Laminated Timber Beams Research Articles

Dynamic behaviour of a timber footbridge with uncertain material properties under a single deterministic walking load

The dynamic study of a short span timber footbridge with uncertain mechanical properties under the action of a deterministic walking load model which represents one individual is presented. The aim of the work is to quantify the influence of the uncertain material properties in the natural and forced vibration problems of a short span timber footbridge. These structural systems made of timber are increasingly employed due to the high stiffness/weight ratio that this material exhibits. This feature can lead to lightweight structural systems in which the acceleration levels can exceed the human comfort limits. The assumed sources of uncertainties of this structural model are the Modulus of Elasticity (MOE) and the mass density. Also, the geometrical design of the boards that compose the laminated timber beams supporting the floor involves variability of the distances between finger joints. Probability Density Functions (PDFs) of the timber properties are formulated from the Principle of Maximum Entropy (PME). The finger joints distance generates the lengthwise variability of the MOE and the mass density in each board of the laminated beams. The PDFs of the natural frequencies of the structure, the mode shapes and the structural response are numerically obtained through the Finite Element Method (FEM) and statistic tools. In order to carry out this analysis, plate and laminated beam elements derived from the First Order Shear Deformation Theory (FSDT) are employed. The variation of the effective stiffness and mass along the elements due to the union of boards with different properties produces an important reduction of the standard deviation of the natural frequencies. The conditions in which the stochastic properties of the structure lead to unacceptable acceleration levels are studied. In some scenarios, the variation of the material properties can lead to unacceptable serviceability performances of the structure and a reduction in the pedestrian comfort, according to the codes in force. However, new design guidelines replace the line limits by comfort regions which are also discussed here.

Stochastic engineering framework for timber structural elements and its application to glued laminated timber beams

Due to the natural growth process of trees, wooden boards show a high amount of random fluctuation in their mechanical properties. Currently, in engineering practice, a homogeneous material behaviour is assumed within wooden boards and uncertainties in loading and load-bearing capacity are considered through design procedures based on partial safety factors. These partial safety factors are not directly linked to the individual mechanical behaviour of the considered structural system/element. Thus, a stochastic framework opening up the possibility to establish such links, by combining structural analysis tools with probabilistic descriptions of wooden boards, could be an important step in timber design, also to improve the competitiveness of wood against other building materials.In this study, a framework able to consider the impact of random stiffness fluctuations of wooden boards on the performance of glued laminated timber (GLT) is presented. A 2D finite element model is employed to depict the interactions between individual laminations. It is tightly integrated into a commercial robustness analysis and optimisation software package.The mechanical properties of each board are obtained on basis of measurements collected during the grading process and are condensed into so-called stiffness and strength profiles. Based thereon, a probabilistic material model is developed for the random generation of an arbitrary number of stiffness and strength profiles. On basis of the probabilistic material model and the mechanical FE model, the sensitivity to changes in the design can be explored. Subsequently, an adaptive response surface approach leads to the optimal design parameters of the user-defined structure.An exemplary application scenario shows the workflow for determining the optimum hole dimensions and location in a GLT beam. The material model indicates large scatter in the mechanical properties, leading to conservative results. Nonetheless, and although only bending failure of GLT beams and no finger joints are taken into account, the example shows the strengths of the employed workflow from sensitivity analysis to best designs.

Numerical analysis of glued laminated timber beams reinforced by Vectran fibers

Abstract Some factors, such as environmental actions and load increases, can cause a necessity to restore a structural element. An efficient method typically used is to reinforce the structure with a high mechanical property´s material. In this study, a numerical approach of glued laminated timber beams reinforced with the following synthetic fibers: Vectran®, carbon and glass fibers was developed. Vectran® fibers have high performance and are employed in various areas, but not yet as a structural reinforcement. The beam models were designed on Ansys software-version 12 and the results were analyzed regarding the maximum stresses and displacements. When compared to unreinforced beam, the fiber reinforcement absorbed a great part of the acting stresses, reducing the tensile stress and the displacement maximum values. Considering mechanical properties and the material cost, Vectran® fiber is an interesting alternative for structural reinforcement, fitting its mechanical performance at an intermediate level between carbon fiber and glass fiber.

Experimental study on glued laminated timber beams with well-known knot morphology

Nowadays, the impact of knots on the failure behaviour of glued laminated timber (GLT) beams is considered by subjecting the single lamellas to a strength grading process, where, i.a., tracheid effect-based laser scanning is used to obtain information about knot properties. This approach single-handedly defines the beam’s final strength properties according to current standards. At the same time, advanced production processes of such beams would allow an easy tracking of a scanned board’s location, but, at this point, previously obtained detailed information is already disregarded. Therefore, the scanning data is used to virtually reconstruct knot geometries and group them into sections within GLT beams. For this study, a sample of 50 GLT beams of five different configuration types was produced and tested under static four-point-bending until failure. As for each assembled lamella the orientation and position within the corresponding GLT beam is known, several parameters derived from the reconstructed knots can be correlated to effective GLT properties. Furthermore, the crack patterns of the tested beams are manually recorded and used to obtain measures of cracks. A detailed analysis of the generated data and their statistical evaluation show that, in the future, dedicated mechanical models for such timber elements must be developed to realistically predict their strength properties. A potential approach, using fluctuating section-wise effective material properties, is proposed.

Deflection behavior and load-bearing period of structural glued laminated timber beams in fire including cooling phase

Purpose This paper aims to discuss the fire performance of glulam timber beams based on their deflection behavior and load-bearing period, which were obtained from load-bearing fire tests under constant load conditions. Design/methodology/approach In this report, the fire performance, primarily deflection behavior and load-bearing period of glued laminated (glulam) timber beams will be discussed from the standpoint of load-bearing fire tests conducted during the cooling phase under constant load conditions. Then, based on the charring depth and the per section temperature transformation obtained from loading test results, the load-bearing capacity of the glulam timber beams will be discussed using the effective section method and the strength reduction factor, which will be calculated in accordance with the European standards for the design of timber structures (Eurocode 5). Findings In the cooling phase, the charring rate is decreases. However, as the temperature in the cross section rises, the deflection is increases. The failure mode was bending failure because of tensile failure of the lamina at the bottom of the beam. Moreover, a gap caused by shear failure in a growth ring in the beam cross-section in the vicinity of the centroid axis was observed. Shear failure was observed up until 1 to 3 h before end of heating. The calculated shear strength far exceeded the test results. Shear strength for elevated temperature of glued laminated timber is likely to decrease than the shear strength in Eurocode 5. Originality/value Unlike other elements, a characteristic problem of timber elements is that their load-bearing capacity decreases as they are consumed in a fire, and their bearing capacities may continue to degrade even after the fuel in the room has been exhausted. Therefore, the structural fire performance of timber elements should be clarified during not only the heating phase but also the subsequent cooling phase. However, there are few reports on the load-bearing capacity of timber elements that take the cooling phase after a fire into consideration.

Novel internally LVL-reinforced glued laminated timber beams with large holes

A novel timber composite is presented, consisting of glued laminated timber (GLT) from softwoods and intercalated cross-layered plates of laminated veneer lumber (LVL) made of hardwood species, specifically beech. The structure is especially suited for beams with multiple, large rectangular holes, where the LVL acts as a highly efficient internal reinforcement and contributes to a damage-tolerant ultimate load behavior. The load capacity of the composite beam is not induced by the stress concentrations at the corners of the hole, which, in contrast to generic GLT, lead to a sudden propagation of cracks and brittle failure. It is shown that the structure, including the holes, can be designed analytically in a transparent manner by using beam theory, a parallel system approach, and modifications from FEM analysis for the verification of tensile forces at the hole periphery. The composite, firstly used in a recent multi-story building in Australia, significantly improves the competitiveness of timber in building works, which have been limited to steel and reinforced concrete structures.

Performance of glue laminated timber beams composed of sengon wood (Albizia falcatara) and coconut wood (Cocos nucifera) with nylon-threads reinforcement

This paper aims to describe the performance of mix-glue laminated timber beams that are given a nylon strapping as external reinforcement with the three-point bending test to three groups of beams based on the span-to-depth ratio, i.e.: G11, G8, and G5 groups. Each group consists of three types of lamination compositions, namely: Type I, whole lamination consists of sengon wood; Type II, the placement of the coconut wood lamination as the outermost; Type III, similar to type II with added nylon straps with a distance of 5 mm. The bending test results show differences in elastic modulus, flexural strength and shear strength of the glue-laminated timber beams. Based on the comparison of glulam beams consisting of six laminations of sengon wood it was found that the placement of the coconut wood as the outermost lamination succeeded in increasing the elastic modulus, the flexural and shear strength of beams by 28%, 13%, and 34%, respectively. In addition, the reinforcement with nylon straps results in the modulus of elasticity, bending and shear strength of glulam to increase by by 41%, 2%, and 49% respectively.

Computer modeling of glued laminated timber beam reinforced with steel bars fixed with epoxy resin

Structures of glued laminated timber have many technical and economic benefits compared to metal or reinforced concrete: lower weight, sufficient strength and durability. Competent design of such structures requires numerical analysis that best meets specified conditions. This article describes a 3D analysis of a beam composed of glued laminated timber, reinforcement bars and epoxy resin. When determining the stress-strain state of the structure, anisotropic properties of wood were also taken into account. Computer analysis of material behavior of timber, reinforcement bars and epoxy resin was performed with the help of ANSYS software package.

Experimental investigation of flexural behavior of glulam beams reinforced with different bonding surface materials

In this study, flexuralbehaviors of glue laminated timber beams manufactured from Pinussylvestristree were investigated by comparing the results with those of massive timber beams. The main variables considered in the study were number of laminations, types of adhesive materials and reinforcement nets used in the lamination surfaces. In scope of the experimental study, glue laminated beams with 5 and 3 lamination layers were manufactured with 90x90mm beam sections. In the lamination process epoxy and polyurethane glue were used. Morever, in order to improve the bond strength at the lamination surface, aluminium, fiberglass and steel wire nets were used at the lamination surfaces. Load–displacement responses, ultimate capacities, ductility ratios, initial stiffness, energy dissipation capacities and failure mechanisms of glue laminated beams were compared with those of massive beams. It was observed that the general bending responses of glue laminated beams were better than those of massive beams. In addition to that the use of reinforcement nets at the lamination surfaces increased the ultimate load capacities of the tested beams. The highest ultimate load capacities were oberved from the tests of glue laminated beams manufactured using five laminated layers and retrofitted with polyurethane glue using steel wire reinforcement nets, in the direction normal to the lamination surface. Finally, the finite element simulations of some test specimens were performed to observe the accuracy of finite element technology in the estimation of ultimate capacities of glue laminated timber beams.

Analysis of the stiffness and load-bearing capacity of glued laminated timber beams reinforced with strands

In this paper a benefit of glulam pinewood beams reinforced strands is discussed. In the first phase, series of pull-out tests were performed on specimens made up of different types of glue (melamine-urea-formaldehyde, epoxy and others) to detect pull-out force and failure mode of a specimens. In the second phase, series of equal cross-section glulam beams with strand and rod reinforcement were theoretically analysed using transformed cross-section method. Additionally, series of experimental testing were made. Benefits of strand reinforcement use as glulam beams’ reinforcement were identified and examined the possibility of one glue type application in all operations of reinforced glulam beams manufacturing.

Evaluation of glue line shear strength of laminated timber structures using block and core type specimens

Monitoring and evaluation of glued laminated timber structures in service is essential to warrant its integrity, where non-destructive techniques play an important role. This paper describes the results obtained on glued laminated timber beams of maritime pine, with and without preservative treatment, and of spruce, exposed to natural outdoor environment as well as to artificial weathering. The assessment of glue lines’ shear strength was investigated through the extraction and testing of cores parallel and perpendicular to the glued lines and block shear specimens with 50 mm × 50 mm and 20 mm × 20 mm shear area. The results highlight the different performances of the various types of specimens tested, showing that the measured shear strength depends on the specimen size and that the size effect depends on the material strength giving a decreasing modification factor with the increase of strength in opposition to the constant factor suggested by standard EN 14080. They also show that shear testing of cores drilled perpendicular to the glued joints may be a promising tool in the assessment of glulam structures on site.

Influences of Scarf-Joint of the Laminae in the Strength and Elasticity of Glued Laminated Timber Beams

The objective of this work is to determinate the influence of the scarf-jointed in the strength and the modulus of elasticity of the glued laminated timber beam. To determine this influence, several tests with the outer laminae with scarf-joint and the bevel with different inclinations has been made. The models were made of Parana Pine, Araucaria angustifolia. For the tests were performed three points bending. With the load values and the deflection at mid-span and by linear regression were determined the effective elastic modulus. The results indicate that the performance is reduced considerably in the presence of a scarf-joint in the external laminae and also the reduction is greater when the scarf angle increases.

Experimental Bending Behavior of Glue Laminated Timber Beams

The aim of this paper is to prove that glue laminated timber is a viable structural material that can easily replace common steel or concrete beams for small and medium spans. It is a much lighter and eco-friendly material with minimal impact on our eco-system by using significantly less energy in it’s production and also by using timber witch is a sustainable material. Experimental four point loading bending tests were conduced on scaled beams according to the EN 408-2010 [1], tests that were meant to study the behavior of these beams under loading and unloading cycles as well as the bending strength and deflection characteristics.

Modeling glulams in linear range with parameters updated using Bayesian inference

A stochastic hierarchical model of a glued laminated timber beam loaded in bending is formulated in this paper. Being attributed to the limited number of observed data the model captures both the inherent variability of the elastic properties of individual timber boards making up the laminated beam and the uncertainty of the parameters controlling their probability distributions. Apart from the deflection measurements obtained from the full scale displacement-controlled, four point bending tests the model also incorporates the data from numerous nondestructive macroindentation measurements. The forward deterministic model of laminated beam is based on the Mindlin beam theory combined with the finite element method to simulate the laboratory measurements numerically. The inference of the model parameters is performed in the framework of Bayesian statistics. Apart from improved posterior distributions of material data, we also offer an improved formula for estimating the longitudinal elastic modulus from indentation measurements.

Quasi-brittle fracture and size effect of glued laminated timber beams

The load bearing capacity of glued laminated timber beams is size dependent. A material based size effect occurs due to the natural variability of the timber properties and can be explained with the Weibull weakest link theory. The Weibull type size effect has received much attention in the timber research community in the past as it is the dominating size effect regarding the load bearing capacity of timber beams. In this paper, it is shown that a further deterministic size effect, which originates from the timber fracture behavior, influences the load bearing capacity of glued laminated timber beams. It is the size effect associated with quasi-brittle behavior. The paper covers a short theoretical review on fracture related size effects and a study comparing experimentally tested beams of several sizes with detailed numerical simulations considering the natural growth characteristics of timber. Further, an analytical model illustrating the features of the fracture related size effect on the load bearing capacity of glued laminated timber beams is presented. It is demonstrated that the simulated load bearing capacity of the tested glued laminated timber beams distinctively improves if the quasi-brittleness is taken into account by using a softening constitutive law.

Fire performance, including the cooling phase, of structural glued laminated timber beams

Purpose Based on heating tests and load-bearing fire tests, this paper aims to discuss the charring rate, the temperature distribution in the section and the load-bearing capacity of structural glued laminated timber beams not only during the heating phase during a 1-h standard fire in accordance with ISO 834-1 but also during the cooling phase. Design/methodology/approach Heating tests were carried out to confirm the charring rate and the temperature distribution in the cross-section of the beams. Loading tests under fire conditions were carried out to obtain the load-deformation behavior (i.e. the stiffness, maximum load and ductility) of the beam. Findings The temperature at the centroid reached approximately 30°C after 1 h and then increased gradually until reaching 110-200°C after 4 h, during the cooling phase. The maximum load of the specimen exposed to a 1-h standard fire was reduced to approximately 30 per cent of that of the specimen at ambient temperature. The maximum load of the specimen exposed to a 1-h standard fire and 3 h of natural cooling in the furnace was reduced to approximately 14 per cent. In case of taking into consideration of the strength reduction at elevated temperature, the reduction ratio of the calculated bending resistance agreed with that of the test results during not only heating phase but also cooling phase. Originality/value The results of this study state that it is possible to study on strength reduction in cooling phase for end of heating, timber structural which has not been clarified. It is believed that it is possible to appropriately evaluate the fire performance, including the cooling phase of the timber structural.

Comparison of Modulus of Elasticity of Glued Laminated Timber

This article focuses on testing of glued laminated timber beams and researching their properties. The article mainly focuses on comparison of measured modulus of elasticity obtained by two different methods. First method used was method of spike which has non-destructive character. This method was used to measure properties of glued laminated timber (GLT) on macro mechanical level in form of modulus of elasticity. Second method was used to determine micromechanical properties of material and is called nanoindentation. Tested material will be also described the article along with principle of testing and presenting results. Those results of individual measurements will be compared with respect to percentage representation of individual phases on micromechanical levels to measurement on macromechanical level.

Javaslatok rétegelt-ragasztott fatartók tervezéséhez, gyártásához és üzemeltetéséhez, felmérési és modellezési eredmények alapján, III. rész: A tönkremeneteleket igazoló vizsgálatok és eredményei

<p class="p1">A rétegelt-ragasztott fatartók egyre elterjedtebbé váltak az elmúlt 50 évben. A megfelelő minőségű anyagokból készített rétegelt-ragasztott tartók minőségi beszerelést és üzemeltetést követően időtállóak, azonban egyre több esetben fordul elő a rétegelt-ragasztott tartók károsodása és a károsodás miatt egész tetőszerkezetek életveszélyessé válása. Ebben a cikkben a rétegrepedések és tönkremenetelek okaihoz kapcsolódó mechanikai vizsgálatok és azok eredményei kerülnek bemutatásra.<br /> A mechanikai vizsgálatok célja, hogy próbatest szinten megállapítsuk a ciklikusan változó klimatikus környezet (hőmérséklet, páratartalom) hatását az RR tartók faanyagára és annak ragasztási síkjaira. Mivel a faanyag rostra merőleges húzószilárdsága és nyírószilárdsága csekély, a tartókon kialakult delamináció oka, ezen feszültségek szilárdságot meghaladó mértékében keresendők. Az elvégzett vizsgálatok is a két szilárdság meghatározására ill. a ciklikusan változó klimatikus környezet ezen szilárdságokra gyakorolt hatására irányultak.</p>

Influence of Lamellar Thickness on Strength and Stiffness of Glued Laminated Timber Beams of Pinus oocarpa

Glued laminated timber is a structural engineered product that requires precision and strict quality control in its manufacture. For ensure that produced elements properties are in compliance with regulatory requirements, final product must be tested under laboratory conditions. Determining factors in final glulam pieces cost are the type and the quantity of adhesive used in structural elements manufacture. This study aimed to investigate, aided by three point static bending tests and variance analysis (ANOVA), influence of glue lines (3, 5, 7) and lamellae (4, 6, 8) on strength (MOR) and stiffness (MOE) properties of glulam beams manufactured with <i>Pinus</i><i>oocarpa</i> (CCA treated) and bonded with Phenol Resorcinol resin (Cascophen RS-216-M). These beams presented nominal dimensions 90mm wide; 100mm height; and 1350mm length. For 100 mm fixed height, three beams configurations were tested (a) with four lamellae of 25 mm (3 glue lines); with 6 lamellae of 16,7 mm (5 glue lines) and 8 lamellae of 12.5 mm each (7glue lines), being fabricated 6 beams for experimental condition. In addition to investigating influence of glue lines and lamellae number, possibility of estimating MOE and MOR based on apparent density was also evaluated. ANOVA results showed no significance about glue lines number (or lamellae thickness) in strength and stiffness values, implying, for economic reasons, be configuration with four 25mm lamellae the best among tested beams. From regressions, apparent density was only significant in MOE estimating (R<SUP>2</SUP> = 46.90%), indicating not be possible to estimate the stiffness and strength values of the glued laminated timber evaluated by the apparent density.

Pulse Method Used for Non-Destructive Assessment of Glued Laminated Timber Beams

This text is focused on GLULAM (glued laminated timber) beams and determination of their properties. This text is mainly focused just on part of more complex research of glued laminated timber beams. This text is focused on pulse method, which is used to determine the dynamic modulus of elasticity of GLULAM beams. This text will describe how the pulse method works, with basic description, describes the tested material and compare the results of testing. In the conclusion we discuss the results, make conclusions and describe the way of our further research of glued laminated timber beams.