Glulam Research Articles

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

Properties of hybrid glued-laminated timber manufactured from peeler cores

ABSTRACT The aim of the present study was to determine some basic physical and mechanical properties of a hybrid glued-laminated timber manufactured from peeler cores (GLPC) as by-products of plywood manufacturing, ensuring more complete and efficient utilisation of wood raw materials in high value-added applications. The GLPCs were manufactured from beech and poplar wood at different ratios by using several combinations of lamellae with trapezoidal cross-sections. The highest density ρmax of 572 kg.m−3 (ρmean = 544 ± 12.9 kg.m−3) was determined for the beams manufactured at beech:poplar ratio of 1:1. The modulus of rupture (MOR) and modulus of elasticity (MOE) were 71 ± 9.4 N.mm−2 and 12,809 ± 1211.7 N.mm−2, respectively. The highest shear strength were obtained for the beams manufactured by gluing beech to beech: f v , g , k ( 60 ) = 17 ± 3.8 N.mm−2. The greatest values when testing the compressive strength and tensile strength of the GLPC were found for combination beech 50%/ poplar 50%: f c , g , k ( 90 ) = 60 ± 8.6 N.mm−2 and f t ( 0 ) , g , k = 42 ± 8.0 N.mm−2. All types of beams produced in laboratory conditions met the minimum requirements of the GL 32c and GL 32 h classes.

Predicted and Experimental Bending Behaviour of Glulam Bonded by RPF Adhesive.

In this study, alder, spruce, and beech woods were used for homogeneous symmetric, inhomogeneous symmetric (combined) and inhomogeneous non-symmetric glued laminated timber (glulam) beams glued with resorcinol phenol formaldehyde (RPF) adhesive. The aim of this paper is to determine and compare the modulus of elasticity of glulam beams using three methods, i.e., analytical calculation, numerical model (FEM) and experimental testing. As an additional characteristic, the bending strength (MOR) of the beams was determined during experimental testing. Analytical calculation was used to calculate the modulus of elasticity (MOE) of glued laminated timber based on the knowledge of the modulus of elasticity of solid wood and to estimate the location of the neutral axis during bending. According to calculations, for symmetrical combinations, the deviation from the real neutral axis does not exceed 5%. In the case of the modulus of elasticity, the deviation is an average of 4.1% from that of the actual measured beams. The numerical model includes finite element modelling, where the deflection of the modelled beams can be calculated with a deviation of up to 10%. The last method was experimental testing of glued beams using four-point bending, in which, among homogeneous beams, beech glulam beams achieved the highest MOE and MOR, while alder glulam beams achieved the lowest. The combination of wood species resulted in an increase in both MOE and MOR compared to homogeneous spruce and alder beams.

Behaviour of glued-laminated timber beams under impact loading

Short duration loads, such as impact loading, have the potential to generate catastrophic effects on infrastructure and loss of life. Although design provisions for engineered wood products are included in Canada’s blast design standard, CSA S850, how these structural materials respond to blast and impact loads across a wide range of high strain rates has not been well documented. An experimental program was carried out using a newly established Drop Weight Impact Testing Facility to investigate the flexural behaviour of glued-laminated timber beams subjected to impact loading. High strain rates were generated, whereby the dynamic specimens were found to differ quantitatively and qualitatively from their quasi-static counterparts. Dynamic increase factors of 1.13 and 1.20 were observed on the peak resistance and initial stiffness, respectively. A single-degree-of-freedom model was developed and validated against the experimental test results, where it was found to accurately predict the displacement–time histories of the specimens until failure.

Timber-concrete composites (TCC) floors subjected to hogging moment

In this paper, the structural behaviour of timber precast concrete composite (TCC) beam-to-column subassemblies subjected to hogging bending moments is investigated. Full-scale testing and analytical modelling are undertaken on timber precast concrete composite joints and beams. The composite actions were transferred via coach (lag) screw shear connectors embedded in the small grout pockets. The laboratory tests were designed to determine the influence of the size and type of timber beams (i.e., laminated veneer lumber (LVL) or glued laminated timber (GLT)), size of screw shear connectors and amount of reinforcement (in the slabs) on the structural behaviour (i.e., load-displacement, stiffness, capacity, and ductility) of the TCC beam-to-column connections. The hogging moment capacity and stiffness of the TCC floors with nominal slab thickness of 80 mm and reinforcing ratio (in the range of 0.9–1.8%) were up to 24% and 17% higher than that of the bare timber beam, respectively. The size of coach screw shear connectors (in the range of 8–16 mm) had less than 13% effect on the capacity and stiffness. An analytical model for calculating the peak load and stiffness of the TCC beams under hogging bending moment is developed. The model is shown to perform well when compared to the collected test data.

Compression properties of glued laminated timber and tensile properties of gluelam lamellas from oil palm wood

ABSTRACT When oil palm lumber is considered for load-bearing products such as glued laminated timber (GLT), defined strength and stiffness values are required. In this investigation, combined GLT from oil palm wood is tested in compression parallel and perpendicular and glulam lamellas in tension parallel to the vascular bundles. Strength and Young´s modulus in compression and tension parallel increase with the density by power law relationship. In contrast to dicotyle­dons, the strength in construction size exceeds that of small, defect-free test specimens (compression strength perpendicular), are in the same range (tensile and bending strength parallel) or only a little below (compression strength parallel). The specimen size does not influence the strength. The ratio of fc,0 : fm : ft,0 is 1.2 : 0.8 … 1.7 … 2.6 : 1 and fc,0 : fc,90 = 2.7 … 13.0 … 32.6 : 1 for ρ = 200 … 400 … 600 kg/m³; the ratio of Ec,0 : Em : Et,0 is 1.2 : 1.3 : 1 for ρ = 400 kg/m³. Ashby´s performance indices for minimum weight design rise with the density; the strength-density performance indices are comparable or only slightly lower than that for structural size softwood, whereas the modulus-density performance indices are much lower. The challenge in use of oil palm wood for load-bearing construction products is the low stiffness.