Glulam Research Articles

Influence of the moisture content on the fracture energy and tensile strength of hardwood spotted gum sawn timber and adhesive bonds (gluelines)

This study aims to measure the fracture properties, including crack initiation and propagation, of Australia’s native forest grown spotted gum ([SPG], Corymbia citriodora) sawn timber and associated adhesive bonds at different moisture content levels. The collected data were used as input values to develop a numerical model to understand the delamination of SPG glulam beams when exposed to a wetting and drying process. Thus, Mode I and Mode II fracture energies for crack propagation along radial and glueline directions were experimentally investigated under various moisture content levels (8%, 12% and 16%). Single-end notched beams and compact shear specimens were used to capture the Mode I and Mode II fracture energies, respectively. For crack initiation, the tensile strength perpendicular to the grain and the shear strength (taken as the maximum stress from the Mode II fracture tests) were also measured. In total, 200 experimental tests were performed. One-way analysis of variance statistical analyses showed that the fracture energies and shear strengths were independent of the range of moisture content levels investigated. In addition, the collected data were compared with the limited published fracture properties of other hardwood species.

Experimental and theoretical investigation of the structural behavior of reinforced glulam wooden members by NSM steel bars and shear reinforcement CFRP sheet

Abstract Reinforcing the wooden structural members is considered as a challenging matter to overcome the drawbacks of using wood in the construction field. The current investigation, therefore, presents an attempt to evaluate the effectiveness of utilizing steel bars as reinforcements in glulam timber beams using the near-surface-mounted (NSM) technique in conjunction with carbon fiber-reinforced polymer (CFRP) sheet wraps. A series of flexural testing was carried out until failure for both reinforced and unreinforced glulam members in a simple support system. Eleven specimens were examined in two groups to compare them with the control beam. Five reinforced glulam (RG) beams of the first group were reinforced with different schemes at tension and compression zones using the same bar size. The other five specimens of the second group were reinforced with shear reinforcement using fully wrapped strips made of CFRP sheet in addition to the same flexural reinforcement schemes as the first group. Each glulam beam has a span of 1.35 m and a rectangular section sized 85 mm × 175 mm. Based on experimental outcomes, theoretic modeling was provided to estimate the ultimate load capacity and bending rigidity of reinforcing glulam members. Though several theoretical predictions of flexural capacity were overstated when compared to experimental predictions, these disparities were frequently about 10%, confirming that the proposed theoretical model was accurate, and the mean of ultimate loading capacity and deflection between experimental and theoretical results were 1.01 and 1.09, respectively. Experimental results presented show that the RG beams performed much better than the unreinforced reference beams in terms of structural behavior, with improvements in ultimate load capacity ranging from 16 to 49%. On the other hand, the shear reinforcement for RG members slightly improved flexural performance, and the ultimate load capacity increased by 2–7%. Therefore, it was concluded that the NSM techniques using ordinary steel bars were effective ways in strengthening the glulam members in terms of flexural stiffness with increasing ultimate load capacity.

Research on mechanical property of glued timber truss connected by steel plates and bolts

In order to deeply understand the mechanical performance of glued-laminated timber trusses connected by steel-plates and bolts, two groups of truss specimens were designed and fabricated by changing the connection forms of the nodes, while maintaining the height and span of the trusses unchanged. Each group of truss specimens was subjected to the mid-span load. At the same time, finite element numerical analysis was conducted on the tested trusses. Based on the agreement between the experimental and numerical simulation results, the influence of the parameters of thickness-to-diameter ratio and height-to-span ratio on the mechanical performance of these trusses was explored. The research results show that both types of node connections in the glued-laminated timber trusses have good bearing capacity. The main failure modes are the splitting of the diagonal web members at the mid-span node and the crushing failure of the bolt holes. The HJ-C type truss, which has the upper and lower chord members connected, exhibits better ductility, greater stiffness, and better structural synergy in load-bearing capacity. As the thickness-to-diameter ratio increases, the form of the bolts at the truss failure gradually changes from being straight to yielding. The optimal thickness-to-diameter ratio is 8.3. As the height-to-span ratio decreases, the initial stiffness and ultimate load-bearing capacity of the truss show a decreasing trend. The truss exhibits better mechanical performance when the height-to-span ratio is 1/4.

Glue laminated timber beams in pinus: analytical and experimental study of flexural stiffness

In the current global scenario, where demand for sustainable development is paramount, the prestige associated with the applicability of wood as a primary structural element on a scale never before achieved characterizes it as the building material of the 21st century. This is due to its structural, economic, energetic, and environmental principles, and abundant availability in nature. Among the new wood-based products, significant attention is directed toward the Glued Laminated Timber (Glulam) structural system, owing to its enhanced strength characteristics. As this construction system gains momentum in the Brazilian Civil Engineering sector, the technological classification of mechanical properties becomes a critical point for the effectiveness of its implementation, both in terms of quality control and compatibility with the resistance parameters mandated by prevailing regulations. Thus, the objective of this present study is to investigate, through statistical analyses, the characterization of the mechanical parameter of the Elastic Modulus of eight Glulam beams, fabricated using Pinus conifer wood and monocomponent polyurethane adhesive material. This investigation is conducted via non-destructive experimental flexural and static tests, considering a predefined maximum displacement as the stopping criterion, along with the analytical method of transformed section, as proposed by the Brazilian standard ABNT NBR 7190:2011. The results of experimental characterization in structural dimensions and analytical predictions exhibit a high statistical agreement, with a strong correlation of approximately 79.0%.

Effects of Bolt Number and Pattern on the Failure Time of Minimally Fire-Protected Glulam Beam Connections Reinforced with Self-tapping Screws

Effects of Bolt Number and Pattern on the Failure Time of Minimally Fire-Protected Glulam Beam Connections Reinforced with Self-tapping Screws

A new concept for column-to-column connections for multi-storey timber buildings—Numerical and experimental investigations

A new jointing concept for the vertical load transfer between glued laminated timber (GLT) columns in multi-storey timber buildings has been developed. The basic components of the connection are two stepped, pyramid-shaped inserts made from block-glued laminated veneer lumber (LVL), which are bonded oppositely into corresponding cavities of the jointed GLTs. The load transfer between the mating columns relies on an intermediate LVL pin, fitting into pyramid-type cavities. Beech LVL was chosen for both, insert and pin, due to its 2.2 times higher characteristic compressive strength as compared to the employed high-strength softwood GLT (GL32h). The form fit of the stepped components which are bonded together relies on high precision robotic milling and a gap-filling two-component polyurethane adhesive. Manufacturing and mechanical performance of the scalable connection was investigated with full-sized specimens, achieving up to 90% of the characteristic GLT compressive capacity of 1040kN for a cross-section of 180mm×180mm. A parametric model based on the finite element method (FEM) showed a good agreement with empiric strain distributions and provided a stress-spread angle of 35° for the concentrated vertical load for an analytical design approach. The location and magnitude of tensile stresses perpendicular to the grain causing splitting failure was identified by FEM. Reinforcement by self-tapping screws proved a significant load-capacity enhancement. The mean experimental axial compressive load capacity exceeded the analytical prediction by 19%. First investigations on the rotational stiffness delivered a value of 240kNm/rad. The column utilization due to additional directly supported floor slabs was assessed exclusively by FEM. The calculation results predict a significant reduction of the tensile stresses perpendicular to the grain to be verified experimentally.

ANALYSIS OF FINGER-JOINTS IN GLASS FIBER-REINFORCED POLYMER (GFRP) COMPOSITE GLUED LAMINATED TIMBER BEAMS

The objective of this paper was to evaluate the effect of finger-joint reinforcement on thebending strength and stiffness of glulam beams made from high-density Eucalyptus spp. glued with resorcinol-formaldehyde adhesive.Six glulam beams were tested: three reinforced with glass fiber-reinforced polymer(GFRP) and three unreinforced for comparison. The GFRP was placed between the last two laminatesand at the bottom edge of theglulam only in the finger-joint position. The stiffness and strength of glulam beams were evaluated using static bending tests, which showed that the use of GFRP reinforcement resulted in a gain of more than 100% in average ultimate bending moment and about 10% in average bending stiffness. Tocalculate the theoretical bending stiffness and normal stresses, a theoretical analysis of beam bending was performed using the transformed section method, which showed agreement with the experimental results.

Manufacturing Study on Different Glue Spread and Press Pressure for Glued Laminated Timber Made from Laran

Amidst challenges such as dwindling timber log supply from natural forests, concerns about timber quality, and rising timber costs, the timber industry has increasingly turned to engineered lumber solutions, including glued laminated timber (glulam) crafted from fast-growing species. However, the performance of glulam derived from plantation trees, notably swift-growing varieties like Laran, remains an area warranting exploration. This study addresses critical aspects of glulam production, encompassing adhesive selection, spread rate, and press pressure, which collectively influence material performance. The objectives of this research encompass an assessment of the bonding integrity of glulam originating from Laran plantation species and an evaluation of the optimal adhesive spread rate and press pressure for Laran-derived glulam. Various adhesive spread rates (200 g/m2, 250 g/m2, 350 g/m2 and 400 g/m2) and press pressures (0.7, 1.0 and 1.4 MPa), utilizing Phenol-Resorcinol Formaldehyde (PRF) adhesives, were systematically investigated in alignment with the guidelines stipulated in MS 758: 2020. Bonding integrity was evaluated via block shear and cyclic delamination tests. The study reveals that these parameters indeed exert a tangible influence on the bonding efficacy of PRF adhesive with Laran species. Remarkably, an optimal adhesive spread rate of 399.78 g/m2 and press pressure of 1.18 MPa emerged as pivotal thresholds for superior bonding outcomes. Notably, the significance of adeptly designed glulam beams within wooden structural frameworks is underscored, particularly in light of the multifaceted imperatives of sustainability, economics, and environmental conscientiousness.

Bonding Performance of Melamine–Urea–Formaldehyde and Polyurethane Adhesives for Laminated Hybrid Beams and Their Selected Mechanical Properties

Beech (Fagus Sylvatica L.) is a prevalent tree species in Slovenia and is suitable for manufacturing glulam beams. However, beech wood has certain limitations that can potentially be mitigated by combining it with Norway spruce (Picea abies (L.) Karst.) wood to create hybrid beams. This study aimed to determine the bonding performance of commonly used melamine–urea–formaldehyde and polyurethane adhesives for these hybrid beams. Moreover, how varying the proportion of beech wood in a hybrid beam affects its mechanical properties was examined. Shear and delamination tests (method B) were conducted, and EN 14080:2013 requirements were met in all cases. The four-point bending tests of the beams showed that hybrid beams containing 20% of beech wood in the cross-sectional height on each side of the neutral axis exhibited a similar modulus of elasticity values as pure beech beams, but their strength was not equally improved. Hybrid beams with 11% of beech wood did not show any improvement in bending stiffness or strength compared to pure spruce beams. It was noted that the presence of beech wood in a hybrid beam can influence its failure mode. Furthermore, analytical calculations showed that a symmetrical lay-up is preferable to an asymmetrical one to increase the effective modulus of elasticity.

Comparison of mechanical properties according to the structural materials of lumber, GLT, CLT, and Ply-lam CLT

The mechanical properties of materials such as lumber (L), glued laminated timber (GLT), cross-laminated timber (CLT), and Ply-lam CLT (P), which are laminated in cross layers, were compared. As a result, the modulus of elasticity (MOE) was 9.7 to 10.3 GPa, showing no significant difference between the materials. Modulus of rupture (MOR) of L and GLT showed higher strength than that of CLT and P. MOR of CLT and P was at the same level, and there was no difference in strength according to the plywood and lumber arranged alternately. Alternatively, there was a difference in the coefficient of variation of the materials, and CLT and P was 20.2% and 11.8%, respectively; therefore, uniform properties can be secured when using plywood. The compression strength showed the highest compression strength in the order of GLT, L, P, and CLT. P was failure by buckling+delamination, but other materials showed failure by only buckling. The adhesion of P passed the glulam standard (7.0 MPa), and the delamination ratio was very low at 0.41%. It can be used together with CLT. This study is expected to be used as basic data for establishing quality standards.

Numerical Analysis of Flexural Performances of Composite Steel-Timber Beams under Fire Conditions

Recently, a novel type of composite structure, composite steel-timber (CST) structure, has attracted much attention by combining steel and timber in an effective way to form composite structural components, which unitises the advantages of high strength and excellent ductility of steel and decent sustainability and fire resistance of timber. However, the existing research is lacking, especially in structural fire design and analysis. In this study, based on the sequentially coupled method, the commercial finite element software ABAQUS was used to numerically simulate the dynamic performances in the temperature field and the flexural behaviours in the displacement field for a typical CST beam with a steel element embedded within the Glulam and connected by adhesives and bolts under standard fire for two hours. In the numerical simulations, the temperature distributions within the CST beam were explored, and the flexural performances of the beam in the displacement field were examined. Through the comparative analysis, the temperature distributions in the embedded steel beam and the surrounding Glulam beam under one-hour standard fire verified the advantages of this type of CST beam in structural fire design. Specifically, under a 2-hour standard fire, the surrounding Glulam could still protect the embedded steel beam from sustaining too high temperatures, so as to retain most of its material properties and help maintain the bearing capacity of the whole structure and improve the refractory limit. Parametric studies on the fire resistance of the CST beam were also conducted by adjusting the bolt spacing and the protection thickness of the Glulam. The obtained results indicated that reducing the bolt spacing and the thickness of the Glulam protection layer would have an adverse effect on the temperature distributions in the embedded steel element to a large extent, and would eventually lead to its rapid heating and strength loss and the final failure of the whole CST structure.

Experimental Study of Glued Laminated Timber (Glulam) from Jackfruit Wood and Coconut Wood for Timber Beams of Level Houses in East Nusa Tenggara

Wood is a construction material that is familiar to the wider community. Wood can be used in construction. The purpose of this study was to determine the specifications of the physical properties, mechanical properties, tensile strength and flexural strength of laminated wood (glulam), in jackfruit and coconut wood beams originating from the East Nusa Tenggara region in multi-storey house buildings. The tests carried out included testing the water content, testing the tensile strength and bending strength, testing the tensile strength and bending strength on glulam beams using epoxy glue adhesives. The results of this study showed that jackfruit wood and coconut wood aged 15 years and 20 years had an average moisture content of 15 years, namely 15% and 26%, the average specific gravity was 0.54 (tons/m3) and 0.46 (tons/m3). Meanwhile, the average water content for 20 years is 15% and 32%, the average specific gravity is 0.58 (Ton/m3) and 0.45 (Ton/m3). The tensile strength of intact and glulam wood of jackfruit and coconut wood was obtained from laboratory results on SNI 7973-2013 calculations, the average tensile strength of intact jackfruit and coconut wood was 84.40 MPa and 80.73 MPa. The flexural strength of intact beams and glulam of jackfruit and coconut wood aged 15 years was obtained from laboratory results on SNI 7973-2013 calculations of the flexural strength of intact beams for 15 years, the average being 71.81 MPa and 26.07 MPa. At 15 years of age, the flexural strength of glulam beams was the highest variation 1 and variation 2 (Jackfruit, Coconut, Jackfruit) mean 76.00 MPa and 41.85 MPa. The flexural strength of intact beams and gulam of jackfruit and coconut wood aged 20 years was obtained by laboratory results on SNI 7973-2013 calculations of flexural strength of intact beams, which were 80.27 MPa and 29.73 MPa respectively. At the age of 20 years, the highest flexural strength of glulam beams were variations 1 and 2 (Coconut, Jackfruit, Coconut) with an average of 80.40 MPa and 48.76 Mpa.

Evaluation of the shear size effect in glued laminated timber using a stochastic FE model calibrated on 17000 glue-line tests

Glue-line tests provide the shear resistance and failure mode of samples extracted from laminated timber products. Several papers questioned the practical use of such tests affirming the lack of correlation between the capacity of the beam and the outcomes of glue-line tests. However, no studies provide a probabilistic framework for interpreting glue-line tests. This paper presents and discusses the largest database of glue-line tests ever published, consisting of approximately 17000 tests on glued laminated timber (GLT) beams, carried out at the Treteknisk, the Norwegian Institute of Wood Technology (Norway). This database has been used to develop in Abaqus a stochastic FE model to predict the shear capacity of glued laminated timber beams (GLT) using advanced modelling concepts, including discrete cracking and plasticity. The authors examine the dependence of the shear capacity on the beam size to assess the shear size effect in GLT components. The methodology is based on Montecarlo simulations. The mechanical properties of the elementary volumes composing the beam are assigned using a random field model calibrated on the glue-line tests.

The Time-Dependent Behavior of Glulam Beams from European Hornbeam

This paper presents the results of an experimental investigation of glued laminated timber (glulam) beams made from European hornbeam (Carpinus betulus L.) under constant loading for three months. Glulam beams were experimentally tested as a part of the last phase of the research project conducted by Drvene konstrukcije Ltd. and the Faculty of Civil Engineering, Architecture and Geodesy, Split. Beams were loaded in four-point bending tests with the applied load levels of 20% and 30% of the maximum force obtained from previously performed short-term tests. The experiments were carried out under minor environmental changes at the specialized laboratory unit at the Faculty of Civil Engineering, Architecture, and Geodesy, Split. The objective of this study is to present the research results of bending creep tests for hardwood species not included in the European Assessment Document. The experimentally obtained deflection-time curves were fitted with the power law equation used for the prediction of creep behavior. The results indicate that the power law fits well with experimental data. A comparison with requirements from Eurocode 5 is given.

Physical and mechanical properties of Albizia procera glulam beam

This research was done to evaluate the feasibility of using Albizia procera for manufacturing glulam beams. The physical and mechanical properties of the A. procera glulam beam were evaluated, and these properties were compared to those of the solid A. procera solid timber. The A. procera glulam beam’s physical and mechanical properties were all superior to solid A. procera timber. In comparison to A. procera solid timber, A. procera glulam’s density, water absorption (WA), linear expansion (LE), and thickness swelling (TS) all improved by 11.1, 48.4, 44.6, and 37.0%, respectively. Again, compared to A. procera solid timber, the modulus of rupture (MOR) and modulus of elasticity (MOE) of the A. procera glulam beam increased by 27.6 and 29.2%, respectively. Additionally, the ASTM specifications were met by the A. procera glulam beam. As a result, based on the properties, it is possible to make A. procera glulam beams as structural timber products.

Development of lignin-reinforced polyurethane adhesive for glued laminated timber

Glued-laminated timber (Glulam), a structural engineered wood product, is mostly manufactured using structural adhesives including one-component polyurethane (PUR). Nevertheless, the concerns associated with PUR such as unsatisfactory gap-filling properties and lower resistance to delamination create opportunities for newer adhesives with enhanced bonding performance in outdoor environments. In this study, the use of fractionated lignin as a modifier in a polyurethane-based adhesive system was explored. Herein, the effect of lignin content (1, 2, and 3%) on the block shear strength (BSS), wood failure percentage (WFP), and delamination were evaluated. The results indicated that all the lignin-reinforced PUR specimens showed better adhesion performance compared to the controls (without lignin). Markedly, the lignin-PUR adhesive formulation containing 1% lignin addition exhibited superior adhesion properties than those with 2% and 3% lignin content. The statistical analyses also revealed that the lignin content influenced the BSS and WFP of the glulam specimens. Moreover, the lignin-modified PUR specimens showed increased delamination resistance and met the requirements for delamination stipulated in the ASTM D2559 standard, regardless of the lignin content. The lowest percent delamination (0.07%) was obtained from specimens bonded with 1% lignin. The presented data suggest that specimens bonded with 1% of lignin provided better bonding strength compared to other lignin-filled specimens. Thus, this study demonstrated the technical feasibility of fabricating glulam with enhanced adhesion performance using lignin-modified PUR adhesive.

THE POTENTIAL OF PRODUCING HIGH ADDED VALUE STRUCTURAL TIMBER FROM LAMELLAE WASTE. CLASSIFICATION AND VISUAL GRADING

This study is the continuation of the first part (Horváth et al. 2023), in which density, bending strength and modulus of elasticity of 100 oak lamellae generated as small-sized production waste were investigated. In this part of the study series, the classification of our sample set is carried out according to the EN 338. A visual pre-grading is presented, to remove the worst specimens and achieve a better final result and a standardized visual grading is also shown. Our results are compared with literature values of clear specimens as well. Amount of 80% of the specimens were found to be suitable for further structural use. The total sample set is classified in strength class D35 (average density 712.6±72.5 kg/m3; average MoRadj 65.4±16.2 MPa; average MoEadj 13.4±3.1 GPa), while the visually pre-graded part with better average test results is classified in strength class D45. Industrial wood residues contain a sufficiently high proportion of elements for further processing, so that after sorting it can be used as raw material for glued-laminated load-bearing timber.

Bending behavior and bond analysis on adhesively bonded glulam-concrete panels fabricated with wet bonding technique

In this paper, we report on the effect of adhesive type on the bending behavior of adhesively bonded glulam-concrete composite panels. Steel-reinforced and unreinforced concrete were bonded to glued-laminated timber (GL-24 h) panels with polyurethane (PUR) and epoxy adhesives using the wet bonding technique. The PUR and epoxy adhesives (both were two-component adhesives) were selected to represent brittle and ductile adhesive behaviors. Four-point bending load was applied to glulam-concrete composite panels to investigate their bending behavior. The bending behavior measured includes bending load vs. mid-span deflection, strain distribution at the mid-span of the panel, and strain distribution between the loading point and its adjacent support. These were determined by linear variable differential transformers (LVDTs), strain gauges, and digital image correlation (DIC) technique. The experimental results showed that polyurethane-bonded glulam-unreinforced concrete panels showed similar load vs. mid-span deflection curves to epoxy-bonded glulam-unreinforced concrete panels and epoxy-bonded glulam-reinforced concrete panels. The shear stress, shear deformation, and peel strain analyses at the adhesive bond line showed that debonding at the glulam-concrete interface was more likely to occur for panels bonded with the ductile polyurethane.

Stochastic FE analysis of stress concentrations in curved glulam beams due to the uncertainty of material direction

When curved glulam beams are subjected to bending, tension perpendicular to grain is introduced. In this work, Monte-Carlo analysis is conducted to study the influence of the annual-ring orientation of individual board on stress concentration in the radial direction. A virtual cutting program is developed which simulates the sawing processes of boards and yields a database of sawn boards, each with a characterized material direction with respect to the pith location. Lamellas are randomly selected from the database to construct curved glulam beams in FE models for Monte-Carlo simulation. Parameters including lumber diameter distribution, taper function, orthotropic elastic properties are considered for four common wood genera in Europe: spruce, pine, larch, and beech.Statistical analysis shows that when the annual-ring effect is considered, the average radial stress in the middle height area of the glulam beams can reach up 1.56 times (even higher on the middle width and height area) compared to the common practice, where wood is usually simplified as transverse isotropic material. Such stress concentration, which can trigger early damage of the structure, indicates an underestimation of stress perpendicular to grain in common practice. Moreover, parameter studies show that the stress redistribution depends not only on the mechanical properties of wood species but also on the width of the board layer.

Modulus of Elasticity and Flexural Behavior of Glulam Beams Reinforced with Steel Mesh in Different Mesh Openings.

In this study, the modulus of elasticity and flexural strength properties of laminated wood elements reinforced with steel mesh with different mesh openings were determined. In accordance with the purpose of the study, three- and five-layer laminated elements were produced from scotch pine (Pinus sylvestris L.) wood material, which is widely used in the wood construction industry in Türkiye. The 50, 70, and 90 mesh steel used as the support layer was placed between each lamella and pressed with polyvinylacetate (PVAc-D4) and polyurethane (PUR-D4) adhesives. Afterward, the prepared test samples were kept for 3 weeks at 20 °C temperature and 65 ± 5% relative humidity for 3 weeks. The flexural strength and modulus of elasticity in flexural of the prepared test samples were determined according to the TS EN 408: 2010+A1 standard by the Zwick universal tester. Multiple analysis of variance (MANOVA) was carried out using MSTAT-C 1.2 software to determine the effect of the modulus of elasticity and flexural strength on the obtained flexural properties, the mesh opening of the support layer, and the adhesive type. When the differences within or between groups were significant with a margin of error of 0.05, achievement rankings were made using the Duncan test on the basis of the least significant difference. According to the results of the research, the highest bending strength (120.3 N/mm2) was obtained in three-layer samples reinforced with 50 mesh steel wire and bonded with Pol-D4 glue, and the highest modulus of elasticity (8969.3 N/mm2) was obtained in three-layer samples reinforced with 50 mesh steel wire and bonded with Pol-D4 glue. As a result, the reinforcement of the laminated wood material with steel wire had an increasing effect on the strength. Accordingly, the use of 50 mesh steel wire can be recommended to increase mechanical properties.