Laminated Timber Beams Research Articles

Experimental stiffness investigation of finger joints in glued laminated timber beams using digital image correlation

Glued laminated timber (GLT) is an engineered wood product widely used in structural applications. The mechanical properties of the GLT beams significantly depend on the mechanical properties of local weak sections such as knots and finger joints (FJs). Conventionally, the mechanical behavior of the local weak sections has been mainly investigated in the individual lamellae. In the present study, their mechanical behaviors within the GLT beams are investigated. 22 GLT beams with well-known beam setups in four-point bending tests were studied. Digital image correlation was used to measure displacements and strains in the region of the beams with the constant bending moment. This paper presents the strain distributions in the GLT beams and discusses the influence of the timber board arrangements and, accordingly, the knots and the FJs. As expected, the strain distributions of the GLT beams vary significantly. Depending on the arrangement of the knots, they can cause strain concentrations in the beams, which can be distributed to the adjacent lamellae. FJs do not cause significant strain concentrations; however, they can influence the strain distribution along the lamellae. Furthermore, a reduced stiffness of the FJs, compared to the connected timber boards, is identified.

Verification and Validation of finite element models for laminated timber structures using solid, solid-beam and solid-shell approaches

This paper presents a numerical approach to assess efficiently the vibration performance of adhesive-free engineered wood products assembled through compressed wood dowels. Predictive finite element models are obtained by applying the Verification and Validation methodology. The models are first developed using solid elements. Then, solid-beam and solid-shell approaches based on standard solid elements are developed with first-order or higher-order theories. Beam or shell kinematic assumptions are applied throughout the cross-section of the dowels and through the thickness of the layers. From a numerical point of view, a modification of the system of algebraic equations, based on the concept of independent and dependent nodes, is developed. Dependent nodes are eliminated, resulting in a significant reduction in the number of degrees of freedom and floating-point operations. The methodology is evaluated for the calculation of frequencies and mode shapes of adhesive-free laminated timber beams and timber panels with a mix of solid elements, solid-shell and solid-beam approaches. The study highlights the efficiency of the proposed modelling approach in terms of quality of results and model size reduction.

Definition of the stress-strain state of a glued laminated timber beam reinforced with composite strips using experimental method

The trend in the development of the construction industry worldwide requires increasing attention to ecological aspects, which means that materials with minimal negative impact on the environment are becoming increasingly popular. At the same time, these materials must possess high strength and durability against various external influences and loads. From this perspective, constructions made of wood and its derivatives are gaining the most popularity. Such constructions, made from renewable natural resources, exhibit relatively high strength at relatively low density, thus belonging to such materials. Although wood has its drawbacks, such as susceptibility to drying, rotting, and anisotropy of properties, these drawbacks can be completely mitigated in glued laminated timber structures. Glued laminated timber beams, which are the primary structural element of many buildings and structures, are the most widespread. Therefore, the issue of significantly increasing their rigidity and strength through reinforcement with composite materials is particularly relevant. This article proposes a methodology for determining the stress-strain state of a glued laminated timber beam reinforced with composite strips. The results include deformation parameters of the experimental model, actual elastic modules during bending, maximum longitudinal stresses at the center of the span, along the load application axis, and along the support axis. Additionally, maximum transverse and shear stresses along the load application axis and along the support axis are determined. The actual maximum load-bearing capacity of the experimental model reinforced with composite strips is established.

Experimental investigation of the shear force capacity of prismatic cross laminated timber beams

Experimental tests of Cross Laminated Timber (CLT) under in-plane beam loading conditions are presented. The influence of the element layup, the individual lamination width, and the beam overhang at the supports on the shear force capacity was investigated. All the CLT beams had the same gross cross section, and a 4-point-bending test setup was used. The experimentally determined load-bearing capacities are compared with the load-bearing capacities resulting from analytical methods proposed for structural design, focusing on shear failure in the crossing areas of flatwise bonded laminations (shear failure mode III). The test results indicate no or very small influence of the element layup and the lamination width on the shear force capacity. These results partly contradict the predictions of the proposed design methods. Of the three studied beam geometry parameters, the beam overhang at the support had the greatest influence on the load-bearing capacity.

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.

Application of Composite Bars in Wooden, Full-Scale, Innovative Engineering Products-Experimental and Numerical Study.

The commercialization of modular timber products as cost-effective and lightweight components has resulted in innovative engineering products, e.g., glued laminated timber, laminated veneer lumber, I-beams, cross-laminated timber and solid timber joined with wedge joints. With the passage of time, timber structures can deteriorate, or new structural elements are required to increase the stiffness or load-bearing capacity in newly built structures, e.g., lintels over large-scale glazing or garages, or to reduce cross-sectional dimensions or save costly timber material while still achieving low weight. It is in such cases that repair or correct reinforcement is required. In this experimental and numerical study, the static performance of flexural timber beams reinforced with prestressed basalt BFRP, glass GFRP and hybrid glass-basalt fiber bars is shown. The experimental tests resulted in an increase in the load-carrying capacity of BFRP (44%), GFRP (33%) and hybrid bars (43%) and an increase in the stiffness of BFRP (28%), GFRP (24%) and hybrid bars (25%). In addition to this, glued laminated timber beams reinforced with prestressed basalt rods subjected to biological degradation, 7 years of weathering and prolonged exposure to various environmental conditions were examined, and an increase in the load-bearing capacity of 27% and an increase in stiffness of 28% were obtained. In addition, full-size laminated timber beams reinforced with prestressed basalt bars were investigated in the field as an exploratory test under fire conditions at elevated temperatures, and the effect of the physical-mechanical properties during the fire was examined via an analysis of these properties after the fire. In addition, a satisfactory correlation of the numerical simulations with the experimental studies was obtained. The differences were between 1.1% and 5.5%. The concordance was due to the fact that, in this study, the Young, Poisson and shear moduli were determined for all quality classes of sawn timber. Only a significant difference resulted in the numerical analysis for the beams exposed to fire under fire conditions. The experimental, theoretical and numerical analyses in this research were exploratory and will be expanded as directions for future research.

Impact loading of glued laminated timber beams without finger-joints

Progressive collapse can be triggered by impact loading from vehicles or other objects and propagated by impact loading from falling debris. Therefore, the correct modeling of impact loading is necessary to assess the resistance of a structure against progressive collapse. As the number of timber buildings increases, the importance of adequate considerations of impact loading is growing. Previous research on impact loading of wood or timber was carried out on small clearwood specimens or on single boards. However, modern timber buildings use advanced wood-based composites, such as glued laminated timber and laminated veneer lumber. The characteristics of these materials are widely different from clearwood and single boards. In this paper, energy-based equations are derived for the peak impact force and the dynamic strength increase factor. These are quantified by pendulum impact hammer tests on 95 full-size glued laminated timber beams. The results are applied in a calculation example to demonstrate their potential use in practice.

Experimental and numerical investigation of flexural properties of larch beams reinforced with different layer numbers

Recent applications demonstrated how fiber-reinforced polymer (FRP) composites can improve the structural capabilities of glulam beams, particularly regarding their flexural and shear strength. With the development of precise numerical models, such systems can be optimized. There is currently a dearth of information in the literature on numerical models that can accurately anticipate the nonlinear behavior of low-grade glued laminated timber beams reinforced with FRP. In this study, larch beams were reinforced with carbon fiber reinforced polymer fabric 1, 2 and 3 layers. The effect of the number of floors on the flexural properties of the beams in reinforcement was investigated experimentally and numerically. As a result of the study, the best flexural properties were achieved with 3-layer reinforcement. It was observed that 1- and 2-layer reinforcement compared to the reference beam were also significantly effective. Numerical analyzes gave close values with experimental test results. As a result of comparing the results obtained from the numerical model with the experimental findings, it was concluded that the FRP fabric managed to significantly increase the performance of larch timber. The model is a useful tool for examining the effect of reinforcement coefficient and will be used for optimization of the larch beam.Recent applications demonstrated how fiber-reinforced polymer (FRP) composites can improve the structural capabilities of glulam beams, particularly regarding their flexural and shear strength. With the development of precise numerical models, such systems can be optimized. There is currently a dearth of information in the literature on numerical models that can accurately anticipate the nonlinear behavior of low-grade glued laminated timber beams reinforced with FRP. In this study, larch beams were reinforced with carbon fiber reinforced polymer fabric 1, 2 and 3 layers. The effect of the number of floors on the flexural properties of the beams in reinforcement was investigated experimentally and numerically. As a result of the study, the best flexural properties were achieved with 3-layer reinforcement. It was observed that 1- and 2-layer reinforcement compared to the reference beam were also significantly effective. Numerical analyzes gave close values with experimental test results. As a result of comparing the results obtained from the numerical model with the experimental findings, it was concluded that the FRP fabric managed to significantly increase the performance of larch timber. The model is a useful tool for examining the effect of reinforcement coefficient and will be used for optimization of the larch beam.

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%.

Experimental assessment of self-tapping screws for the reinforcement of multiple holes in laminated veneer lumber beams

In recent times, there is increased focus in the built environment on the use of low carbon materials. In tall timber buildings, service ducting needs to be facilitated. Multiple holes in elements may be required in buildings where a high demand of services exist. Limited investigations have been conducted on laminated veneer lumber (LVL) beams in comparison to the literature on timber and glued laminated timber beams and no experimental testing has been conducted where multiple holes in LVL have been reinforced. Such openings are of particular concern when positioned in high shear zones. Therefore, an experimental programme in which seventy-five LVL beams were monotonically tested in three-point bending was conducted. The programme included standard beams, beams with a single round hole, and beams with double round holes for three different hole diameters and two holes spacings. The openings were concentrically positioned and were reinforced using internal screw reinforcement in which three configurations were examined. The programme was designed to evaluate the guidance that is currently available which has been developed based on testing with glued laminated timber. Throughout, it was seen that the self-tapping screws orientated at 60° were the most effective in comparison to when the reinforcement was orientated at 45° or positioned vertically. For LVL beams with single holes and up to hole diameters of 0.45 diameter (d) which far exceeded the current guidance of 0.3d maximum hole size, the reinforcement when positioned at 60°, achieved midspan failures like standard beams. The failure loads of such reinforced beams were in the same range as the standard beams. The screw reinforcement when orientated at 60o, was most effective for the double holed beams when a hole size of 0.35 d for both spacings (0.5 d and 0.75 d) was studied. The load carrying capacity was also in the same range as the standard beams but the failure mode was hole edge failure. Strain profile readings indicated the effectiveness of the reinforcement such that strains at the soffit of the beam where two holes were reinforced with screws exceeded the strains at the soffit of the standard beams.

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.

Comparison of behaviour of burnt beams models with effective and actual residual cross-sections in three point bending test

Glued laminated timber beams exposed to fire of a variable duration were tested in three point bending. Three types of model geometries taking into account the effect of burning were created. Each model was examined for five material data sets. The maximum deflection obtained from FEM simulations was compared with the corresponding deflection wel derived from a three point bending test of burnt beams. The analysis was performed with the help of Ansys® software limiting attention to a liner elasticity with the maximum applied force Fel selected at the proportionality limit observed experimentally. Majority of FEM models provided smaller deflections compared to measurements except for the material set adopting Young’s moduli from the compression test. The best fit was observed for the material data set obtained from homogenization. No predominant preference among individual geometries was found promoting the computational model based on reduced cross-section as sufficiently accurate.

Augmented Reality for high precision fabrication of Glued Laminated Timber beams

In recent years, the utilization of Augmented-Reality (AR) within the construction industry has increased. However, high-precision applications such as glulam beam fabrication requires tolerances of less than 2 mm, which is smaller than what current AR workflows can offer. This research investigates the use of QR-Code Markers on glulam beams to encode additional positional data in the environment to better interpolate between the physical space, the glulam beam, and the headset. The objective is to understand the effects of Marker placement, size, and frequency on the accuracy of AR projection for glulam fabrication. This paper describes the AR workflow, the effects of Markers, and the framework the Twinbuild software for drift correction in large-scale AR applications. The method can achieve an average tolerance as low as 0.97 mm when Markers are placed in 1.25 ft. increments along the beam edge. The research demonstrates the viability of AR for high-precision fabrication applications.

STUDY ON STRENGTH OF GLUED LAMINATED TIMBER BEAMS WITH TWO ROUND HOLES

STUDY ON STRENGTH OF GLUED LAMINATED TIMBER BEAMS WITH TWO ROUND HOLES

Catenary action in strip-reinforced wood and timber beams

At present, the popularity of timber as a structural material is booming. However, the current knowledge on disproportionate collapse prevention and extreme loading of timber buildings is scarce. To prevent disproportionate and progressive collapse, catenary action is an important mechanism, where the axial capacity of bending members is activated. Because of the brittle behavior of timber in the relevant failure modes, it can only achieve catenary action via strengthening. In this paper, analytical expressions are derived for the elastic, plastic, and catenary capacity of laterally loaded wood and timber beams with a tension-side strip reinforcement. A load-path dependent M-N interaction diagram with damage accumulation explains the ultimate catenary capacity and the transition between the bending- and catenary-dominated load-carrying mode. The analytical expressions are validated and discussed based on tests on beech clearwood specimens reinforced with carbon fibers in a polyurethane matrix. Furthermore, a case study on glued laminated timber beams is presented to demonstrate the potential of reinforcing timber beams subjected to extreme loading.

Strukturne i projektirane vrijednosti lameliranih greda i greda od cjelovitog drva Dipteryx panamensis i Hieronyma alchorneoides s brzorastućih plantaža

Dipteryx panamensis and Hieronyma alchorneoides are two species of high specific gravity used in reforestation programs in Costa Rica, but they lack products with structural value for commercialization. In order to introduce the wood of these two species in the market, the objective was established to study the behavior of solid timber beams and glued laminated timber beams of two cross sections (2 cm × 10 cm and 2 cm × 15 cm) and establish the design values in bending test. The results showed that the bending design values (fb) ranged from 2 to 26 MPa in glued laminated timber beams, while in solid timber beams, fb ranged from 6 to 15 MPa. In the shear design values (fv), the variation was from 0.29 to 0.67 MPa in glue laminated timber beams and from 1.80 to 2.58 MPa in solid timber beams. It was also found that the D. panamensis beams showed higher values than H. alchornoides beams. Finally, it was established that glued laminated timber beams showed better performance in bending parameters and higher design values, resulting in wider span values, than solid timber beams when used in floor and roof construction.

A criticism on strengthening glued laminated timber beams with fibre reinforcement polymers, numerical comparisons between different modelling techniques and strengthening configurations

The application of CFRP for strengthening timber structures has proven its efficiency in enhancing load-bearing capacity and, in some cases, the stiffness of structural elements, thus providing cost-effective and competitive alternatives both in new design and retrofitting existing historical buildings. In this study, glued laminated timber beams strengthened with CFRP were examined. A number of test beams with different reinforcement configurations and beam sizes were selected from the literature. These beams were analysed with three different methods as numerical, theoretical and code perspective. For the numerical method, a 3D nonlinear finite element model which includes damage and fracture mechanics was constructed. All test beams were studied with different methods and results were compared with respect to initial flexural stiffness, midspan vertical displacement and failure load. The effectiveness of methods and strengthening configurations were stated and suggestions for practical application of FRP-strengthened timber beams were presented.

Numerical Investigation of Glue Laminated Timber Beams considering Reliability-based Design

Numerical Investigation of Glue Laminated Timber Beams considering Reliability-based Design

Engineering method of calculating laminated timber elements reinforced with composite tapes

Annotation. In today's world, construction requires environmentally friendly materials that cause minimal damage to the environment. At the same time, they must have great strength and be resistant to various types of external influences. Timber structures, which are made of renewable natural materials and have a relatively high strength, can rightfully be considered as such material. Despite the fact that timber itself has certain negative properties, namely the tendency to shrink and swell, rot, anisotropy of properties, which requires special attention in construction, in laminated timber structures (LTS) these disadvantages are already more manageable. Beams are one of the main laminated timber structures. Laminated timber beams reinforcement allows to significantly increasing their stiffness and strength.
 The article proposes a methodology for calculating laminated timber elements of rectangular section reinforced with composite tapes. Refined formulas for determining the efficient geometric and mechanical characteristics are provided. The proposed method was compared with another analytical method of calculation and with the numerical method of modeling in the LIRA-CAD software complex using the finite element method. It was proved that this method of reinforcing laminated timber structures is promising and relevant.

OpenSeesdevelopment for modelling timber structural members subjected to realistic fire impact

AbstractTimber buildings have been preferred in many regions for the sustainable nature of timber material. Although engineered timber products become promising alternates to traditional construction materials, the fire safety of timber buildings remains a key barrier to wider use. Currently, the design of timber structures mostly adopts the Eurocode 5 approach, which estimates the heat transfer or char depth under the premise of standard fire exposure. To investigate the behaviour of timber structural members in the context of realistic fire action in compartments, appropriate models for different stages of numerical simulation are needed. A series of development have now been conducted in the open‐source platform OpenSees, which enables modelling the heat transfer of timber sections in non‐standard fire scenarios and thermo‐mechanical analysis model using either beam elements or shell elements for various timber structural members. Corresponding thermal actions are developed to deal with timber slabs in fire or timber beams subjected to three‐side fire exposure. Tests on cross‐laminated timber beams at ambient temperature and under fire exposure are modelled to validate the developed capabilities, which is followed by modelling a glued laminated timber beam heated by furnace. In the end, a timber‐concrete composite slab is modelled using the fire impact from a Computational Fluid Dynamics model, which demonstrates the current vision of modelling timber structures in fire and OpenSees for fire is committed to providing such an open‐source research platform to support further modelling work.