Timber Boards Research Articles

Non-Destructive Assessment of the Dynamic Elasticity Modulus of Eucalyptus nitens Timber Boards.

Eucalyptus nitens is a fast-growing wood species with a relevant presence in countries like Australia and Chile. The sustainable construction goals have driven the search of structural applications for Eucalyptus nitens; however, this process has been complicated due to the defects usually presented in these timber boards. This study aims to evaluate the dynamic elasticity modulus (Exd) of Eucalyptus nitens timber boards through non-destructive vibration-based tests. Thirty-six timber boards with different levels of knots and cracks were instrumented and tested in a simply supported condition by measuring longitudinal and transverse vibrations. In the first stage, the Exd was calculated globally through simplified normative formulas. Then, in a second stage, the local variability of the Exd was estimated using operational modal analysis (OMA), finite element numerical simulations (FEM), and regional sensitivity analysis (RSA). The positive correlation found between the global static modulus of elasticity and Exd suggests that non-destructive techniques could be used as a reliable and fast alternative for the assessment of bending stiffness. Finally, the proposed method to estimate the local variability of Exdt based on the combination of OMA, FEM, and RSA techniques was useful to improve the structural selection process of timber boards for lightweight social housing floors.

Cyclic response of masonry piers retrofitted with timber frames and boards

The quasi-static in-plane cyclic response of two single-leaf calcium silicate unreinforced masonry piers was investigated to show the effectiveness of an innovative timber retrofit solution. The aim of the intervention is to increase the pier in-plane and out-of-plane strength and displacement capacity, thus reducing the seismic vulnerability of this typology of unreinforced masonry construction with a light, cost-effective, sustainable and reversible approach. The retrofit technique consists of a timber frame mechanically connected by means of steel fasteners to the masonry pier and building floors. Oriented strand timber boards are then nailed to the frame. In-plane quasi-static shear–compression cyclic tests were performed on two single-leaf calcium silicate brick piers with identical geometry and masonry mechanical properties: one was tested unstrengthened while the other was tested in the retrofitted configuration. The experimental results showed evident improvements in the lateral force–displacement response of the retrofitted specimen. More specifically, compared with the bare masonry pier, the retrofitted pier exhibited slightly higher stiffness, larger strength and significantly greater displacement capacity.

Rolling shear strength of timber boards

Problem Rolling shear strength and rolling shear modulus are important mechanical and elastic properties that have emerged recently and are needed when calculating multi-storey CLT buildings. Goal Rolling shear is a new task that requires determining the influencing factors on it’s magnitude as an indicator of the strength of the boards in the CLT panel. The failure mode of coniferous wood by rolling shear is observed at the boundary of the late and early wood annual rings, whereas for deciduous wood boards the failure mode is not clearly form but the strength values are higher and not dependent from the strength classes of the timber boards. Methodology Factors that influence the change in the strength by rolling shear are the geometrical parameters of the cross-section of solid timber boards, as well as technological features of the producing CLT panels, which are analyzed in this work on the basis of the technical approvals which contain tests results of panels strengths and stiffness for each plants which produce CLT. Rolling shear investigated and described in papers of many researchers over the past 10 years. Results The scientific novelty of this mechanical indicator for the national level is new and requires additional comparative research and implementation of practical recommendations by the consideration of rolling shear in the design of structures CLT panels buildings. Practical value The existing ukrainian standard for design timber structures DBN B.2.6-161: 2017 requires additions to the methods of calculating the CLT panels and strength velues and rigidity by the rolling shear.

Experimental investigation of mesoscale variability of clear spruce mechanical properties in the radial direction

The aim of this work is the investigation of mesoscale/local variability in mechanical properties of clear timber in the radial direction. Clear Norway spruce wood, Picea abies, was used for cutting specimens of different lengths with a small cross-sectional area of 4 × 4 mm2, in the radial direction of timber boards, and tested under tensile loading. In some boards, specimens were positioned regularly and, in some others, randomly, and local deformations in each specimen were measured during the tests. The results indicate a significant variability in the specimens’ elastic moduli and strengths. A correlation between the mesostructure of clear timber and mesoscale/local variability of the transverse elastic modulus in the specimens was observed. Specimens’ failures were classified and a reasonable correlation with the corresponding strength values was observed.

Evaluation of the RSIDTM-Saliva test to detect saliva in expirated bloodstains and development of an ‘in-scene’ protocol

ABSTRACT The differentiation between bloodstain patterns resulting from impact events and those from the expiration of blood can be crucial to crime scene reconstruction. Physical characteristics used to distinguish impact and expirated bloodstain patterns, are often unclear or absent, making interpretation of some bloodstain patterns difficult. Presumptive tests for salivary α-amylase (SAA) exist; however, these tests are generally unsuited for use at crime scenes or have not been tested on realistic expirated bloodstains. To address this, we assessed the RSIDTM-Saliva test for detecting SAA in expirated bloodstains and developed a modified protocol that can be used in-scene by forensic examiners. Phase 1 experiments, which involved volunteers creating simulated bloodstains by expirating volumes of their own blood onto painted timber boards, produced entirely positive results which demonstrated the test’s efficacy for realistic expirated bloodstains. Phase 2 development and evaluation of a modified in-scene protocol demonstrated that a reduced buffer volume and modified incubation could successfully detect SAA in expirated bloodstains. A significant inverse relationship was observed between the size of a bloodstain and the ‘time-to-positive’. These results support the modified RSIDTM-Saliva test protocol as a viable method to detect SAA in expirated bloodstains in a crime scene environment.

Inventory constrained design of a timber funicular structure

This research investigates the development of a digital form finding model that combines the generation of funicular geometry with a material inventory constraint. The model provides a flexible design tool that facilitates exploration of structural form whilst simultaneously satisfying two rationalizing criteria. It maintains an equilibrated structure derived from funicular geometry; and optimises the assignment of a unique inventory of timber members having natural dimensional variation. The combined goal for the design outcome is to achieve material efficiency through both structurally rational form and minimization of material waste. The material chosen for the inventory is utility-grade sawn timber, being lightweight but with high levels of naturally occurring structural variability. Sawn timber boards that are rejected for structural applications due to frequent structural defects (knots, checks, splits etc.) represent up to 50% of the sawn product produced by Australian sawmills, and are destined for under-valued non-structural use, chipping or burning. Yet these boards can readily yield usable short length structural members, once defects are removed. In doing so, the process creates a unique inventory of random short members. These short members are well suited to articulated structures, which, by employing an inverted funicular geometry, only incur axial stresses and can employ simple (non-moment resisting) timber connections. This form finding tool and a first prototype pavilion are proofs of concept for viable structural application of what is otherwise a significant source of waste in the timber industry.

Automatic detection of pith location along norway spruce timber boards on the basis of optical scanning

Knowledge of annual ring width and location of pith in relation to board cross-sections, and how these properties vary in the longitudinal direction of boards, is relevant for many purposes, such as assessment of shape mechanical properties and stability of sawn timber. Hence, the present research aims at developing a novel method and an algorithm, based on data obtained from optical surface scanning, by which the pith location along the length of sawn timber boards can be determined accurately and automatically. The first step of the method is to identify clear wood sections, free of defects along boards. Then time-frequency analysis, using the continuous wavelet transform, is applied to detect the surface annual ring width distribution of the four sides of the selected sections. Finally, the pith location is estimated by comparing annual ring width distributions on the different surfaces, and assuming that annual rings are concentric circles with the pith in the centre. The proposed algorithm was applied to a total sample of 104 Norway spruce boards. Results indicate that optical scanners and the suggested automatic method allow for accurate detection of annual ring width and location of pith along boards. For a sample of boards with the pith located within the cross-section, a mean error of 2.6 mm and 3.2 mm in the depth and thickness direction, respectively, was obtained. For a sample of boards of which 60% with pith located outside the cross-section, a mean discrepancy between automatically and manually determined pith locations of 3.9 mm and 5.8 mm in depth and thickness direction, respectively, was obtained.

Shear stiffness of inclined screws in timber–concrete composite beam with timber board interlayer

The timber board interlayer is applied as the formwork for the pouring of concrete slab in various practical applications of timber–concrete composite structures, with the rehabilitation of timber buildings, in particular. At present, there are few studies performed to study the shear stiffness of inclined screws in timber–concrete composite beams with timber board interlayer. In this article, eight groups of shear tests were carried out to study the shear stiffness of inclined screws in timber–concrete composite beams with timber board interlayer. The key parameters included the embedment depth of the screw connector into timber, screw diameter, the thickness of concrete slab, and concrete strength. As indicated by the test results, the shear stiffness of the inclined screws was improved as the embedment depth of screw into timber and screw diameter increased. When the embedded depth of screw into concrete remained unchanged, the thickness of concrete slab and concrete strength exhibited no significant impact on the shear stiffness of inclined crossing screws. On the basis of the theory of a beam on a two-dimensional elastic foundation, the calculation method for predicting the shear stiffness of inclined screw in timber–concrete composite beams with interlayer was proposed. The comparisons demonstrated that the shear stiffness of inclined screw can be well predicted using the calculation method.

COMPOSITE BEHAVIOUR OF COLD‐FORMED STEEL ‐ TIMBER FLOORS

AbstractThis article investigates, experimentally, the structural performance of lightweight cold‐formed steel (CFS) ‐ timber board composite flooring systems. Fifteen full‐scale bending tests and twelve companion pushout connection tests were performed. The effect of connection detail (comprising self‐drilling screws with or without a structural adhesive) on structural performance is examined. The results of this research demonstrate that the use of a polyurethane adhesive, in conjunction with screws, leads to a significant increase in connection slip modulus and a higher degree of composite action in the floors, resulting in up to 40% increase in flexural stiffness, when compared to joists designed individually. The experimental results are then compared to predictions from relevant existing analytical models.

Behaviour of Timber-Concrete Joints in Hybrid Members Subjected to Flexure

Possibility to develop rigid timber-concrete joint for hybrid timber-concrete specimens was stated. Behaviour of timber-concrete rigid and compliant joints were evaluated numerically and by experiment for the members subjected to flexure. Small scale hybrid timber-concrete specimens with the length, width and thickness equal to 400, 95 and 43 mm were investigated for case of three points bending. The small-scale hybrid timber-concrete specimens consists from the layers of cement base finishing mass Sacret BAM and timber boards of strength class C24 with thicknesses equal to 25 and 18 mm, correspondingly. The rigid timber-concrete joint was provided by the pieces of crushed granite, which were strengthened on the surface of the timber boards by epoxy glue Sica Dur 330. Dimensions of the crushed granite pieces changes within the limits from 2 to 25 mm. The compliant timber-concrete joint was provided by the screws with diameter and length equal to 4 and 40 mm, correspondingly. The screws were placed under the angles equal to 45 and 90 degrees relatively to the direction of fibres of the timber layers. Load-carrying capacity and maximum vertical displacements were gotten for groups of small-scale hybrid timber-concrete specimens with rigid and compliant timber-concrete joints. It was shown that providing of rigid timber-concrete joint enables to decrease 1.86 - 3.50 times the maximum vertical displacements of hybrid timber-concrete specimens. Load-carrying capacity of the specimens grows by 16.5 – 50.0% at the same moment.

Cost optimisation of glued laminated timber roof structures using genetic algorithms

Roof structures comprising of heavy timber trusses and purlins made of glued laminated timber, as well as dowels and metal plates used as mechanical joints, are widely employed, among others, in agro-industrial settings that require large open areas. This paper presents the economic optimisation of such roof structures through the use genetic algorithm models. Two phases of optimisation were carried out: firstly, in two dimensions for a single truss and, then, an entire roof structure in three dimensions. Both models followed a discrete approach, i.e. the optimisation of the cross-section was limited by the characteristics of the commercially-available glulam timber boards, an aspect not yet included in the literature. Therefore, the models allowed the influence of the laminate thickness in the optimisation to be estimated, but also allow comparisons with the continuous cross-section variation found in the literature. Furthermore, the optimisation took into account a range of configurations of trusses, number of joints and separation between trusses and purlins. The genetic algorithms were shown as an efficient optimisation tool for roof glulam structures as a function of the laminate thickness. Among the results obtained, the most cost-effective solutions were those comprised of the fewer number of joints in the trusses and the lowest laminate thickness of those studied. Moreover, the optimal separations between trusses and purlins were also determined. Finally, a simplified method of optimum pre-dimensioning was also proposed.

An advanced virtual grading method for wood based on surface information of knots

Strength grading of timber boards is an important step before boards can be used as lamellas in glued laminated timber. Grading is generally done visually or by machine, whereby machine grading is the faster and more accurate process. Machine grading gives the best strength prediction when dynamic modulus of elasticity (MoEdyn) is measured and some kind of knot assessment algorithm is included as well. As access to the actual density for the measurement of MoEdyn may be impossible in some conditions, this grading method may face some problems in strength prediction. As the strength of a board is related to its natural defects and the ability of the stress waves to propagate around these defects, a virtual method for more accurate strength predictions is developed based on the knot information on the surface. Full 3D reconstruction of the boards, based on knot information on the surfaces of these boards, is an important step in this study. Simulations were run for 450 boards of spruce, Douglas fir, beech, ash and maple, covering a large quality range. Abaqus and Python were used for the numerical simulations. From the numerical simulations, three different stress concentration factors were calculated in the vicinity of the defects. Additionally, a virtual longitudinal stress wave propagation was modeled for the determination of the dynamic modulus of elasticity. The FEM results were used to predict the tensile strength. By means of a regression analysis, the correlation with actual visual and machine readings was validated. An improvement in the strength prediction was observed based on the virtual method, when compared to currently available grading machines. It shows the potential of numerical methods for strength prediction of wood based on visual knot information.

Behaviour of locally post-tensioned nail laminated high mass floor panels under serviceability loads

ABSTRACTThis paper investigated the behaviour of locally post-tensioned nail laminated high mass floor panels. Each panel was assembled using butt jointed timber boards. Post tensioning was applied using bracing straps. A total of six panels were tested under four-point bending. The dynamic behaviour of the floor panels was also investigated Results showed that post-tensioning reduced the deflection by almost 50% under the serviceability loading condition. However, the damping ratio was reduced under dynamic tests, though it remained within acceptable limits.

Flexural performance of cross-laminated timber constructed from fibre-managed plantation eucalyptus

This study was performed to evaluate the flexural performance of three-ply cross-laminated timber (CLT) floor panels made of unthinned and unpruned plantation Eucalyptus. The impact of the stress-grade of the timber boards on the modulus of elasticity (MOE) and modulus of rupture (MOR) of the panels was determined. The results indicated that the actual MOE of the timber boards from both species could not be appropriately estimated by visual stress-grading. The results revealed that the average MOE and MOR of the panels were significantly affected by the stress-grade of the boards in the top and bottom layers of the panels. The CLT panels made with high-grade boards showed respectively 24% and 21% higher MOE values than comparable panels made with low-grade boards for E. nitens and E. globulus. The failure modes were bending failure on the tensile side and rolling shear for the panels made of low-grade and high-grade boards, respectively. On average, the CLT panels made of E. globulus showed 17.7% higher MOE and 32.5% higher MOR values than comparable panels made of E. nitens.

A NUMERICAL STUDY OF THE EFFECT OF GREEN-STATE MOISTURE CONTENT ON STRESS DEVELOPMENT IN TIMBER BOARDS DURING DRYING S Florisson, S Ormarsson, J Vessby

Timber boards manufactured with a traditional sawing pattern often contain both heartwood and sapwood. The difference in moisture content between heartwood (30-60%) and sapwood regions (120-200%) result in a radial moisture variation that can cause internal constraints during drying. However, the green state moisture content is seldom considered when evaluating kiln drying schedules. The developed numerical model is able to simulate stress development in timber boards, which are dried from green state to equilibrium moisture content. The model studied the effect of initial moisture content on stress development in timber boards during drying. The model operates on continuum level and consists of a coupled transient non-linear orthotropic moisture flow analysis, while a stress analysis considers elastic, hygroscopic and mechano-sorptive strain behaviour with use of the finite element method. The simulations were performed on four different timber board configurations, each defined by a unique pith location. The study shows that the green state moisture content does not necessarily lead to significant constraints, but has a positive effect on the maximum tensile stress found in tangential direction at the exchange surfaces in the beginning of the drying process. In this stage, stress development is mainly governed by shrinkage close to the surface, which is partly prevented due to regions still above the fibre saturation point. The initial MC can also influence the time when the maximum stress occurs, but not necessarily the location.

Strength prediction of timber boards using 3D FE-analysis

Timber boards are numerically reconstructed in the full 3D space based on knot information on the wood surface. The 3D model is then transformed into a full 3D-FEM model and successively used for tensile strength prediction. By knowing the exact locations of the knots, as the main strength governing parameters in timber boards, simulations are run for a large quality range of wood laminations. This includes low-medium quality Douglas fir and medium-high quality spruce boards. ABAQUS and PYTHON are used for the numerical simulations. An automatic link is programmed to extract data of the database and to create the 3D geometrical model. From the numerical simulations, three mathematical methods are presented to calculate the stress concentration factors (SCFs) around the 3D heterogeneous defects in anisotropic wooden boards. Additionally, the explicit dynamic analysis are run to obtain the dynamic modulus of elasticity (MoEdyn). To reduce the dependency of the numerical predictions on the real density of the boards, the average density of each sample is used for the simulations. Each board is tested in tension physically and is used for the validation of the model. The FEM results are used in a regression analysis to analyze the correlation with the visual measurements and to predict the tensile strength. Based on the results of a multiple regression analysis, two SCFs and MoEdyn are sufficient to accurately predict the strength of spruce and Douglas fir boards. The results of the current study show that an improvement in the strength prediction of wood is possible in comparison with current machine grading systems based on dynamic MoE and knot parameters.

Characterization and Structural Performance in Bending of CLT Panels Made from Small-Diameter Logs of Loblolly/Slash Pine.

The main objective of this work was to study the structural viability of using small-diameter logs of Uruguayan Loblolly/Slash pine, mainly from thinning operations, to design cross-laminated timber (CLT) panels. A visual grade named “CTH” (coniferous thinning) was proposed, and 45 specimens of sawn timber boards were tested, resulting in 51% lower bending strength than that of the minimum strength class C14. Subsequently, 20 CLT panels were manufactured and experimentally tested, the results showed that the bending strength of the CLT panels was 43% above that of the individual layers. Additionally, the structural performance of the CLT panels for use in floors was calculated, and the thickness-span relationship depending on strength class and imposed load are presented. Results showed than the use of CTH timber to design CLT floors implies a volume (m3/m2) 17% higher than that using C24 timber.

Defectos en madera de eucalipto asociados a daños por heladas en Entre Ríos, Argentina

En un rodal de Eucalyptus grandis afectado por heladas se estudió la asociación entre daños por heladas y defectos en la madera. Cuatro meses después de las heladas se clasificaron 40 árboles de 3 años en 3 clases de daño por heladas: sin daño aparente, ápice seco, toda la copa dañada; se les midió altura y diámetro normal (DAP) y dos años después se midieron nuevamente y se apearon 19 individuos de las 3 clases. En las dos primeras trozas se estimó el módulo de elasticidad dinámico (MOE) y en las tablas se registró presencia de médula, pudrición, grietas y kino. Los datos se analizaron con modelos mixtos, prueba LSD de Fisher, análisis de correspondencia múltiple y modelos lineales generalizados mixtos. En la primera medición los árboles sin daño aparente presentaban altura y DAP significativamente mayores a los demás. Dos años después de la primera medición los árboles que habían presentado toda la copa dañada mostraron valores de DAP significativamente menores. El MOE de las segundas trozas resultó significativamente mayor en árboles sin daño aparente comparados con los de toda la copa dañada. Solo se observó pudrición en árboles con daño visible, pero sin diferencias significativas en la proporción de tablas con pudrición en las dos clases. La asociación entre grietas y daño por heladas no fue significativa. El daño por heladas según la escala usada se asocia con pudrición en tablas y con el módulo de elasticidad de las trozas.

Validation of Orthotropic Parameters of Timber by Means of Elastic Layer Theory

The known solution of isotropic elastic layer was modified for orthotropic elastic material behavior in this contribution. The solution was original derived for calculation of footing settlement. However it should be useful for estimation of orthotropic material parameters. Timber is classical orthotropic material. Timber board which is placed on the rigid basement it could be considered as the elastic layer. From the known load displacement curve we can, vice versa, estimate the material parameters. The present solution should be able to control loading by rigid strip footing acting perpendicular to the plane of orthotropy. The contribution summarize the first steps of the proposed back analysis.

Slope of grain measurement: a tool to improve machine strength grading by detecting top ruptures

Severe local fiber deviation in timber boards can lead to reduced strength values. As grading machines do traditionally not detect these deviations, such boards are typically assigned to higher strength values than they actually possess. Based on statistics, these cases are taken into account in machine grading. Slope of grain can be measured on the surface by laser diffraction. The aim of this study is to estimate the reducing effect of local slope of grain on tensile strength, which is caused by top ruptures and the impact on the grading results of machine strength grading. This is investigated in full-scale tensile tests. In total, 192 test specimens of Norway spruce (Picea abies) with more or less pronounced local slope of grain were selected, measured and strength-tested to show the influence of local slope of grain on tensile strength. The utilized timber was sawn from relatively small diameter logs. The grain angle was determined on all four longitudinal sides of the boards with the help of a dense matrix. A model is presented for estimation of the grain deviation over the cross section of the sawn timber. These values are converted into a strength-reducing factor taking into account the ratio of tensile strength parallel and perpendicular to the grain. The introduced strength prediction algorithm is tested for the investigated sample. Improvement of the reliability and economy of timber grading using grain angle as an additional parameter will be possible. Furthermore, it is shown that different strength-reducing features such as top ruptures in sawn timber can be located on the specimens, and the strength-reducing effect can be estimated. Local slope of grain around knots is not part of this study.