related greenhouse gas emission than alternatives, but the life cycle emissions vary substantially between different CLT producers. These emissions are mainly indirect and thus climate change mitigation could reduce these emissions. Previous research shows that that biofuels and carbon capture and storage (CCS) are technologies that have the potential to reduce the climate impacts of the CLT life cycle. This study assesses the impacts on climate change from CLT with these technologies within the framework of environmental product declarations (EPD). In the short run, switching to fossil free fuels provides a reduction in the carbon footprint of CLT. In the long run, CCS at the end-of-life of CLT buildings can provide a net negative carbon footprint over the life cycle. This assessment on the use of CLT is mainly related to the Sustainable Development Goal SDG9 Industries, innovation and infrastructure and the indicator for CO2 emissions per value added, so the assessment in this paper is mainly focused on this goal. SDG7 on affordable and clean energy and SDG15 Life on land are also relevant.

Thermo-energetic performance of wooden dwellings: Benefits of cross-laminated timber in Brazilian climates

This research focused on studies of the cross-laminated timber (CLT) construction system and, in particular, on an innovative panel composition of eucalyptus (Eucalyptus grandis) heartwood, which is considered in Brazil as a low-added-value material that is often discarded or used for less noble purposes. The aim of this study was to investigate the thermo-energetic performance of CLT panels for use in low-income housing under several different climate conditions. The research was based on the simulation method of the Brazilian Technical Regulation of Quality for the Energy Efficiency Level of Residential Buildings (RTQ-R). The results, based on 72 parametric simulations, proved that CLT panels made of eucalyptus heartwood have significant potential for thermo-energetic improvement in various housing types under diverse climatic conditions. The simulated envelope combinations showed that in Curitiba (bioclimatic zone 1), it is important to associate 5-layered CLT panels with 10 cm thermal insulation; in São Paulo (bioclimatic zone 3), the envelope should be provided with low solar absorptance and 5-layered CLT panels without thermal insulation; and in Belém (bioclimatic zone 8), in addition to the low solar absorptance in the envelope, the CLT panels should be composed of only three layers and without thermal insulation. It was concluded that the innovative CLT construction system with low-added-value eucalyptus heartwood is a very promising technology for Brazilian dwellings that are more energy efficient, with further studies on mechanical behavior being necessary for its consolidation in the country.

Quantifying the Greenhouse Gas Emissions in the Construction of Wooden School Structures Using the Cross-laminated Timber Construction Method

Quantifying the Greenhouse Gas Emissions in the Construction of Wooden School Structures Using the Cross-laminated Timber Construction Method

Acoustical Properties of Southern Pine Cross-Laminated Timber Panels

Abstract Cross-laminated timber (CLT) is composed of a series of lumber layers placed orthogonally to create a thick panel. Advantages of CLT construction include reduced construction time, lighter...