Engineered Wood Products Research Articles

Adhesive free Melaleuca rhaphiophylla (Swamp Paperbark) bark as an engineered wood product

Adhesive free Melaleuca rhaphiophylla (Swamp Paperbark) bark as an engineered wood product

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.

X Ray Based Laboratory Testing Methodology for Panel Products against Termite Resistance

A host of new eco- friendly preservatives and treatments for protection of panel products are being developed. Engineered wood products require extra caution while testing with termites, due to high moisture conditions during field tests, a composite panel may subject to delamination making it difficult for a proper rating and determination of damage due to termite activity. This work focuses on development of a laboratory testing method for plywood and blockboard resistance against termite species Heterotermes indicola and Coptotermes heimi. The termite species preferability test was done in order to find out the most palletable wood species. Pinus sp and Mangifera sp. were found to be the most palletable wood species and were taken as control. Determination of maximum vigorous activity of both the termite species were done by monitoring wood consumption and survival, and it was found that Heterotermes indicola showed highest survival at population density of 0.004 g/ml, whereas Coptotermes heimi showed highest survival at population density of 0.0008 g/ml. A non-destructive and quantitative approach of X-Ray analysis was adopted for result evaluation for more quantifiable result than traditional visual observation. Based upon the results obtained, a termite testing methodology was developed for wood based panel products such as plywood and block board.

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.

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.

A Fast-Calibrated Computational Fluid Dynamic Model for Timber–Concrete Composite Ventilated Façades

Timber–concrete composite (TCC) systems join the positive aspects of engineered wood products (good seismftaic behaviour, low thermal conductivity, environmental sustainability, good behaviour under fire if appropriately designed) with those of concrete (high thermal inertia, durability, excellent fire resistance). TCC facades are typically composed of an internal insulated timber-frame wall and an external concrete slab, separated by a ventilated air cavity. However, there is very limited knowledge concerning the performance of TCC facades, especially concerning their thermal behaviour. The present paper deals with the development and optimization of a 2D Computational Fluid Dynamic (CFD) model for the analysis of TCC ventilated façades’ thermal behaviour. The model is calibrated and validated against experimental data collected during the annual monitoring of a real TCC ventilated envelope in the north of Italy. Also, a new solver algorithm is developed to significantly speed up the simulation (i.e., 45 times faster simulation at an error below 3.5 °C compared to a typical CFD solver). The final model can be used for the time-efficient analysis (simulation time of approximately 23 min for a full day in real-time) and the optimization of the thermal performance of TCC ventilated facades, as well as other ventilated facades with external massive cladding. Our simulation strategy partially avoids the expensive and time-consuming construction of mock-ups, or the use of comparably slow (conventional) CFD solvers that are less suitable for optimization studies.

Shear performance of glued and screwed timber-steel composite connections for composite timber-steel beams

Mid- to high-rise mass timber buildings gained popularity in the last decade. Yet, engineered wood products (EWPs) used to erect these buildings have structural limitations. EWPs present brittle failure modes, particularly in bending, shear and tension, and have a low modulus of elasticity resulting in shorted spans and deeper beams relative to those in the steel and reinforced concrete counterparts. Timber-steel hybrid beams represent a potential sustainable solution to overcome these limitations by taking advantages of the high strength, stiffness and ductility of steel, and the high capacity to weight ratio of timber. However, for this solution to be structurally performant, it is essential to create effective composite action between the two materials. This study therefore compares the structural efficiency of various bonding techniques between the steel and the timber materials. Two sets of assembly solutions, representing four connection types, were proposed and experimentally investigated: (1) connecting an embedded steel plate into the timber elements by using either polyurethane (PUR) structural adhesive with two manufacturing variations or 14 G×75 mm heavy duty screws, and (2) connecting a steel plate on the surface of the timber element using either PUR structural adhesive with self-tapping M4×40 mm screws or only self-tapping screws. Softwood Laminated Veneer Lumbers (LVL) and Grade 350 steel plates were used in the experimental tests. All bonding techniques were tested in shear. The shear capacity, the slip stiffness and the failure mode were evaluated. Additionally, the efficiency of the proposed manufacturing solutions was quantified by analytically evaluate the effective bending stiffness of a timber-steel composite beam manufactured with different bonding techniques being investigated. Results indicated that the glued connections allowed a significantly more efficient composite action, with failure occurring in the timber instead of at the composite interface and near-full composite action was reached, than the screwed connections. To achieve high composite action with the screwed solutions, a large number of screws was needed which may incur high manufacturing costs.

Board assignment heuristics for nail laminated out-of-grade timber

ABSTRACT Structural sawn timber, sourced from softwood plantations, is widely used in lightweight timber-framed residential housing and in engineered wood products for contemporary mass timber construction. However, a significant proportion of milled timber boards are considered ‘out-of-grade’, failing to attain a structural grade under existing classifications systems due to various stiffness, strength, and/or utility-limiting features. This study investigates the potential of controlled lamination techniques to produce structurally usable laminated timber products from out-of-grade timber, using a minimal number of requisite boards. Numerical and experimental methods were employed to compare different board assignment heuristics, in terms of reducing the stiffness variability in laminated board populations. The results indicate that controlled board locations produced remarkably consistent laminated products, achieving very low variability even with a minimum lamination of only two boards. The findings of this paper suggest that controlled lamination techniques have the potential to transform low-value out-of-grade timber into a valuable resource for value-added applications, challenging the existing market perception that out-of-grade timber lacks structural usability.

A systematic literature review of life cycle sustainability assessment of mass timber in the construction industry toward circular economy

AbstractLife cycle analysis has been used to evaluate the environmental impacts and economic costs of a range of engineered timber structural materials as well as other materials such as steel and concrete over the last two decades. This study presents a bibliometric analysis and systematic critical review by investigating the life cycle sustainability assessment (LCSA) of engineered timber products. LCSA is comprised of three main pillars namely, environment, cost, and social impact. The study compares alternative engineering wood products used in building structures such as columns, beams and wall surfaces. The geographical distribution, main sources of research, co-occurrence of keywords were analyzed for 93 peer-reviewed articles and conferences. The United States was the most productive country, contributing almost 23 documents. Australia was next with 12 publications. Most studies compared the LCA and LCC of alternative Mass timber products and concrete or steel. Most studies evaluated cross laminated timber (62%), followed by glued laminated timber (17%), and laminated veneer lumber (9%). A comparison of the economic and environmental aspects indicated that the social aspect are less considered. The review showed that the global warming potential of manufactring1 M3 of cross laminated timber is about 155.6–158.6 kg CO2eq. The majority of the publications reviewed focused on LCA whilst others focussed on the LCC of Mass timber. No research on social life cycle assessment has been conducted as yet. A framework is suggested for future research to identify the best alternative for engineering wood.

Cold temperature effects on the impact behaviour of glued-laminated timber beams

Engineered wood products, such as glued-laminated timber (glulam), have been and are continuously being utilized in the construction of tall timber buildings and notable landmark bridges. This infrastructure, particularly the latter, may be exposed to hazardous impact loads throughout their service life. As little research has been conducted on the impact behaviour of glulam beams under cold temperature conditions, there is a need to investigate the potential effects of impact loading on glulam structural elements at cold temperatures. This paper presents an experimental investigation aimed at understanding the effects of cold temperatures on the impact behaviour of glulam timber beams. Fifteen glulam beams were tested under quasi-static and impact loading, under ambient and cold temperatures. Drop weight impact testing was performed to simulate dynamic loading conditions similar to those experienced in real-world scenarios. The results indicate that both the loading regime and cold temperatures have a significant influence on the strength and stiffness of glulam beams, whereby statistically significant increases in the moduli of rupture and elasticity were observed, however, no interaction between the two variables occurred. A single-degree-of-freedom (SDOF) model was developed and validated using the experimental test results and found to provide good accuracy.

Performance Assessment of Wood-Based Composite Materials Subjected to High Temperatures

This paper is based on research placed within the broader framework of the growing environmental impact requirements of building materials. Given this context, wood-based composite materials have emerged as a promising and innovative solution for structural elements. The current work aims to define a system for testing the mechanical behavior of glued laminated timber elements when exposed to high temperatures, in the neighborhood of the pyrolytic decomposition of materials. These tests monitor the transient behavior of the composite material and characterize the parameters involved in the thermo-mechanical analysis of elements constructed using this type of engineered wood product. The tests are used for the calibration of the material models involved in the numerical analysis and for the analysis of potential prototypes, considering the transient thermal load and heat propagation through the materials. By taking such tests, benchmark models and laboratory procedures are defined that can be used in the future to evaluate different materials, existing or new, and material combinations used to construct such a composite.

Mechanical properties and probabilistic models of wood and engineered wood products: A review of green construction materials

Wood and engineered wood products are green construction materials with excellent mechanical properties, widely utilized in various buildings and bridges. This paper reviews their short-term and long-term mechanical properties and probabilistic models. Short-term mechanical properties analysis reveals strong tensile (up to 165 MPa) and bending strengths (up to 264 MPa), contrasted by lower compressive strength (up to 103 MPa) and minimal shear/rolling strength (up to 14 MPa). These properties vary based on species type, lay-up angle, and dimensions, and are mutually influential. It also demonstrated that innovative techniques such as compression and cross-laminated lay-ups enhance the strength and sustainability of wood products, utilizing smaller logs effectively and reducing carbon emissions. For long-term mechanical properties, empirical models typically used for creep strength assessment fail to account for load duration variability, a gap partly addressed by damage accumulation models which require further development. The considerable time for long-term tests underlines the need for developing accelerated load tests to more effectively assess durability. As for probabilistic models, numerical methods and machine learning provide advanced probabilistic models by analyzing extensive data, offering significant improvements over traditional experimental methods.The global contribution of the work is mainly to enhance the understanding of wood and engineered wood products for properly design and extensive application of timber structures in civil engineering and promoting sustainable development.

Fragility functions for low‐damage post‐tensioned timber frames

AbstractThe growing concern over environmental impact and the significant improvement in the quality of engineered wood products have led to the rapid growth of the timber building industry in the last decades. Although traditional, yet recent, mass timber structural systems, such as cross‐laminated timber walls, can provide satisfactory seismic performance during earthquakes in terms of life‐safety, the crucial need for more resilient timber buildings has prompted the development of low‐damage high‐performance self‐centring and dissipative solutions based on unbonded post‐tensioned hybrid connections, referred to as Pres‐Lam technology. The flexibility of design and construction speed, combined with the enhanced seismic performance, create a unique potential towards an earthquake‐proof sustainable building system. Despite the growing popularity of the technology, a comprehensive framework for the fragility analysis, to be used in risk and loss modelling applications, has not yet been developed for both component and building levels.This article aims to develop a framework for assessing the fragility curves of moment‐resisting Pres‐Lam frame systems, at both structural system and connection levels, by using and comparing different approaches that involve nonlinear static (pushover) and time history dynamic analyses. A Python‐based parametric workflow was developed to evaluate fragility curves for a wide range of case‐study buildings. Particularly, three distinct structures were selected, and their fragility curves were evaluated utilizing alternative methodologies at a building structural‐system level. Finally, fragility models were fitted for individual structural connections using the results of time‐history analyses. These models are intended for use in a component‐based loss assessment.

Numerical investigation on flexural performance of dowel laminated timber with laminas made of laminated veneer lumber

Horizontal dowel laminated timber (H-DLT) is a doweled engineered wood product with laminas made of solid timber. H-DLT has excellent bending resistance. However, the height of cross-section of H-DLT as a beam is limited by the width of solid wood laminas. Laminated veneer lumber (LVL) is an engineered wood product formed by hot-pressed gluing thin veneers, which is flexible in cross-section size compared to solid timber. Horizontal dowel laminated veneer lumber (H-DLVL) was developed by utilizing the H-DLT production methods and LVL material characteristics. H-DLVL has flexible size and good mechanical properties, and it can be made into beams and panels with large cross-sections. In this paper, the flexural performance of H-DLVL beams was investigated. A predictive finite element model of H-DLVL beams was created by the extended finite element method (XFEM) with cohesive zone model (CZM). The numerical models using solid-beam elements without fictitious cracks were verified and calibrated by experimental results. The influence of five variables, including lamina width, thickness, and quantity, dowel spacing along the grain, and dowel row (edge distance), on the flexural performance of H-DLVL beams was analyzed, and the flexural strength of H-DLVL beams was parameterized. The results showed that the failure mode of H-DLVL beams could be well predicted by XFEM without considering fictitious cracks combined with CZM, and the error range of simulated flexural strength of H-DLVL beams was within ±10 %. The flexural strength of H-DLVL beams was directly affected by lamina thickness and dowel spacing along the grain. The flexural strength of H-DLVL beams increased with the increase of those two variables. Lamina width and dowel row (edge distance) affected the flexural strength of H-DLVL beams indirectly by influencing the failure mode of H-DLVL beams. Based on this research, the recommended dowel spacing along the grain of H-DLVL beams was 6.25–12.5 times the wood dowel diameter, and the recommended edge distance of H-DLVL beams was 5–7 times.

Deformation level and specimen geometry in compression perpendicular to the grain of solid timber, GLT and CLT timber products

Compression Perpendicular to Grain (CPG) is a crucial aspect of timber design, particularly with the advent of engineering wood products like Cross Laminated Timber (CLT), often used in point-supported structures. After many years of discussion, the mechanics-based model by Van der Put has finally been included in the new Eurocode draft. This model offers a more systematic approach to design with a solid theoretical foundation for stress dispersion. However, there is still a need for improvement, especially in two areas: accounting for the capacity increment associated with increasing levels of deformation and determining the maximum effective height to be assumed in calculating the load spreading in deep timber elements. In this paper, the authors focus on these two areas of improvement for GLT, solid timber and CLT timber products. They analyse the data of two extensive experimental campaigns conducted at Norsk Treteknisk Institutt (Norwegian Institute of Wood Technology) and at the Norwegian University of Science and Technology (NTNU) on Glued Laminated Timber (GLT), Solid Timber (ST) and CLT. Additionally, they validated a parametric finite element (FE) model in Abaqus to assess the effect of the height of the timber element on stress distribution. A parametric approach developed in Abaqus aims to find the optimal height threshold to be assumed in the new code formulation.

Production and technical performance of scrimber composite manufactured from industrial low-value wood for structural applications

Development of scrimber composites and other engineered wood products from low-value wood and wood waste provides an effective opportunity to preserve natural resources, minimize waste, and innovate the production of higher-performance, environment-friendly construction materials. In this study, peeler cores, which are the center of poplar logs remaining after the peeling process in the veneer production, were utilized to develop scrimber composites. This study investigated the effects of different resins, including phenol-formaldehyde (PF) and urea formaldehyde (UF), as well as hydrothermal treatments at various temperatures (60 °C and 130 °C), on the physical and mechanical properties of the scrimber composites. Chemical changes in wood components and morphological changes in wood cell walls resulting from hydrothermal treatment were analyzed using Fourier transform infrared spectroscopy and scanning electron microscopy. To clarify how resin type and hydrothermal treatment affect structural performance, several physical and mechanical properties of scrimber composites, including thickness swelling, water absorption, internal bond strength, bending modulus of elasticity, and modulus of rupture, were measured. The test results revealed that hydrothermally treated wood scrims at 130 °C, when bonded with PF resin, produced scrimber composites with superior structural performance.

Image-based mesh generation for constructing a virtual representation of engineered wood product samples

The complex structure of timber has traditionally been difficult to model as it is a highly heterogeneous material. The density and material properties for structural species such as Pinus radiata (radiata pine) can vary greatly across the growth rings. Numerical simulation methods are becoming more prevalent as a method of predicting moisture migration, stress and strain distributions, and fungal/rot intrusion in engineered wood products (EWPs). All these applications require a computational mesh that captures the growth ring structure to facilitate an accurate assessment of the performance of EWPs. In this work, a low-cost image-based algorithm is developed for generating a virtual representation of a small cross laminated timber panel sample. Specifically, the proposed method results in a virtual description of an EWP sample comprised of a triangular prismatic mesh where the nodes are aligned on the growth rings of each individual timber component of the EWP, with specific wood material properties allocated to each mesh element. Each small component is treated individually and we assume there is no longitudinal variation in the density, pith location, and pith angle within the mesh structure. The initial step involves analysing an image of the end grain pattern of a single clear wood sample to identify the growth rings using a spectral clustering algorithm. Next, the centre of the tree (pith) is located through an iterative constrained least-squares algorithm to determine the pith angle. Image analysis of an anatomical image combined with the pith location allows for a constant density value to be assigned to each mesh element. The capability of this framework is then demonstrated by simulating the moisture migration and heat transfer throughout a CLT sample under atmospheric and saturating boundary conditions. Furthermore, the virtual representation provides the basis for simulating additional physical and biological phenomena, such as moisture-induced swelling, decay and fungal growth.

Proposed correction to the Gamma method for estimating the bending stiffness of CLT panels

Engineered wood products, such as Cross Laminated Timber (CLT), have been widely used in civil construction. Standard calculation methods, like the Gamma method commonly used in structural design, estimate the bending stiffness of elements. However, these methods are based on one-dimensional solids (bar elements), which can be limiting. This limitation may result in inaccurate estimates, especially when the panel's dimensions, measured in the median plane, significantly differ by an order of magnitude. In this research, a parametric study was carried out using the finite element method (three-dimensional approach), varying the panel's dimensions (width and length), the layers' thickness, and the number of layers (cross-section height), and adopting elastic properties considering either the wood's orthotropy or the rolling shear estimation (108 numerical simulations in all). Based on the parameterization, multiple variable regression models were used to establish a correction coefficient to be incorporated into the Gamma method to improve its accuracy in estimating bending stiffness. Therefore, the single adjusted equation (considering the wood's orthotropy) showed values closer to the numerical ones (MAPE = 0.95 %, RMSE = 2.96 × 1011 N⋅mm2, and CV = 1.60 %) than those obtained by the Gamma method (MAPE = 2.13 %, RMSE = 7.47 × 1011 N⋅mm2, and CV = 4.04 %).

Application of microscale methods to study the heat-induced delamination in engineered wood products bonded with one-component polyurethane adhesives

One-component polyurethanes (1-c-PUR) are commonly used adhesives for the manufacture of cross-laminated timber (CLT). Typically, these adhesives do not govern the mechanical response of CLT under normal service temperatures. However, when subjected to heating from a fire, failures may transition from within the timber to the bond line interphase zones. CLT bonded with 1-c-PUR has been shown to be prone to heat induced delamination (HID), which may compromise its structural performance at elevated temperatures. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic thermo-mechanical analysis (DTMA) were used to study the thermal and thermo-mechanical responses of engineered wood products and components (i.e. adhesives and timber) and their interphase (i.e. bond line). Two commercially available 1-c-PUR adhesive films from the same manufacturer, two timber species (Norway Spruce and Radiata Pine, as sawdust or as veneers), and four different veneer shear lap combinations, were studied. Shear lap specimens bonded with a conventional 1-c-PUR adhesive consistently experienced bond line mechanical failure in DTMA at about 220–240 °C. The same adhesive films tested via DSC and TGA softened at 240–260 °C. Conversely, a different 1-c-PUR adhesive, formulated specifically for enhanced performance at elevated temperature, displayed no detectable softening in DSC and TGA, and shear lap specimens in DTMA consistently failed within the timber; even at elevated temperatures. The presented thermo-mechanical methods allow identification of failure modes and temperatures, whilst the thermal microscale methods (i.e. TGA, DSC, DTMA) assist in understanding the various factors contributing to failures.

Theoretical and experimental studies on the bending properties of glued laminated timber manufactured with Chinese fir

China has been increasingly promoting the use of prefabricated timber structure buildings in recent years. However, unlike other countries, China lacks a diverse range of local tree species and engineered wood products suitable for load-bearing components in timber structures. This shortage poses a risk to the sustainable development of timber structures in China. This issue is addressed in this study, which focuses on the development and manufacture of glued laminated timber (GLT) using Chinese fir from plantation forests. The dynamic elastic modulus of 549 laminae was evaluated using the FAKOPP stress wave approach. A total of 28 laminae were randomly selected from Classes I, II, and III to assess the influence of stress grading on bending performance. This study included an analysis of failure modes, bending capacity, and the prediction model for bending stiffness of GLT with different layups and cross-sectional heights. The findings showed that the dynamic elastic modulus of the laminae followed a normal distribution. The bending strength and modulus of elasticity of finger-jointed laminae across different grades were 29.59 MPa to 37.05 MPa and 8.13 GPa to 10.94 GPa, respectively. The mechanical properties of both same-grade and mixed-grade composition GLT manufactured from Chinese fir met the TCT28 (MOR≥28 MPa, MOE≥8000 MPa) and TCYD24 (MOR ≥ 24 MPa, MOE ≥ 8000 MPa) garde requirements in GB/T26889, respectively. Failure modes in the GLT specimens typically began at the knots or finger joints of the bottom layer laminae. The cross-sectional height had no significant effect on the modulus of elasticity of GLT but exerted a significant effect on bending strength. The prediction model for bending stiffness, developed using the transformed section method, agreed with the experimental results. The outcome of this research provides a scientific and data-driven foundation for the application of Chinese fir in the field of structural materials.