Cross-laminated Timber Research Articles

Influence of screw angle and position on the extraction dynamics of Cross-Laminated Timber: an empirical analysis and comparative modeling study

ABSTRACT The design of dowel-type fastener connections is crucial for the structural integrity of Cross-Laminated Timber (CLT) systems, with individual fastener anchorage capacity as a key factor. This study investigates the withdrawal performance of Self-Tapping Screws (STSs) in CLT systems using Canadian Douglas fir. Four driving angles—45°, 60°, 75°, and 90°—were tested, alongside screw placements within panel gaps. Optimal performance was observed at 75° and 90°, with 90° placement in gaps enhancing stiffness and ductility but reducing energy dissipation. The ratios of experimental capacities to model predictions were 1.26–1.49 for the Blaß and Uibel (B&U) model and 1.36–1.56 for Eurocode 5 (EC5). The new EC5 code, compared to the previous version, includes several advancements such as more accurate material properties and improved calculation methods for fastener withdrawal capacity, offering enhanced prediction accuracy for STS performance in CLT. The discrepancies in the over-strength factors predicted by the new EC5 version ranged from 1.07 to 1.37. These findings suggest the need to consider the incorporation of a specific calculation model for STS withdrawal capacity in CLT, such as the Ringhofer et al. model, in the next revision of EC5.

Study on Smoke Leakage Performance in Mass Timber Construction Taking Cross-Laminated Timber Walls as an Example

In contemporary building design, partition walls combined with doors and windows are commonly used to control the spread of smoke. Understanding the smoke leakage characteristics of cross-laminated timber (CLT) walls is crucial for enhancing safety. This study investigates the smoke-sealing performance of CLT walls through full-scale tests, focusing on the application of this type of mass timber construction in smoke control. The test specimens included four joints, with leakage measured under two conditions—non-fire and fire exposure—at three different pressure differentials. A total of 72 tests were conducted. The results showed that under non-fire conditions, the leakage rate was 0.00 m³/h, while exposure to fire caused a significant increase in leakage. Under a pressure differential of 25 Pa, the average leakage rate was 8.17 m³/h, with a maximum of 8.27 m³/h. This study also proposes a method for evaluating the leakage rate of a single joint, which helps estimate the smoke layer descent time and, in turn, the allowable evacuation time. The findings not only enhance the fire safety performance of mass timber construction but also provide valuable insights for evacuation planning.

Out-of-plane bending and shear behavior of cross-laminated bamboo and timber under four-point loading with variable spans

This paper investigates the out-of-plane four-point loading behavior of cross-laminated bamboo and timber (CLBT) with variable spans. The experimental design involved CLBT specimens with spans ranging from 1800 mm to 3600 mm, and cross-laminated timber (CLT) specimens were used as the control. Theoretical calculations and finite element simulation methods were employed to analyze the out-of-plane loading performance. The results indicated that under the same span, the measured mechanical properties of CLBT specimens were higher than those of CLT specimens. For example, the CLBT specimens with a span of 3600 mm exhibited bending strength and global bending stiffness that were approximately 190 % and 70 % higher than those of the CLT specimens, respectively. Increasing the span reduced internal shear stress in both CLBT and CLT specimens and increased their strength and global stiffness in bending. Although the CLBT floor panel was heavier than that of the CLT floor panel, it exhibited lower mid-span deflection in the serviceability limit state, indicating better performance in safety and stability compared to CLT. The results of this study offer valuable insights into the design and application of CLBT floor panels.

Dynamic and quasi-static evaluation of stiffness properties of CLT: longitudinal MoE and effective rolling shear modulus

Cross-Laminated Timber (CLT) is an engineered wood product composed of solid layers of glued sawn timber. In this study, essential material stiffness parameters for CLT made from Norway spruce and Scots pine are evaluated. Specifically, the longitudinal modulus of elasticity (MoE) for longitudinally oriented layers and the effective rolling shear modulus for transversely oriented layers are the focus. By combining finite element (FE) analysis with four-point, out-of-plane bending tests using digital image correlation (DIC), a robust assessment of the effective rolling shear modulus of CLT layers is achieved. Additionally, eigenvalue analysis, applied to an FE model, along with resonance frequencies obtained from dynamic excitation of CLT, enables stable and simultaneous assessment of the dynamic longitudinal MoE and effective rolling shear modulus. Notably, while the dynamic MoE of longitudinal CLT layers is only 4% higher than the quasi-static local MoE, the dynamic effective rolling shear modulus of CLT layers is 40% higher than the quasi-static effective rolling shear modulus. This finding indicates a tangible viscoelastic behavior of wood concerning rolling shear.

Analytical Solutions for Thermo-Mechanical Coupling Bending of Cross-Laminated Timber Panels

This study presents analytical solutions grounded in three-dimensional (3D) thermo-elasticity theory to predict the bending behavior of cross-laminated timber (CLT) panels under thermo-mechanical conditions, incorporating the orthotropic and temperature-dependent properties of wood. The model initially utilizes Fourier series expansion based on heat transfer theory to address non-uniform temperature distributions. By restructuring the governing equations into eigenvalue equations, the general solutions for stresses and displacements in the CLT panel are derived, with coefficients determined through the transfer matrix method. A comparative analysis shows that the proposed solution aligns well with finite element results while offering superior computational efficiency. The solution based on the plane section assumption closely matches the proposed solution for thinner panels; however, discrepancies increase as panel thickness rises. Finally, this study explores the thermo-mechanical bending behavior of the CLT panel and proposes a modified superposition principle. The parameter study indicates that the normal stress is mainly affected by modulus and thermal expansion coefficients, while the deflection of the panel is largely dependent on thermal expansion coefficients but less affected by modulus.

Compensated velocity feedback for non-collocated active vibration control

AbstractThis paper addresses non-collocated vibration control of multi-modal structures such as plates. The challenges of applying this non-collocated configuration in real systems are tackled by proposing a second-order compensator using velocity feedback control. The compensator design aims to use uncontrolled data only, where its parameters are obtained from a measurement of the point-frequency response function at the actuator attachment point (anti-resonance assignment). Compared to other control strategies such as optimal control, no plant model or state estimation is required in the hardware implementation of the controller, making this approach relatively simple. The compensator design is outlined for a generic three-degree-of-freedom system, as its simplicity allows for deeper investigation of the effects of the compensator itself. The proposed design is then experimentally validated by vibration control of a cross-laminated timber panel, considering three closely spaced natural frequencies. Further difficulties encountered in dealing with real world systems are discussed by comparing experimental data with simulations. To achieve this, a model of the electromechanical system composed of the panel and two electrodynamic shakers is used. The parameters of the compensator for the system are then obtained and a sensitivity study to these parameters is carried out by calculating a control performance taking into account filters and the effects of time delay.

Application of laminated and cross-laminated timber in reconstruction and new construction

The article is devoted to the actual problem of restoration of construction objects of Ukraine destroyed as a result of military actions. The issue of manufacturing and effective application of cross-laminated timber panels and other products made of laminated timber for use in recon-struction, restoration of damaged construction objects and new construction is considered. Why can the availability of the raw material base, its renewability and ease of extraction and processing contribute. Cross-laminated timber is a relatively new building material based on timber, which is an array of boards laminated in layers in a mutually perpendicular direction. The layers of lumber are laminated together under pressure, forming a virtually monolithic slab. The production of cross-laminated timber solves one of the important problems, namely the use of small and medium-sized cross-sections of boards to create large arrays, which allows you to signifi-cantly save commercial timber. The main advantages of laminated and cross-laminated timber as building materials are given and the feasibility of their application for buildings and structures of various functional purposes is proven. Examples of modern high-rise buildings con-structed using cross-laminated timber panels around the world are presented. Due to the elimination of some of the defects of whole timber and the preservation of one of the main advantages, namely, low weight with relatively high strength values, laminated and cross-laminated timber can become one of the main materials for the development of new areas and the restoration or reconstruction of damaged ones as a re-sult of military actions, buildings and structures of various purposes. The low weight of structures made of laminated and cross-laminated timber will reduce the cost of strengthening existing structures and the cost of ma-terials for new foundations in the case of new con-struction by at least 30% in comparison with houses erected using more traditional methods - these materials.

Analysis of existing studies on wood under impact and ballistic loads

Wood is one of the oldest building materials. However, with the advent of the industrial revolution, metal and reinforced concrete structures have almost completely displaced wood from the market of basic building materials. At the same time, wood is widely used in the manufacture of furniture, decoration, floors, auxiliary structures, etc., and this applies to all spheres of human life and everyday life. A separate niche is occupied by wood asa material for fortifications, as the most accessible. Studies of the ballistic characteristics of wood are most relevant in forensics, due to the fact that bulletsfired in urban conditions very often hit wooden objects [1].The war unleashed by the Russian Federation in Ukraine forces engineers to look for the most rational materials for the construction of buildings forboth civilian and military purposes. And in this case, wood can be a competitive material along with concrete and steel, given the fairly good ability of woodto absorb energy. Certain types of wood are considered impact-resistant, so beech is used for the manufacture of hammer heads [3]. In addition to solidwood, there are quite a large number of wood-based materials, such as: glued wood, cross-laminated timber, glued veneer lumber and many others.These materials are already widely used in the construction of both low-rise and multi-story buildings. The properties of these materials for the perceptionof vertical and horizontal loads have been actively studied since the 1960s. However, the characteristics of impact strength and ballistic properties ofthese materials have hardly been studied. This paper considers the state of modern research on the ballistic properties of wood and materials based on it with the prospect of further research and use in engineering protection structures.

Longitudinal Shear in Timber-Concrete Composites with Flexible Adhesive Connections-Experimental and Numerical Investigations.

Timber-concrete composites are established structural elements to combine the advantageous properties of both materials by connecting them. In this work, an innovative flexible adhesive connection in different configurations is investigated. Load-bearing capacity, stiffness, and the failure modes were first experimentally investigated by performing push-out tests. Subsequently, a numerical evaluation using ABAQUS 2017/Standard software was carried out in order to develop a three-dimensional numerical model. The Cohesive Zone Model (CZM) is employed to represent the adhesive characteristics at the contact areas between the Cross-Laminated Timber (CLT) and concrete elements. Three different connection configurations were evaluated, each consisting of five push-out specimens. The study investigates the impact of bonding surface area and the alignment of prefabricated glue strips with the load direction on the connection's longitudinal shear load-bearing capacity, stiffness, and slip modulus. In addition, the impact of cyclic loads and the impact of time on displacements were analyzed. The average load capacity of the full surface connection (type A) is 44.5% and 46.2% higher than the vertical adhesive strips (type B) and the horizontal adhesive strips (type C), respectively. However, the initial stiffness of the tested joints depends on the orientation of the prefabricated adhesive fasteners, being approximately 20% higher when the bonding elements are aligned parallel to the load direction compared to when they are oriented perpendicularly.

Deflection to natural vibration frequency ratio in a three-layer CLT slab with variable thickness of layers

This study examines the relationship between the maximum deflection and natural frequency of vibration in a three-layer cross-laminated timber (CLT) board at variable thicknesses of the inner and transverse plank layers under different boundary conditions. The finite element method (FEM), implemented in the SCAD++ computer complex by creating a finite element computational model in the form of a composite plate with anisotropic properties of the layers and rigid bonds between the plates, was used for the investigations. As a result, the values of maximum deflections and natural vibration frequencies for plates with different cross-sectional parameters were obtained. The obtained results are compared with the analytical values of the fundamental dependence obtained by Professor V.I. Korobko describing the relationship between the maximum deflection of a composite plate and the frequency of natural vibrations. It was found that the deviation of the numerical values of the K coefficient does not exceed 3% under different boundary conditions of structures and parameters of their cross-section.

Effect of crack defects on interlaminar shear properties of cross-laminated timber (CLT)

ABSTRACT Cross-laminated timber (CLT) has become one of the most popular engineering wood products in construction because of its excellent physical and mechanical properties. In this study, the short-span three-point bending test combined with acoustic emission test was used to study the effect of cracks on the inter-layer shear properties and fracture path of CLT. Crack length and crack location was used as influencing factors. Macro and micro failure patterns are analysed. The results show that the crack length had significant effects on the interlaminar shear strength and the initial failure load. The load-strain curve and acoustic emission location fracture paths were characterised by a rolling-shear failure stage, an instability stage, and a tensile failure stage of the tensile-side outer layer of the CLT. With the increase of crack length, the initial-failure load and inter-layer-shear strength were reduced due to the variations of crack-initiation location and crack-propagation path. The research of this study has certain guiding significance for the safe use of CLT in practical engineering.

Assessing the effectiveness of cross-laminated timber (CLT) roof assembly moisture control and mitigation strategies: A field laboratory

Exposure to moisture and wetting is a concern in mass timber construction and service. Understanding the moisture conditions and the drying response of mass timber during construction and service can impact durability of the building material and occupant health because of the potential for biological degradation and mould growth, respectively. Cross-laminated timber (CLT) used in roof assemblies is particularly susceptible to high moisture loading from exposure to driving rain and extended periods of ponding and water retention on roofs during construction. The field research conducted in this study utilises a purpose-built CLT test facility in Toronto, ON to test and assess the impact of three specific moisture control strategies towards both mitigating moisture and increasing the dry-out rate of CLT used in roof assemblies. The moisture control strategies tested were: (1) the integration of an air cavity directly above the CLT within the roof assembly, (2) the protection of CLT during exposure and moisture loading periods on site, and (3) the permeability of membranes installed in the roof assembly and during site exposure. The CLT roof panels underwent four months of exposure to exterior environmental conditions followed by two months of bulk water inundation at the CLT test facility site immediately prior to installation and enclosure. Moisture content was monitored at evenly distributed depths in the CLT panels throughout exposure and inundation periods and for one year of simulated service conditions, post-enclosure. Comparative analysis of the moisture control strategies tested during this field laboratory demonstrate that the presence of an air layer above the CLT in the roof assembly consistently doubled the dry-out rate compared to the assemblies without an air cavity. The results also found that unprotected CLT panels took approximately 2.5 times longer to dry-out to below 15 % MC than protected panels and finally, that in comparing the results of using impermeable vs. permeable air/vapour barrier membranes on the surface of exposed CLT, that the impermeable membrane slowed the dry-out rate of wetted CLT by approximately 20 %. The results of this research support the implementation of specific moisture mitigation and control strategies during design and construction towards promoting rapid dry-out of CLT in roof assemblies in service.

Physical and Mechanical Properties of Hardwoods Cross-Laminated Timber

Abstract Cross-laminated timber (CLT), a type of engineered wood product, is becoming widespread in the construction sector, especially for large commercial buildings. The increased demand for CLT is due its perceived benefits over conventional building materials. To effectively utilize the numerous benefits of this modern building material, there is need to ascertain its reliability as a structural material without affecting its serviceability. Thus, the objectives of this study were to evaluate both the physical and mechanical properties of CLT and to compare the mechanical properties of CLT manufactured with hardwood of low-grade lumber and industrially made softwood CLT. Hardwood species used to manufacture CLT panels were red oak (Quercus spp.), yellow poplar (Liriodendron spp.), and sweetgum (Liquidambar spp.). Commercially manufactured southern pine CLT panels were used as control. The evaluation of density was done at a moisture content of 12 percent. All specimens were mechanically tested in accordance with ASTM D198 to determine the modulus of elasticity (MOE) and modulus of rupture (MOR). The range of values for both MOE and MOR found in this study are not significantly different from values reported in a previous study. Of the hardwood samples tested, 95 percent had MOE greater than minimum allowable MOE of 1.2 × 106 psi (8,274 MPa) specified for softwood CLT by the American National Standards Institute/The Engineered Wood Association performance-rated CLT. Thus, the average MOE values observed for all the CLT species can be used as a basis for design values in the construction industry for hardwood species.

The Properties of Cross Laminated Timber (CLT): A Review

The Properties of Cross Laminated Timber (CLT): A Review

Cross-Laminated Timber Panels Produced by Low-Grade Yellow-Poplar Sorted by Nondestructive Evaluation

Abstract To manufacture and market a uniform and consistent product, the US lumber industry developed grading rules to classify their lumber. Visual grading is the most commonly applied grading system, although nondestructive evaluation (NDE) could be applied. Therefore, the objective of this research was to evaluate cross-laminated timber (CLT) panels produced from yellow-poplar (Liriodendron tulipifera) lumber sorted by NDE and compare their bending properties in the major direction to standard published panels by the American National Standards Institutes/The Engineered Wood Association (ANSI/APA) PRG 320-2019. Ten panels were produced with dimensions of 3.75 inches thick by 18 inches wide by 120 inches long. Flatwise bending, shear block, and cyclic delamination tests were performed following ANSI/APA PRG 320-2019. The results of the bending tests indicated that the calculated characteristic values using NDE-sorted lumber resulted in a 19 percent higher bending strength (Fb) than published values in ANSI/APA PRG 320-2019 for stress-rated lumber (E1 and E4) and 35 percent higher than visually graded yellow-poplar CLT panels reported by Azambuja et al. However, the modulus of elasticity (MOE) values (1.56 by 106 psi) were lower than those listed for E1 and E4 type panels. The adhesive evaluation showed delamination in some samples located in the outer areas of the panel, indicating that proper adhesion is possible with improvements in the panel production process used in the research. Overall, the results suggest potential opportunities to utilize yellow- poplar lumber that does not meet a visual structural grade category under Northeastern Lumber Association Manufacturers’ rules by classifying and sorting the lumber according to static MOE (MOEs) values assessed using NDE.

MICRO-MESO CHARACTERIZATION OF PREFABRICATED CONCRETE-CLT ADHESIVE JOINTS

This study evaluates the use of five commercially available epoxy adhesives (EAs), from low to high cost, as a connection alternative of timber-concrete composites (TCCs) using cross-laminated timber (CLT) and medium-strength precast concrete (25MPa). Five alternative EAs were initially evaluated via pull-off tests to determine the adhesive strength of the interface CLT/concrete, with average results varying from 0.6MPa to 3.6MPa. Subsequently, optical and scanning electron microscopy analyses were implemented to assess the microstructure of post-tested TCC specimens, finding that usually the CLT/concrete interface was not fully glued by the EAs and that there was a positive correlation between the penetration of each EA with the corresponding tension strength of the TCCs. Then, the three EAs with the largest adhesive strengths were further tested by small double-shear (SDS) tests evaluating their shear strength and deformation, as well as damage evolution and failure modes, which were obtained using digital image correlation. The SDS test average results ranged from 2.4MPa to 8.8MPa, and the EA with the best behavior was not the one with the highest tensile strength, but rather with the highest EA penetration into concrete, demonstrating that this property highly positively impacted the shear strength of TCCs. Finally, cost/benefit analyses were obtained, and interestingly, the EA with the best adhesive/shear performance was not the most expensive alternative, opening the discussion that, even though mostly expensive EAs have been used in TCCs, the option of technically valid and low-cost EA is feasible.

Experimental and numerical investigations on the impact of openings on the stiffness of CLT shear walls

Cross-laminated timber (CLT) exhibits high in-plane strength and stiffness, positioning it as a viable material for shear walls in seismic regions. However, the influence of openings on the in-plane stiffness of CLT shear walls remains inadequately studied. In this study, 43 CLT shear walls with different opening sizes were tested under in-plane loading. The stiffness reduction was less than 29% for openings 800×800mm (53% of panel width), but exceeded 60% for openings 1200×1200mm (80% of panel width). When assessed with identical opening sizes, 139mm and 175mm thick CLT shear walls displayed consistent stiffness reductions. Panels with an aspect ratio of 3:1 exhibited a more pronounced drop than 2:1 aspect ratio panels. A validated 3D finite element model was used to investigate the influence of panel layup and opening shape and location on the in-plane stiffness reduction. For a distance between the opening and panel edge exceeding 300mm, the shape and location of openings exerted negligible effects. Finally, the Dujič’s model was shown to be a suitable predictor to evaluate the in-plane stiffness reduction of CLT shear walls with openings.

Experimental Study on the Quasi-Static Cyclic and Dynamic Performance of Two-Story Platform Cross-Laminated Timber Mock-Ups

Experimental Study on the Quasi-Static Cyclic and Dynamic Performance of Two-Story Platform Cross-Laminated Timber Mock-Ups

Analysis of normal and shear stresses and vertical displacements in cross-laminated timber panels through plate theories, numerical and simplified methods

Resumo Amadeira lamelada colada cruzada (MLCC) é um produto empregado na forma de painéis que apresenta como desafio a consideração conjunta da disposição ortogonal de lamelas com o comportamento ortotrópico da madeira. Para avaliar o comportamento mecânico de painéis de MLCC, em flexão simples, é possível recorrer a teorias de placas, métodos numéricos e simplificados. Dentro desse contexto, este trabalho se propôs a analisar as tensões, normais e de cisalhamento, bem como os deslocamentos verticais em um dado painel de MLCC por meio de três teorias de placas, três métodos simplificados, método dos elementos finitos e um método analítico proposto. Para o estudo, foi considerado um painel de MLCC com cinco camadas de 20 mm de espessura, inicialmente quadrado com lados de 3 m, sendo, posteriormente, realizadas análises paramétricas da razão entre as dimensões em planta. Com as análises estruturais, foi possível a obtenção das tensões, bem como os deslocamentos verticais do referido painel. As análises paramétricas realizadas permitiram averiguar a sensibilidade do painel de MLCC proposto, em termos de tensões e deslocamentos verticais, frente às variações da razão entre as dimensões em planta do painel.

Enhancing CLT construction – Hygrothermal modelling, novel performance criterion, and strategies for end-grain moisture safety

This study validated a 2D dynamic anisotropic hygrothermal simulation model for Cross-Laminated Timber (CLT), focusing on vertical water uptake and moisture dry-out processes. The simulations, compared against experimental data, showed a root mean square deviation of ≤3.3 across all locations. Variations in material properties necessitated the use of multiple material definitions. Moisture storage and liquid conductivity function had a significant impact on the results. A new two-step moisture content (MC) performance criterion was developed: MC ≤ 16 % at 30 mm and MC ≤ 25 % at 10 mm from the end grain to prevent mould growth. Sensitivity analysis suggested that validating MC30 mm is reasonable when MC10 mm exceeds 19 %. The criterion was applied to analyse moisture management strategies for CLT end-grain moisture safety. Simulations with 30-year climate data indicated a slight decrease in successful outcomes in recent years. Strategic installation timing, particularly favouring the spring season due to its relatively drier conditions in Estonia, was found to be highly beneficial. CLT end-grain protection or full-coverage weather protection is recommended to ensure a high level of moisture safety, and long construction periods should be avoided even with full-coverage protection. Including moisture dry-out periods before covering CLT is advised. However, unassisted dry-out is feasible only during spring (up to four weeks). Additional equipment is necessary for timely moisture dry-out during other seasons, including summer, due to higher precipitation loads. The use of anisotropic 2D hygrothermal simulations proved to be practical in enhancing CLT resilience to moisture-induced damage.