Glued Laminated Timber Beams Research Articles

Cold temperature effects on the impact behaviour of glued-laminated timber beams

Engineered wood products, such as glued-laminated timber (glulam), have been and are continuously being utilized in the construction of tall timber buildings and notable landmark bridges. This infrastructure, particularly the latter, may be exposed to hazardous impact loads throughout their service life. As little research has been conducted on the impact behaviour of glulam beams under cold temperature conditions, there is a need to investigate the potential effects of impact loading on glulam structural elements at cold temperatures. This paper presents an experimental investigation aimed at understanding the effects of cold temperatures on the impact behaviour of glulam timber beams. Fifteen glulam beams were tested under quasi-static and impact loading, under ambient and cold temperatures. Drop weight impact testing was performed to simulate dynamic loading conditions similar to those experienced in real-world scenarios. The results indicate that both the loading regime and cold temperatures have a significant influence on the strength and stiffness of glulam beams, whereby statistically significant increases in the moduli of rupture and elasticity were observed, however, no interaction between the two variables occurred. A single-degree-of-freedom (SDOF) model was developed and validated using the experimental test results and found to provide good accuracy.

Analysis of the Bending Behaviour of T-Shaped Glulam Beam

Glulam, a sustainable manufactured wood product, is gaining prominence for its numerous advantages. The current study employed an analytical approach using a finite element model developed in ANSYS Workbench 2023 R2 to investigate the flexural properties of glued-laminated timber beams compared to solid T beams. This research focused on assessing the impact of different lamina thicknesses on glulam beams using Larix wood. Glulam beams were categorized into three groups based on lamina thickness: 30 mm, 15 mm, and 10 mm. Additionally, solid T beams were modelled for comparison. Both solid and laminated wood from Larix species were evaluated using ANSYS 23.2. Glued-laminated timber is produced by adhering to graded-sawn timber pieces to fabricate a robust engineered material. This study assesses the flexural properties of T-shaped glued-laminated timber beams and their comparison with solid T-beams.

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.

In-situ characteristic elastic properties of bond-lines in laminated engineered wood products using microscopic digital image correlation

Adhesively laminated engineered wood products (EWPs), such as glue-laminated timber (GLT) and cross-laminated timber (CLT), have gained global popularity due to the increasing development of tall wood buildings. The mechanical performance of a bond-lines is crucial for the structural behavior of EWPs. In this study, a novel method was developed for evaluating in-situ elastic properties of a bond-line in adhesively laminated solid wood products. This method deployed the microscopic digital image correlation (DIC) technique to capture the strain distribution along the bond-line under axial (0°) and off-axis (45°) tensile loading. Three types of adhesives, namely polyurethane (PUR), emulsion polymer isocyanate (EPI), and phenol–resorcinol–formaldehyde (PRF), were used to make specimens. The modulus of elasticity (E) and modulus of shear (G) of a bond-line were accordingly calculated based on the strain along a bond-line and load applied on a specimen. For verification purpose, finite element (FEA) models on CLT and GLT beams were, considering the elastic properties of bond-lines and disregarding the elastic properties, developed to evaluate the effects of the elastic properties of a bond-line on the stress distribution. It was found that the proposed method could be used to accurately determine the in-situ characteristic elastic properties of bond-lines in EWPs. The elastic properties of a bond-line exhibited a large variability, but did not appear to have a significant impact on the overall stress distribution in a specimen. The E and G of bond-lines might be neglected in the structural analysis of large-sized laminated wood products such as GLT and CLT.

Experimental study of hybrid pine-birch glued-laminated timber beams assisted by digital image correlation technique

Experimental study of hybrid pine-birch glued-laminated timber beams assisted by digital image correlation technique

A finite element simulation approach for glued-laminated timber beams using continuum-damage model and sequentially linear analysis

Glued-laminated timber (GLT) is an efficient and renewable material with potential to enhance sustainability in construction, but its potential has been partly hindered by relatively large uncertainty related to its strength. Previous research indicate that by linking information from the grading process to the GLT fabrication more reliable GLT beams could be made. To this end, this paper represents a finite element based modelling approach combining a continuum damage model with sequentially linear analysis that is suitable for simulation of the bending stiffness and strength of GLT beams. The model has been implemented in Matlab and can be easily integrated into different parametric simulation workflows. Based on validation against 36 experimentally tested GLT beams, the model can predict bending stiffness with high accuracy and provides reasonably accurate predictions for bending strength. The model is also capable of producing qualitatively realistic fracture patterns of GLT beams. The mesh-size study suggests that the best agreement for bending strength with test data is obtained with a sparse mesh, which is discussed in detail. The model is considered suitable for follow-up studies involving the optimization of GLT beam layups.

Behaviour of glued-laminated timber beams under impact loading

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

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%.

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.

Development of composite action in a new long-span timber composite floor: Full-scale experiment and analytical approach

The mechanical performance of timber composite floor elements significantly depends on the composite action among different components. The composite action in conventional timber floors with a span limit of 8–9 m has been studied during the last two decades. For long-span timber composite floors with a span over 12 m, how to develop an efficient composite action is still an open question. In this study, the composite action in a long-span timber composite floor system was investigated. The floor system integrates LVL (Laminated Veneer Lumber) panels and GLT (Glued Laminated Timber) beams to form a continuous box girder structure. Various types of inclined screw connections combining LVL and GLT for a composite action were tested. One configuration was chosen to make the 12 m composite floors and four-point bending tests were conducted at different screw spacings. The degree of composite action was evaluated based on the observed overall bending stiffness and relative displacements between different components. The composite action in timber composite floors with concrete topping was also studied. An analytical approach based on Gamma method was adopted to estimate the effective bending stiffness of the composite floor. The findings in this study showed that bending stiffness over 26,000 × 109N·mm2 and composite action over 50 % can be achieved with a small number of screws. Reducing the screw spacing and adding concrete topping would further improve the overall stiffness. The predictions of the analytical model match well with the tested results for both the configurations with and without concrete topping.

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

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

Size effect on bending strength of glued laminated timber predicted by a numerical simulation concept including discrete cracking

The dimensions, particularly the depths, of glued laminated timber (GLT) beams are continuously increasing to realize, e.g., wide-span hall constructions or flexible office buildings. However, experimental investigations of large beams are unavailable because of the tremendous effort involved. Numerical simulation campaigns represent an alternative, but their results are heavily influenced by the modeling strategy, and therefore, a different influence of the beam depths on the bending strength was obtained. To predict this influence, also called size effect, we carried out a simulation program covering 8840 GLT beams ranging from 165 mm to 3300 mm in depth, using advanced modeling concepts including discrete cracking and plasticity.We observed a decreasing characteristic bending strength with increasing beam depths and an almost constant mean modulus of elasticity for both considered strength classes. Additionally, the influence of the beam length on the bending strength is analyzed, and it is shown that this influence can be described reasonably well with a simple analytical model based on Weibull’s strength theory. In conclusion, the effective material behavior of GLT is affected by its dimensions. For large beams, this influence is difficult to obtain experimentally; however, numerical simulation campaigns seem to be a promising way to accomplish this.

Whole life embodied emissions and net-zero emissions potential for a mid-rise office building constructed with mass timber

Increasing global interest in sustainable buildings has generated significant investment in the mass timber industry in recent years. Timber products including Cross-Laminated Timber (CLT) and glue-laminated timber beams (glulam) are a structurally sound, aesthetically pleasing, and potentially carbon reducing alternative to traditional steel or concrete framing. This study uses Life Cycle Analysis methodology to determine the total embodied carbon emissions for a four-story (10033 m2) office building using two design scenarios: a traditional design using structural steel framing and a mass timber alternative utilizing CLT and glulam. The work is founded on detailed material lists for the two building designs that were generated by an architectural contractor with both designs subject to strict evaluation regarding building and construction codes. In addition to a comparative embodied carbon emissions analysis, this study utilized building energy consumption models and existing utility data to estimate operational emissions throughout the lifetime of the building. Energy production with rooftop solar arrays was estimated to evaluate grid emissions avoidance and determine the potential to offset whole life embodied carbon emissions when evaluated over a 30-year time horizon with temporal grid emissions accounting. Three end-of-life scenarios were evaluated for the mass timber products to determine the fate of biogenic carbon stored in the wood biomass. For the three scenarios, different mass fractions were sent to the landfill, directly re-used, or processed into particleboard. Results for the cradle-to-grave embodied carbon emissions analysis show the steel design embodies 3999 t CO2-eq. (398.5 kg CO2-eq m−2) whereas the mass timber design offers an 80–99% reduction in embodied carbon totaling 50–795 t CO2-eq. (5–79 kg CO2-eq m−2) dependent on the end-of-life treatment of mass timber products. Of all the evaluated cradle-to-grave scenarios, the smallest required solar array to fully offset embodied carbon emissions in 30 years was 665 kW with the mass timber building and the end-of-life scenario where 75% of CLT and 95% of glulam were directly re-used with the remaining fractions manufactured into particleboard. Discussion focuses on the challenges and uncertainty in using solar arrays to offset emissions from building construction, operation, and end-of-life treatment, requirements for achieving true net-zero carbon buildings, and methodological limitations.

Behaviour of mass timber members subjected to consecutive blast loads

This paper presents the results of an experimental and analytical investigation into the behaviour of full-scale glued-laminated timber (glulam) beams and cross-laminated timber (CLT) panels subjected to consecutive shock-tube-simulated blast loads. Superficial crack development was observed in the glulam specimens even when loaded within their elastic range. However, these cracks did not appear to affect the overall stiffness and strength of the specimens, as proven through subsequent loading and verification of the experimental resistance curves. Extensive propagation of rolling shear damage was prevalent within the transverse layers of the CLT specimens once flexural failure initiation occurred. Following significant rolling shear damage, the composite nature of the CLT panels were observed to degrade, corresponding to a loss of stiffness and strength. An equivalent single-degree-of-freedom (eSDOF) modelling methodology, capable of taking into consideration the dynamic behaviour of both specimen types and damage accumulation due to subsequent loading, is presented and validated using the experimental test data.

Mechanical and Fire Performance of Innovative Hollow Glue-Laminated Timber Beams.

Fire safety greatly contributes to feeling safe, and it is a key parameter for the selection of building materials. The combustibility of timber is one of the main reasons to have the strict restriction on timber for use as a building material, especially for multistory buildings. Therefore, the main prerequisite for the use of timber in buildings is to ensure adequate fire resistance, using passive and active fire protection measures. This article contains the results of mechanical and fire experimental tests of both normal and innovative hollow glued laminated timber beams. A total of 10 timber beams were tested at ambient temperature, and 3 timber beams in fire conditions, which differed in cross-section type but also in the applied fire protection. The first beam was a normal GL beam without fire protection, the second a hollow beam covered by intumescent paint, while the third was also hollow, additionally protected by mineral wool infill inside the holes. The load-carrying capacity of the hollow beam in ambient conditions was estimated at 65% of the load-carrying capacity of a normal GL beam. Fire tests indicated that hollow timber beams with both intumescent paint and mineral wool infill failed at a similar time as a normal GL beam without fire protection. One-dimensional β0 and notional charring rates βn were obtained. Time to the protective material failure was 17 min. The main cause of failure of hollow beams was the appearance of delamination due to the reduction of the lamella bonding surface.

Seismic performance of glulam timber post and beam structures with and without light frame timber shear wall infill

Timber post and beam structure is typical frame construction with a simple structural system and clear force transmission path. This work studies the seismic performance of glued-laminated timber (glulam) post and beam structures under cyclic loading, as well as the effect of light frame timber shear walls on their seismic performance. Experimental investigation on two types of full-scale glulam post and beam structures was carried out to compare the failure modes, mechanical properties, and energy dissipation. According to the test results, simplified models whose nonlinearity was assumed to be concentrated plasticity in the springs were developed. The comparison between test data and model prediction has a good agreement in terms of evaluation from backbone curves and strength degradation ratio. This calibrated model was then adopted as a benchmark model for further parametric analysis. Eight different configurations considering various aspect ratios were modeled to assess the influence of elastic stiffness and the maximum load-carrying capacity using the pushover analysis. The test investigation and numerical analysis of the glulam post and beam structures with and without light frame timber shear walls help comprehensively understand the seismic performance, providing some valuable guidance for further studies and structural design in engineering practice.

Reinforcement of Timber Beams with Steel Bars: Parametric Analysis Using the Finite Element Method

Incorporating steel bars as reinforcement in glued laminated timber beams is a technique that aims at better structural performance, allowing the reduction of cross-sections. In the present research, based on experimental results from literature about the reinforcement of timbers beams, a parametric study was carried out with the aid of 164 numerical simulations performed within the scope of linear and nonlinear physical analysis via the finite element method to evaluate, with the aid of analysis of variance (ANOVA), the span, base, height, and the reinforcement ratio influence in the service force, ultimate force, and ultimate displacement. Multiple regression models evaluated by ANOVA were established to estimate the service and ultimate forces and ultimate and service displacements as a function of other variables. The results showed an average increase in the service load of 32% and 49%, and the ultimate load of 42.90% and 66.90%, for reinforcement rates of 2% and 4%, respectively. Regarding the multiple regression models, due to the good values obtained from the adjusted determination coefficients to estimate the values of the forces and the ultimate displacements, these can be used in the pre-design of glued laminated timber beams reinforced with steel bars.

Mechanical characterization of homogeneous and hybrid beech-Corsican pine glue-laminated timber beams

This paper describes the results of an experimental investigation on novel homogeneous and hybrid beech-Corsican pine glue-laminated timber (glulam) beams made of short supply chain timber boards and melamine-based adhesive. The aim is to carry out the mechanical characterization of these glulam beams both in the homogeneous and in the hybrid configuration by four-point bending tests with different span to depth ratios of the specimens in order to differentiate bending and shear tests. The experimental results were fitted analytically as well as by means of Finite Element (FE) numerical simulations. Moreover, the stiffness of these novel beams is further evaluated, with respect to a comparison with a commercial product made of GL24h glulam. The experimental and numerical analysis point out the goodness of hardwood for the manufacturing of glulam beams, even in hybrid configuration in which the inner layers are made of low graded timber boards, with a great opportunity to optimize the raw material.

Assessing the structural behaviour of glued-laminated timber beams using distributed strain sensing

Global efforts to reduce the environmental impact of the construction industry have fueled the use of mass timber as a building material. However, the behaviour of mass timber elements is not fully understood, including the effects of localized anomalies (e.g., knots and joints) on global structural performance. To address this need, this study uses distributed fibre optic sensors (DFOS) to better understand the structural behaviour of mass timber elements through the testing of three glued-laminated (glulam) beams instrumented with DFOS under four-point bending. Results of the study demonstrated that DFOS data can be used to identify anomalies (e.g., knots, cracks, and finger joints) in glulam members, capture local strain distributions, and examine the influence of local effects on global structural response. Furthermore, distributed sensing was also found to be an effective tool to measure the in-situ elastic modulus of the timber material.

Assessment of Bending Strength of Afara Glued Laminated Timber using Polyurethane (PUR) Adhesive

Timber has long been a popular building material, with benefits such as low energy consumption and the ability to create an in-built atmosphere that helps to mitigate the effects of global warming. Afara (Terminalia Superba) is a well-known timber species with high demand in Nigeria. The objective of this paper is to assess the physical and mechanical properties of Afara (Terminalia Superba) wood, as well as the flexural strength in flatwise bending of its glued laminated timber beam using polyurethane (PUR) adhesive, to determine its viability for structural construction. The research specimens were made using MS758:2001, EN408, and ASTM D198:2013 standards for the physical and mechanical properties tests. By MS758:2001, a shear test for glue line integrity was conducted to assess the bond performance of the glulam. In the laboratory, bending tests were performed on five glulam beams and five solid beams. Glulam beams were glued together with polyurethane (PUR) adhesive. The bending strength of solid wood was higher than that of glue-laminated wood. Solid Afara (Terminalia Superba) beams have a bending strength of 40.09 N/mm<sup>2</sup>, whereas glued laminated timber has a bending strength of 19.18 N/mm<sup>2</sup>. The preliminary investigation of the timber under BS 5268 (structural use of timber) revealed that glue-laminated beams can be used as structural members in a flatwise orientation, despite their strength being lesser than that of solid beams. Also, the polyurethane adhesive strength has an inverse relationship with the moisture content of the specimens at room temperature.