Glued Laminated Timber Beams Research Articles

Modeling approach to estimate the bending strength and failure mechanisms of glued laminated timber beams

The numerical simulation of four-point bending tests on glued laminated timber (GLT) beams requires an adequate description of the material behavior and of relevant failure mechanisms. The wooden lamellas, building up the GLT element, include knots, as a result of the natural tree growth process, which significantly affect the mechanical behavior. The variability of the morphology and arrangement of these knots lead to a large fluctuation, especially of strength properties, along the wooden lamellas. This leads to complex and, in general, quite brittle structural failure mechanisms of the GLT element. Such failure mechanisms can numerically be described with discrete cracks, using the framework of the extended finite element method (XFEM) for cracks without predefined positions or cohesive surfaces for cracks with predefined positions. In this work, a modeling approach to reliably estimate the bending strength and failure mechanisms of GLT beams subjected to four-point bending tests is proposed. Herein, the approach is validated by simulating replications of experimentally tested GLT beams of two beam sizes and strength classes, where each knot group is considered as a section with reduced individual stiffness and strength in exactly the same position as in the real beam. The results show that the application of quasi-brittle material failure may still result in a brittle global failure of GLT beams. The present study exemplarily shows how valuable insight into progressive failure processes can be gained by allowing the formation of continuous crack patterns. Moreover, a refined consideration of the knot geometries with such sophisticated realizations of discrete cracks may be able to simulate the actual failure mechanisms even more precisely.

Fire performance of hybrid mass timber beam-end connections with perpendicular-to-wood grain reinforcement

PurposeThe fire resistance of timber structures is heavily dependent on the fire behaviour of the connections between its structural elements. The experimental study presented in this paper aimed to investigate the fire performance of glued-laminated timber beam connections reinforced perpendicular-to-wood grain with self-tapping screws (STS).Design/methodology/approachTwo full-size fire experiments were conducted on glulam beam-end connections loaded in flexure bending. Two connection configurations, each utilizing four steel bolts arranged in two different patterns, were reinforced perpendicular to wood grain using STS. The bolt heads and nuts and the steel plate top and bottom edges were fire protected using wood plugs and strips, respectively. Each connection configuration was loaded to 100% of the ultimate design load of the weakest unreinforced configuration. The test assemblies were exposed to elevated temperatures that followed the CAN/ULC-S101 standard fire time–temperature curve.FindingsThe experimental results show that the influence of the STS was significant as it prevented the occurrence of wood splitting and row shear-out and as a result, increased the fire resistance time of the connections. The time to failure of both connection configurations exceeded the minimum fire resistance rating specified as 45 min for combustible construction in applicable building codes.Originality/valueThe experimental data show the effectiveness of a simple fire protection system (i.e. wood plugs and strips) along with the utilization of STS on the rotational behaviour, charring rate, fire resistance time and failure mode of the proposed hybrid mass timber beam-end connection configurations.

The flexural strength of glue laminated timber beams based on deflection and strain rate with four point bending loading system

The development of utilization of low quality wood as construction material is needed to reduce the exploitation of natural forests. However, low quality wood species have disadvantages in terms of mechanical properties. The mechanical properties of Sengon wood are relatively low, so it does not qualify as a structural element. Therefore, the system glulam can be applied to overcome this problem. The system glulam can produce relatively light structural elements with adequate performance. This system has been extensively developed, even at the stage of applying external reinforcement, to improve the performance of structural laminated beams. On that basis, this study aims to determine the flexural strength of laminated beams of Sengon wood as a low quality wood species. In order to achieve this goal, the laminated beam was tested using method four point bending test method. Tests were carried out on long span laminated beams (L = 2750 mm) to observe flexural strength. There are five (5) laminated blocks tested, namely (BLS-1, BLS-2, BLS-3, BLS-4 and BLS-5). Each group has dimensions of 55 mm in width and 155 mm in height. Each specimen consists of six layers of wood boards with a density Falcata 0.3 g / cm3. The thickness of each layer was 26 mm and bonded with resin urea formaldehyde cold setting. Double-sided adhesive laying of 350 gr / m2 at a compressive force of 2 MPa. The analysis result shows that the load-deflection relationship between BS-L consists of linear and nonlinear phases. The load performance characteristics of the two types of laminated beams are expressed as the ratio of the proportional limit load to the maximum load. The ratio value is expressed in the form P eBL-s = 0.7P max BL-S andM eBL-s = 0.7M max BL-S. This form is similar to previous studies with a Pe to Pmax ratio of 0.80.9. In this case, the average flexural strength of the laminated beam is 17 MPa with a maximum strain of 0.004.

Mechanical behavior of tropical Glued Laminated Timber beams with fingers joints

This paper presents an experimental investigation on Glued Laminated Timber (GLT) beams made with two tropical woods species, for structural purposes. Two tropical wood species with different density and under-exploited were chosen. These are Dacryodes buettneri (Ozigo) and Pterocarpus osun (Padouk), Ozigo species was taken as a reference species. A Phenol Resorcinol Formaldehyde (PRF) adhesive resistant to harsh tropical environments was used for bonding. The static bending tests were conducted on beams compound of two and three lamellas with fingers joints. The aims of these tests were to determine the key mechanical parameters such as Module of Rupture (MOR) and the Module of Elasticity (MOE). Influence of the finger’s joints on the bending strength of the GLT beams is also investigated in this work. The results show that the position of lamella and finger joint has an impact on the loss of bending strength of the specimens tested, but they have no influence on their stiffness properties.

Bending and shear performance of cross-laminated timber and glued-laminated timber beams: A comparative investigation

In mass timber construction, cross-laminated timber (CLT) and glued-laminated timber (GLT) usually build a load-bearing system together. Exploring the mechanical properties of CLT and GLT can provide a better understanding and inspiration for designing their members. This study presents a comparative study on the bending and shear characteristics of CLT and GLT beams under the out-of-plane and in-plane loading forms. A series of mechanical properties parameters in the major strength direction were obtained through the tests, and the bending properties were compared with theoretical results. A contribution rate model was developed to quantify the effects of the bending stiffness relationship between adjacent layers in the major strength direction. Under same loading forms, the CLT presented lower bending and shear properties in the major strength direction than the GLT, mainly due to the orthogonal structure inside the CLT. The shear analogy theory showed higher accuracy in the out-of-plane bending results, and the calculation theory that considered all layers could better predict the in-plane bending results. Furthermore, the proposed contribution rate model was consistent with the test results, and it intuitively revealed the effect of the layer stiffness on the overall stiffness for bending specimens under two loading forms.

Bending test on large-scale GLT beams with well-known beam setup using machine grading indicator

ABSTRACT This paper presents large-scale bending test, up to 19 m length, on glued laminated timber (GLT) beams with well-known beam setup and a model to predict the tensile strength of finger joint connections (FJ). Machine graded timber boards, with information about the dynamic stiffness and local knottiness were used to fabricate 12 GLT beams. The position of the timber boards were tracked throughout the GLT fabrication. To quantify the quality of the FJ additional FJ were fabricated and tested in tension. Based on the results, a model to predict their strength properties based on the grading information of the involved timber boards was developed using maximum likelihood estimation for censored data.

Mechanical properties of Glued-laminated timber made up of mixed tropical wood species

ABSTRACT This paper deals with an innovative experimental study performed on glued-laminated timber (GLT) beams, machined and made with three tropical hardwood species. Defect-free beams were obtained by combining alternatively the lamellas taken from the densest to the least dense species, to have TRIO and DUO specimens. Then, static 3-point bending tests were performed on these beams, to assess their mechanical properties and their reliability. Finally, the shear strength tests of the various glue joints are done to understand the failure mode of the beams observed during the bending tests and their impact on the mechanical behaviour of the GLT beams tested. The results show for the two types of GLT (DUO and TRIO’s beams) studied here that: (i) comparatively to the combinations of two lamellas (DUO’s beams), by taking into account the solid woods and homogeneous beams as references, beams with three lamella combinations (TRIO’s beams) present the best mechanical characteristics; (ii) There is a significant influence of the individual lamella’s position or the type of lamella on the global behaviour of the GLT’s beams. Moreover, the advantages of this type of timber beam material are investigated and shown herein.

The Experimental Timber–UHPC Composite Bridge

This paper describes the development of an innovative timber–concrete composite bridge system and especially focuses on the evaluation of the load tests of an experimental bridge structure. The load-bearing structure was designed as glue-laminated timber beams connected with only 60-mm-thick precast bridge deck segments made of ultra-high-performance concrete (UHPC). To verify the production details and behavior of the designed structure, we built a full-scale experimental structure and performed a load test. The load test was arranged as a four-point bending test. First, we performed the overall load test until failure. Some bridge deck segments were consequently cut from the structure in order to run further load tests of the bridge deck in the transversal direction. The results of the experiments were evaluated in detail and compared with analytical calculations.

EVALUATION OF IMPACT OF ELEVATED TEMPERATURES ON YOUNG’S MODULUS OF GLT BEAMS

The influence of elevated temperatures on mechanical behavior of glued laminated timber beams is examined on the basis of tensile tests. Dog bone samples prepared from beams exposed to fire of variable duration were categorized with respect to the type and position of the failure crack, type and number of discontinuities such as knots, and the level of browning. The acquired experimental results suggest that the wood variability and the effect of growth discontinuities are probably more significant than the effect of elevated temperatures. To support this conclusion, further study is currently under way, exploring samples from the second series of the fire tests.

Study on the strength of glued laminated timber beams with round holes: difference in structural performance between homogeneous-grade and heterogeneous-grade timber

Various design codes and design proposals have been proposed for glued laminated timber beams with round holes, assuming that the entire beam is composed of homogeneous-grade timber. However, in Japan, glued laminated timber composed of homogeneous-grade timber is rarely used for beams. In this study, the difference in the load-bearing capacity of glued laminated beams composed of homogeneous-grade timber and heterogeneous-grade timber with round holes when fractured by cracking was investigated experimentally and analytically. The materials used in the tests were glued laminated beams composed of homogeneous-grade Scots pine timber with a strength grade of E105-F345 and heterogeneous-grade Scots pine timber with a strength grade of E105-F300. Experiments confirmed that although the glued laminated beams composed of heterogeneous-grade timber have a lower material strength in the lamina with holes, its resistance to fracturing due to cracks associated with the holes is almost the same as that of the glued laminated beams composed of homogeneous-grade timber. The stresses acting on the holes in the laminated timber with holes of less than half the beam height were lower in the glued laminated beams composed of heterogeneous-grade timber than in the glued laminated beams composed of homogeneous-grade timber. The ratio of the stresses was found to be approximately equal to the ratio of the maximum bending stress or the maximum shear stress acting on the inner layer lamina, as determined by Bernoulli–Euler theory.

The Effect of Glue Cohesive Stiffness on the Elastic Performance of Bent Wood-CFRP Beams.

This paper presents experimental, theoretical and numerical studies of wood-CFRP beams bonded with polyurethane (PUR) adhesive. The analyses include two types of CFRP (carbon fibre-reinforced polymer) strengthening configurations and pure glue laminated timber beams as a reference. Through detailed analyses of a double-lap connection on blocks with and without CFRP strips, the authors state that neglecting the cohesive stiffness of adhesive layers may lead to an overestimation of an overall beam’s stiffness. This is significant with wood–CFRP connections, which showed values two times lower than with wood–wood connections. Theoretical modelling of the equivalent area used in a theory of composites provided much stiffer behaviour of the beams than in laboratory experiments. It proves that a PUR glue eliminates the possibility of using simple models that assume a perfect connection between bonded parts. These conclusions led the authors to use the finite element method (FEM) to take into account the cohesive stiffness. The FEM, based on the properties obtained from a double-lap joint analysis, allowed for the precise prediction of the elastic stiffness of the beams.

Development and structural behaviour of adhesive free laminated timber beams and cross laminated panels

Glued-laminated timber (glulam) beams and cross-laminated timber (CLT) panels are increasingly being used as structural members for buildings, because of their excellent mechanical properties, ability to be processed into larger structural sections and environmental benefits. Nevertheless, the inclusion of adhesives during their production raises environmental concerns due to the release of Volatile Organic Compounds (VOCs) and formaldehyde, which also causes difficulties in recycling. This environmental burden has led to the development of adhesive free laminated timber (AFLT) beams and cross-laminated (AFCLT) panels, which are intended to be used as alternatives to glulam beams and CLT panels in structural applications. In this paper, details of the materials and manufacturing processes for the AFLT beams and AFCLT panels are described, followed by the structural tests and the observed failure modes. Furthermore, parametric studies are carried out to investigate the effects of the following factors on the structural response, i.e. lamella species, dowel species, dowel insertion angles, dowel diameters and configurations, number of dowels (or dowel spacing), section sizes and number of interfaces. It is found that the flexural modulus and flexural strength of the 26 AFLT beams and 26 AFCLT panels are in the range of 1.1–5.3 GPa and 19.3–38.2 MPa, respectively. The experimental results are compared with commonly used glulam beams and CLT panels. The results are useful in understanding the mechanical properties of AFLT beams and AFCLT panels fastened with compressed wood dowels, and constitutes useful structural design information for future construction and structural applications, as well as providing data to validate the finite element modelling. In addition, the study has demonstrated a practical and sustainable approach in timber construction, which may lead to a substantial reduction in the use of structural adhesives and environmental benefits.

Towards enhancing the post-peak performance of glued-laminated timber beams using multi-directional fibre reinforced polymers

An experimental program, investigating the potential of using multi-directional fibre-reinforced polymers (FRPs) as a strengthening option for glulam beams when subjected to blast loading, was undertaken. A total of ten different retrofit configurations were investigated and compared to the behaviour of unretrofitted glulam members. In general, the use of multi-directional GFRP contributed to significant performance enhancement, where ductility ratios in the range of 2.3–3.6 were obtained. The use of bidirectional GFRP fabrics localized the damage in the wood section to a small area, and provided confinement which helped delay the failure of the retrofitted specimen. The FRP fabrics also contributed to an increase in wood ultimate tensile failure strain.A two-step approach was proposed to predict the resistance function of the retrofitted specimens. The model predicted the peak resistance and deflection at peak resistance reasonably well. The approach was able to predict the ultimate failure deflection when the experimental ductility ratios were used. An approach for design using a lower-bound ductility ratio was proposed.

RESPONSE AND DAMAGE EVOLUTION OF SINGLE EDGE NOTCHED TIMBER BEAMS UNDER THREE-POINT BENDING

Two groups of small-size single edge notched beams (SENB) made of European spruce (Picea abies) were tested in three-point bending (3PB) until failure under displacement control. The first group comprised of eight solid and two glued laminated (GL) timber beams manufactured with (a) the single edge notch at the bottom of the mid-span and (b) the reduced ligament depth. The second group consisted of four GL timber beams with the single edge notch only. We employed digital image correlation (DIC) to quantify strains and displacements, capture the damage evolution, and track the sequence of failure patterns. In this work, we present response of the beams in terms of load vs. crosshead displacement of the moving crosshead and load vs. crack tip opening displacement (CTOD).

EXPERIMENTAL INVESTIGATION OF LOAD-BEARING CAPACITY AND DEFLECTIONS OF FULL-SCALE GLUED LAMINATED TIMBER BEAMS

With the transition to the design of timber structures in accordance with European standards, problems arise in assessment of the load-bearing capacity of glued timber structures that are caused by insufficient amount of data about the physical, mechanical and deformation properties of glued timber, which is produced in Ukraine. The aim of the work was to determine the load bearing capacity in bending and deflection of a glued timber beam under the action of a concentrated load in the middle of the span. Two glued laminated timber beams were used in the experiment. Both beams were made using lumber from pine wood and a moisture-curing onecomponent polyurethane adhesive Kleiberit PUR 510 FiberBond. The beams have the dimensions of the cross-section: width of 120 mm and height of 180 mm. The length of the beams was 9880 mm. Each beam consisted of 9 layers of 20 mm thick lamellas glued together. Considering the absence of the data on the strength class of the beam material, the theoretical load bearing capacity and deflection were determined according to the characteristics of the GL24h class (minimum strength class), and amounted to 722 kgf and 19.1 cm, respectively. As a result of the tests, the failure load and the deflection of the beams were determined, and the dependences of the deflection on the load were obtained. The actual deflection of the beams determined was 251 mm and 275 mm, which is 1.31 and 1.44 times higher than the predicted deflection. Accordingly, the failure load determined experimentally is 1.96 and 2.03 times higher than the theoretical value. During the tests, the features of the deformation and the nature of the destruction of the beams were investigated. Wherein, the determining factor was the presence of defects in timber and lamellas joints along the length in the most stressed layers. Based on the data obtained, recommendations on manufacturing aimed at the increasing the bending strength of glued laminated timber beams are given. The results obtained will be further used in the development of structural solutions for hybrid timber-concrete floors.

STUDY ON STRENGTH OF GLUED LAMINATED TIMBER BEAMS WITH ROUND HOLES

STUDY ON STRENGTH OF GLUED LAMINATED TIMBER BEAMS WITH ROUND HOLES

Experimental investigation of glued-laminated timber beams with Vectran-FRP reinforcement

The growing interest in sustainable buildings has inspired the improvement of timber structures in the construction market. As a raw material, wood may present natural defects that can cause changes in its mechanical properties, such as strength reduction, as well as brittle failure under tension, which limit the application of this material in construction. In recent decades, synthetic fibers with high tensile strength are available as construction material, and research to evaluate the efficiency of synthetic fibers and adhesive composites as a reinforcement for glued-laminated timber beams has been carried out. This paper deals with an experimental study applying bending tests to glue-laminated timber beams made of Pinus Elliottii, a low-strength wood class originated from reforestation, and strengthened with fiber reinforced polymers of Vectran fibers and epoxy adhesive. A numerical procedure based on the finite element method is also developed to compare with experimental results. Vectran is a synthetic thermoplastic fiber with high mechanical properties, however, its potential application as reinforcement material in structural pieces is still poorly explored. The results obtained in this work demonstrated that the application of Vectran-FRP reinforcement to glued-laminated timber beams provided both an increase of 19.48 to 34.95% in elastic regime stiffness and of 7 to 40% in ultimate load, when compared with unreinforced similar beams. Numerical analysis adequately confirmed the experimental results on elastic behavior, while in the non-elastic phase it revealed a considerable difference. A reduction in the rupture coefficient of variation regarding the reinforced beams was also verified. In addition, the application of fibers as structural reinforcement changed the timbeŕs failure mode from brittle in tension to ductile in compression. The results show that Vectran fibers are mechanically efficient as reinforcement, with perspectives of application in construction.

Evaluation of Structural Systems for Industrial Dairy Farming Facilities

This paper presents the assessment of conventional structural systems used for industrial dairy farming focusing on the cost and energy consumption. Various structural forms for industrial dairy farming were investigated considering dozen of structural models and materials. Eleven different structural systems were compared in terms of cost and energy consumption. Steel girders, steel columns, glued-laminated timber, reinforced concrete (RC) columns and steel trusses were used in this research as the structural components and materials. The SAP2000 software was used for the analysis of the modeled structures. The obtained results of the analyses demonstrated that the use of RC members or prefabricated concrete components is economically advantageous, while the use of glued-laminated timber was the least economical alternative. The highest cost was observed for a structural model fabricated with a conventional Gable steel frame and the lowest cost was observed for a structural model made of a 2-span twin mono-pitch Portal frames constructed with prefabricated RC beams and columns. However, the lowest energy consumption was observed for a structural model constructed with a single-span twin mono-pitch Portal frames constructed with RC columns and glued-laminated timber beams and the highest energy consumption was observed for the structural model fabricated with a conventional Gable steel frame, which had the highest cost.

Monitored Indoor Environmental Quality of a Mass Timber Office Building: A Case Study

A broad range of building performance monitoring, sampling, and evaluation was conducted periodically after construction and spanning more than a year, for an occupied office building constructed using mass timber elements such as cross-laminated timber (CLT) floor and roof panels, as well as glue-laminated timber (GLT) beams and columns. This case study contributes research on monitoring indoor environmental quality in buildings, describing one of the few studies of an occupied mass timber building, and analyzing data in three areas that impact occupant experience: indoor air quality, bacterial community composition, and floor vibration. As a whole, the building was found to perform well. Volatile organic compounds (VOCs), including formaldehyde, were analyzed using multiple methods. Formaldehyde was found to be present in the building, though levels were below most recommended exposure limits. The source of formaldehyde was not able to be identified in this study. The richness of the bacterial community was affected by the height of sampling with respect to the floor, and richness and composition was affected by the location within the building. Floor vibration was observed to be below recognized human comfort thresholds.

CHEMICALLY TREATED GLUED LAMINATED PARICÁ TIMBER (Schizolobium parahyba var. amazonicum)

ABSTRACT In the production of glue-laminated timber (GLT), boards derived from planted forest wood with easy workability are glued on top of one another. The main objective of the present work was to evaluate the performance of parica timber GLT beams (5 × 10 cm) on GLT. Three procedures were performed: (1) GLT beams (5 × 10 cm) were produced using natural lamellae without chemical preservatives; (2) the individual lamellae (2.5 × 5 cm) were chemically treated, and then glued together; and (3) the beams formed from the glued natural lamellae (5 × 10 cm) were treated chemically. The positions of lamellae on the beams were determined by their modulus of elasticity values (MOE), which were estimated by a non-destructive bending test with a three-point load. The analytical bends, determined by the homogenized section method, and the experimental bends, measured by the four-point bending test, were compared. The differences between the bends were statistically evaluated, and it was found that the experimental bend (21.65 mm) was less than the analytical bend (34.02 mm). There was no significant loss of shear strength or MOE. The axial strength of the chemically untreated beams (49.18 MPa) was significantly higher than that of the untreated beams fabricated from natural lamellae (40.48 MPa). The results indicate that the gluing of treated lamellae does not affect beam performance.