Glulam Research Articles

In-situ characteristic elastic properties of bond-lines in laminated engineered wood products using microscopic digital image correlation

Adhesively laminated engineered wood products (EWPs), such as glue-laminated timber (GLT) and cross-laminated timber (CLT), have gained global popularity due to the increasing development of tall wood buildings. The mechanical performance of a bond-lines is crucial for the structural behavior of EWPs. In this study, a novel method was developed for evaluating in-situ elastic properties of a bond-line in adhesively laminated solid wood products. This method deployed the microscopic digital image correlation (DIC) technique to capture the strain distribution along the bond-line under axial (0°) and off-axis (45°) tensile loading. Three types of adhesives, namely polyurethane (PUR), emulsion polymer isocyanate (EPI), and phenol–resorcinol–formaldehyde (PRF), were used to make specimens. The modulus of elasticity (E) and modulus of shear (G) of a bond-line were accordingly calculated based on the strain along a bond-line and load applied on a specimen. For verification purpose, finite element (FEA) models on CLT and GLT beams were, considering the elastic properties of bond-lines and disregarding the elastic properties, developed to evaluate the effects of the elastic properties of a bond-line on the stress distribution. It was found that the proposed method could be used to accurately determine the in-situ characteristic elastic properties of bond-lines in EWPs. The elastic properties of a bond-line exhibited a large variability, but did not appear to have a significant impact on the overall stress distribution in a specimen. The E and G of bond-lines might be neglected in the structural analysis of large-sized laminated wood products such as GLT and CLT.

Study on vibration performance and comfort of glulam beam and deck floor

Study on vibration performance and comfort of glulam beam and deck floor

Experimental investigation of the bending creep behavior of glulam beam reinforced with near surface mounted steel bars

ABSTRACT In this study, the pull-up tests of glued-in steel bar were conducted, and the results showed that ensuring the anchorage length of the steel bar can obtain desired mechanical behavior of the glued-in steel bar. The creep tests were performed on two unreinforced glulam beams with different stress ratios and four glulam beams reinforced with near surface mounted steel bar. After 65-day test periods, the test results found that mounting the steel bar at both compression and tension sides of the glulam beam can decrease the creep coefficients by at least 0.32 when compared to the unreinforced glulam beam. By employing the power function, Burger and proposed modified model, it was found that the proposed modified model had the best goodness of fit, followed by thepower function model. Through the analysis of the creep coefficients predicted by the modified model, it was found that values of the creep coefficients for the reinforced glulam beams were almost half of those for the unreinforced glulam beams. Thus, it was recommended that the glulam beam reinforced with smaller diameter steel bar mounted at compression or tension side can be usedfor the long-term design of the glulam beam in practice.

Enhancement of the contact behavior of a quasi-isotropic carbon fiber/epoxy matrix laminate with an elastic body by modifying the fiber-matrix interphase using graphene nanoplatelets

This study analyzed the effect of incorporating graphene nanoplatelets in the fiber-matrix interphase on the behavior of a multiscale composite laminate based on carbon fibers and epoxy resin subjected to contact loads. The selected loading mode was the contact between an elastic surface and a cylinder. The multiscale composite material used was a quasi-isotropic laminate with graphene nanoplatelets (GnPs) added at the fiber-matrix interface. The specimens were prepared with 0.0%, 0.1%, and 0.25% by-weight GnPs. Laminate beams were used according to the ASTM D7264 standard, and contact was studied in two configurations, applying the load at the edge of the laminate and in the other, in the plane of the test pieces. The normal strains in the contact region were determined experimentally using the interferometric Moiré technique. These results were compared with estimations using the Hertz contact theory and the finite element method (FEM). The normal strains in the contact area of specimens with fibers modified with 0.1% GnPs were lower than those with 0.25% or fibers without surface modification. Excellent agreement between the experimental results along lines in the contact zone with those estimated with the FEM. The normal strains in a direction perpendicular to the applied load obtained by the Hertz theory for the maximum deformation were slightly higher than those obtained by FEM. Except for those calculated for the normal strain in εy for the load in the direction of the thickness, although the distribution was very similar to those obtained by FEM as well as the experimental one.

A New Moment-Resisting Glulam Beam-End Connection Utilizing Mechanically Fastened Steel Rods—An Experimental Study

A new moment-resisting mass timber connection was designed based on the principles of force equilibrium in applied mechanics. The connection configuration utilizing two mechanically fastened threaded steel rods embedded into the end of a glulam beam section was experimentally investigated in this study. A gradually increasing transverse load was applied to the free end of a cantilevered beam, causing a bending moment on the beam-end connection until failure. Four different connection configurations were examined, each replicated twice to verify results. The beam connection parameters investigated were rod anchorage length (200 and 250 mm) and square washer size (38.1 and 50.8 mm). Test results show that increasing the washer size increased the connection bending strength by increments more significantly than those due to increasing the rod anchorage length. However, the connection configurations with the smaller-size washer, which failed mainly due to wood crushing under the washer, had higher ductility ratios than those with the larger-size washer, which failed due to steel rod yielding. In a real-life scenario, a structural element such as a glulam beam is usually loaded to approximately 50% to 70% of its design capacity, considering a reasonable margin of safety. The study estimates a maximum possible bending moment utilization factor for the strongest connection configuration that ranged between 34% and 48% compared to the maximum moment resistance of a supported glulam beam spanning an average length of 4.0 m to 6.0 m (a common span length in framed timber buildings) and has a cross-section size same as the one utilized in this study. This utilization factor is quite large for a timber connection, and thus, confirms a considerable moment-resisting capability of the new configuration developed in this study.

Experimental study and theoretical analysis of fire resistance properties of prestressed glued laminated timber beams

The addition of prestressing not only improves the force resistance of glulam beams, but also provides a potential solution to improve their fire resistance. An in-depth study of the fire behavior of prestressed glulam beams (PGBs) under fire and the force behavior after fire is essential for their fire resistance design and evaluation. In this paper, fire tests and post-fire four-point bending experiments were conducted on the PGBs aiming to investigate the thermal response of the PGBs as well as their force resistance after fire. The results showed that fire significantly affected the mechanical properties of the PGBs, not only reducing the prestressing force during the fire, but also decreasing the residual load carrying capacity after the fire. After 60 min of standard fire exposure, the prestress and load capacity of the PGBs decreased by 10 % and 33.33 %, respectively. Increasing either prestress or reinforcement ratio can effectively improve the resistance performance of the PGBs after fire. In the same fire action time, if the prestress was increased by 59.46 % or the reinforcement ratio was increased by 0.53 %, the residual ultimate load capacity of the PGBs was increased by 17.14 % and 22.19 %, respectively. The study also indicates that fully utilizing the synergistic effect of prestressing and reinforcement ratio enhancement can significantly improve the overall performance of the PGBs. In addition, a theoretical calculation model is proposed to accurately predict the residual flexural capacity of the PGBs after fire, which provides a theoretical support for the fire-resistant design of the PGBs before fire and the assessment of residual load capacity after fire.

Experimental study of failure of glulam-concrete composite beams

AbstractThis paper is dedicated to the memory of Dr. Miklós Iványi, who instilled in the authors an appreciation for experimental investigations, which are foundational to understanding material and structural behavior. Timber-concrete composite structures are increasingly adopted for new buildings due to their favorable sustainability parameters and the increased availability of cross laminated timber. For larger spans, however, solid timber floors lead to higher timber volumes and the use of glulam beams may become necessary for a more efficient use of wood. This paper presents laboratory tests of glulam-concrete composite beams and is the first in a series of two papers on investigating the associated failure mechanisms. Three full-scale glulam-concrete beam specimens were studied. The glulam and concrete are monolithically interconnected using a continuous layer of adhesive. Shear reinforcement was added to the glulam beams to allow for failure mode control. Static load tests to failure were conducted along with acoustic emission monitoring to track the progression of the failure. The results indicate that the shear reinforcement of the glulam layer affects the load capacity of the composite beam through shifting the failure from a shear to a tension failure mode. Similar glulam-concrete beams can enable larger span applications for buildings and bridges while maintaining an attractive sustainability performance.

Analytical model for prestressed glulam beams reinforced with unbonded steel bars

Glulam beams reinforced with bonded steel bars are a common form. The study describes theoretical models of unbonded reinforced and prestressed reinforced glulam beams for assessing the reinforcement ratio and prestress level range, and for predicting the effect of unbonded steel bars on the flexural capacity of the beam. Considering the stress changes of beam cracking and cross-sectional stress, the minimum and maximum reinforcement ratios were determined. On this basis, the influence of the service load on the beam in the actual engineering was explored, and the force equilibrium equation was established to derive a reasonable prestress range related to the reinforcement ratio. Combined with the glulam constitutive model, and analyzed the strain distribution of unbonded steel bars was to establish the flexural capacity prediction model. The accuracy of the model was verified by the relative error between the prediction and test values ranging from-11.78% to 8.84%.

Experimental study of hybrid pine-birch glued-laminated timber beams assisted by digital image correlation technique

Experimental study of hybrid pine-birch glued-laminated timber beams assisted by digital image correlation technique

Effect of Layers Number on The Bending Properties of Chestnut Glulam Beams

In recent years, advances in adhesive and lamination technologies have offered significant opportunities in the production of high-quality and valuable products from low-quality and non-durable cheap wood raw materials. Lamination generally refers to a multilayer material production method. The main goal of this production process is to develop and improve many properties of the created composite product, such as durability and stability. Laminated timber, called glulam, is a layered composite material formed by preparing timber fibers parallel to each other and gluing them together with the help of glue. In this study, the bending properties of solid, 3-layer and 5-layer glulam beams produced from chestnut tree species were investigated experimentally and numerically. The modulus of elasticity (MOE) of 5-layer glulam beams is 13.39% higher than 3-layer beams and 48.31% higher than solid beams. The modulus of rupture (MOR) value of the 5-layer beam is 24.21% higher than the 3-layer beam and 65.28% higher than the solid beam. There is a maximum difference of 2% between the experimental and numerical analysis results. When the results are compared, it is seen that the results are close to each other.

Comparative investigation on beam-to-beam connection with different types of connecting plates

The spliced glued laminated timber (glulam) beams have extensive applications in large-span timber structures since the length of the long solid wood beams is limited by transportation and construction. This paper investigated the flexural performance of glulam beam-to-beam connections with connecting plates and self-trapping screws. The influence of connecting plate types (steel plate, bamboo scrimber, and plybamboo plate) on the flexural performance of the spliced beams was studied. A total of 12 beams were designed, including the intact beam group (3 specimens) and the spliced beam group (9 specimens). The failure modes, ultimate bearing capacity, stiffness, moment-rotation curves, and carbon emissions of spliced beams with different connecting plates were studied. The test results showed that the failure mode of the spliced beams mainly included bending failure of glulam and fracture of the connecting plates. The average bearing capacity of the spliced beams with bamboo scrimber plates and those with steel plates could reach the intact beams. The average stiffness of the spliced beams with bamboo scrimber plates was higher than that of the splice beams with steel plates, reaching 97.6% of the intact beams. The average bearing capacity and stiffness of the splice beams with plybamboo plate reached 80.9% and 92.7% of the intact beams, respectively. A theoretical model of the spliced beams with bamboo scrimber plates was proposed and verified by tests data. Comparisons of the analytical and the test results reveal that the model can predict the moment capacity of the spliced beams with bamboo scrimber plates corresponding specific failure mode in this test.

A study of the accuracy of industrial robots and laser-tracking for timber machining across the workspace

ABSTRACT The aim of the present study was to investigate the accuracy of an industrial robot when milling glued-laminated timber along a vertical work plane while maximising the advantageous size of the workspace. The authors discovered a research gap in the machining accuracy within the workspace of an industrial robot. Hence, the examination comprises 50 distinct positions allocated in a grid, each with 3 machined specimens resulting in a total of 150 samples. The workpiece positions were referenced using laser-tracking technology to adjust the robot machining code to the actual workpiece position, while simultaneously assessing the machining accuracy using laser scans of the samples. As a result, accuracy maps are presented indicating the nominal-actual deviation including referencing errors and workpiece dimensional deviations (absolute accuracy) and the robot-only nominal-actual deviation (relative accuracy), subsequently proving that both comply with the EN 14080 standard. Furthermore, a calculation of the centre of accuracy defines the point of highest relative accuracy. The objective was achieved and advocated for a more pronounced utilisation of the workspace when machining timber with industrial robots. Applying these insights to the machining of large complex parts, multi-workpiece stacks and mobile robot platforms can enhance the possibilities and efficiency within timber construction.

Fiber-steered acoustic black hole beam with low cut-on frequency and high stiffness

This study proposes an acoustic black hole (ABH) beam with varying carbon fiber orientation and thickness for a low cut-on frequency and high stiffness. The proposed fiber-steered ABH beam contains a laminate with a varying fiber orientation as a junction between a tapered 90° laminate and uniform 0° laminate. The anisotropic viscoelastic properties of the carbon fiber-reinforced plastic were identified using dynamic mechanical analysis tests and a micromechanics model for fiber composites. An analytical model was developed to derive the solutions for the displacement field, cut-on frequency, and reflection coefficient. The analytical solutions demonstrated that varying the fiber orientation contributes to the decrease in the cut-on frequency and the reduction of the reflection coefficient while maintaining the stiffness of the host structure. Finite element method analyses were performed to investigate the frequency response of the fiber-steered ABH beam. The fiber-steered ABH beam exhibited lower resonance peaks than the uniform 0° laminate beam. The higher loss tangent of the 90° laminate compared to that of the 0° laminate improved the damping performance without an additional viscoelastic material layer. The frequency response calculated using the analytical solution agreed well with the numerical analysis results.

Reinforcement for earthquake-damaged glued-laminated timber knee-braced frames with self-tapping screws and CFRP fabric

Glued-laminated Timber Post and Beam Structure (GTPBS) is favored in timber engineering, primarily due to its commendable seismic resistance. Nonetheless, under severe earthquakes, these structures are susceptible to damage. This study aims to understand the impact of diverse reinforcement techniques on the lateral resistance of earthquake-damaged GTPBS. For this purpose, two full-scale frames were reinforced using self-tapping screws and Carbon Fiber Reinforced Polymer (CFRP) fabric before being subjected to horizontal low-cycle reversed loading tests. An in-depth comparison was made considering failure modes, hysteresis curves, and other pertinent parameters of the specimens both before and after reinforcement. Evidently, the employment of both self-tapping screws and CFRP fabric reinforcements curtailed the initiation and progression of joints cracks, averting premature structural failures. In addition, the better ductility of knee brace makes it more suitable for reinforcing earthquake-damaged GTPBS. These reinforcement techniques managed to recover over 90% of the bearing capacity of earthquake-damaged GTPBS, with a notable boost in their stiffness and ductility. The study culminates with an energy analysis that delves into the transformation and relative contributions of hysteresis energy and elastic strain energy during loading. From this analysis, it emerged that reinforcements using self-tapping screws and CFRP fabric not only ensure structural robustness but also maintain consistent energy dissipation.

Bending Behavior of Hybrid Timber-Steel Beams.

Driven by climate change and the need for a more sustainable construction sector, policy is increasingly demanding and promoting timber hybrid construction methods. In the German state of Baden-Württemberg, every new public building has to be of timber or timber hybrid construction (Holzbauoffensive BW). The objective of multi-story buildings with large floor spans can only be achieved in a resource-efficient way by hybrid constructions combining timber and steel components. A research project recently completed at the Karlsruhe Institute of Technology was aimed at the development and systematic investigation of hybrid bending beams in which an advantageous combination of the materials steel and timber is used. For this purpose, steel profiles are integrated into timber cross-sections in a shear-resistant manner by adhesive bonding. As part of the experimental, numerical and analytical investigations, different cross-sections of steel and timber, as well as different construction materials, were considered (GL24h, LVL48p, LVL80p, S355 and S420). The results of large-scale four-point bending tests illustrate the potential of this new hybrid construction method. Depending on the geometry and material combinations tested, the bending stiffness could be increased by up to 250%, and the load-carrying capacity by up to 120%, compared to a glulam beam with identical dimensions.

ASYMMETRIC FLEXURAL BEHAVIOR OF GLULAM BEAMS BASED ON BAMBOO-INSPIRED FUNCTIONALLY GRADED STRUCTURE FOR HIGH BENDING LOAD APPLICATIONS

ABSTRACT Natural materials are being further processed into functionally engineered products to reduce their natural variability and enhance their performance for use in construction, given their noteworthy recyclability, availability and sustainability traits. To date, the mechanical strengths of natural and engineered wood products are limited by their inherent micromechanical characteristics which are outclassed by homogeneous materials like steel and concrete. This study proposes a less process-intensive technique to improve the strength of engineered wood products by considering glulam based on a bio-inspired functionally graded structure. The finite element method was considered to investigate the effects of the functionally graded arrangement on the asymmetric flexural deformation and on the underlying fracture mechanisms in glulam beams. The numerical results showed that the functionally graded arrangements across the cross-section led to an improvement in the bending strength and consequently enhanced the resistance to transverse crack propagation. In the functionally graded glulam beam, the stiffer layers at the bottom were found to promote the onset for longitudinal crack initiation. Moreover, transverse cracks tended to propagate sideways in an orthogonal direction in the beam layers with a high longitudinal to transverse stiffness ratio whereby the tangential normal stress was a maximum. The improvement in performance, which resulted from a shift of the neutral axis and redistribution of stress within the glulam beams, was attributed to the degree of graded arrangement across their cross-section besides the orthotropic characteristics of their individual layers. Key findings of this study could be useful to further develop high-strength engineered wood products based on bio-inspired solutions to replace conventional materials in the construction industry for improved sustainability.

A finite element simulation approach for glued-laminated timber beams using continuum-damage model and sequentially linear analysis

Glued-laminated timber (GLT) is an efficient and renewable material with potential to enhance sustainability in construction, but its potential has been partly hindered by relatively large uncertainty related to its strength. Previous research indicate that by linking information from the grading process to the GLT fabrication more reliable GLT beams could be made. To this end, this paper represents a finite element based modelling approach combining a continuum damage model with sequentially linear analysis that is suitable for simulation of the bending stiffness and strength of GLT beams. The model has been implemented in Matlab and can be easily integrated into different parametric simulation workflows. Based on validation against 36 experimentally tested GLT beams, the model can predict bending stiffness with high accuracy and provides reasonably accurate predictions for bending strength. The model is also capable of producing qualitatively realistic fracture patterns of GLT beams. The mesh-size study suggests that the best agreement for bending strength with test data is obtained with a sparse mesh, which is discussed in detail. The model is considered suitable for follow-up studies involving the optimization of GLT beam layups.

Drawing a blank – design modelling composite timber elements

The shift towards bio-economies of architectural fabrication necessitates particular consideration of how characterizing aspects of bio-materials such as heterogeneity and anisotropy impact the designed performance of architectural elements. These aspects must be integrated into the modelling and representation of architecture and must be instrumentalised for digital design and fabrication processes. The use of timber in construction is challenging due to its complex material behaviours, and therefore robust methods for predicting and modelling these are crucial for exploiting the timber resource more effectively. In light of this, we focus on developing a holistic and integrated digital modelling approach for glue-laminated timber construction elements that connects the digital design model to the specific material resource and incorporates its material complexity into design simulation workflows. We question the role of the lamella in the glulam blank and trace its agency through a series of four disparate projects, from an initially silent and generic constituent of the blank to a key, operative actor in the design of performance-graded timber products through the added specificity of material composition and a liberation of its form. The first project develops a modelling approach that connects material specification and lamella sizing to free-form timber element geometries. It uses principles of industrial glulam production and knowledge of the anisotropic nature of timber to speculate on new forms of glulam blanks that could arise from a deeper engagement with the glue-lamination process. The second project looks further back in the timber value chain at the processing of the specific forest resource into tailored building elements, attaching a material specificity to the lamella. The third project expands the modelling and prototyping of non-standard glulam blanks into considerations of timber waste streams and aesthetics. The final project aims to further speciate the lamella by tailoring its form as well as its material composition to respond to simulated performance demands. Through these projects we outline the development of a novel digital framework that begins as a modelling approach for free-form glulam beams and grows to accommodate the mapping and allocation of specific, heterogeneous input material. As the digital framework matures, increasingly detailed and interlinked digital simulations of mechanical performance are integrated.

Bending Behaviour and Failure Modes of Non-Glue-Laminated Timber Beams Composed of Wooden Dowels and Self-Tapping Screws

The purpose of this research is to compare the bending behaviour of non-glue-laminated timber beams and glulams by full-scale four-point bending tests. The focus is on the non-glue beams laminated by different materials or techniques and then to determine their bending stiffness and failure modes. The laminating efficiency of various materials or techniques is underlined. The manufacturing process concerning non-glue-laminated timber beams has to be determined. As structural elements with large dimensions, such components require adaptable laminating and producing techniques. While the beams composed of wooden dowels refer to the dowel-laminated timber (DLT), those made of self-tapping screws (STSs) can be simply related to nail-laminated timber (NLT) products. Then, a full-scale four-point bending test was carried out to appraise 26 laminated beams, including non-glue- and glue-laminated timber. The results of the test demonstrated that the material, the spacing and the angle of the transversal fasteners significantly influence bending behaviour. The bending stiffness of the beams laminated by STSs was about 7.86% higher than the value of the beams with wooden dowels, although the tendency of each pair of beams did not remain convergent. Reducing the interval of the fasteners can considerably increase the bending stiffness of the beams. Fasteners inserted at 45 degrees, or in a so-called V-type pattern, contribute to improving bending stiffness, and both wooden dowels and STSs reveal the same tendency. At this angle, STSs demonstrate better laminating efficiency than wooden dowels. The STS beams’ bending stiffness was about 48.6% of that determined for glulams. On the contrary, in beams with 135-degree fasteners, or, namely, an A-type pattern, inserted fasteners possessed lower bending stiffness than in those with 90-degree fasteners. In addition to the considerable bending stiffness, the STS beams revealed a stable response as far as their load-deflection curves were concerned. A comparison of experimental and theoretical results contributes to verifying the feasibility as well as the weakness of two analytic methods. The predicting capacity of the associated equations needs to be improved, particularly for the withdrawal resistance and connecting effect of inclined STSs.

Steel-Reinforced Columns Made of European Beech Glued-Laminated Timber

Steel-Reinforced Columns Made of European Beech Glued-Laminated Timber