Glulam 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.

Experimental investigation on strengthening lap joints subjected to bending in glulam timber beams using CFRP sheets

Abstract Strengthening the carpentry joints is considered a big challenge for designers to maintain the joined timber elements’ load transfer and integrity. This research work investigates different techniques to strengthen the lap joints in glulam timber beams using carbon fiber-reinforced polymer (CFRP) sheets. For this purpose, 12 specimens of glulam timber beams were tested using the four-point loading method. One of the glulam timber specimens was an intact nonlapped specimen, and the others were lapped at mid-span using half-height lap joints. The lap joints were strengthened using different configurations of the CFRP sheets. The test variables were the clamping scheme, bond length, and reinforcement ratio of the CFRP sheets. The analysis of the test results indicates that the CFRP strengthening configuration could be more effective in strengthening the lapped glulam timber beams when the reinforcement ratio of the longitudinal CFRP sheets was equal to 0.303%, and the wrapping CFRP sheets continued beyond the lapped joint by a distance equal to the beam height. Such a strengthening configuration could succeed in increasing the effective stiffness and ultimate load of the lapped timber specimen to 109 and 110%, respectively, relative to those of the intact nonlapped specimen. Moreover, the results reveal that increasing the length or the reinforcement ratio of the longitudinal CFRP sheets without increasing the width of the wrapping CFRP sheets could not succeed in achieving the required improvements in the structural behavior of the lapped timber beams.

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

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

Numerical and Experimental Evaluation of the Mechanical Behavior of FRP-Strengthened Solid and Glulam Timber Beams

Numerical and Experimental Evaluation of the Mechanical Behavior of FRP-Strengthened Solid and Glulam Timber Beams

Investigation of impact behavior of glulam beam strengthened with CFRP

This study’s objective is to examine the general behavior of glulam timber beams strengthened with CFRP (Carbon Fiber Reinforced Polymers) strips and ascertain the impacts of the applied strengthening technique on the performance of timber beams under the influence of rapid dynamic impact loading. In the study, the innovative strengthening method developed with CFRP strips was placed on the lower tensile surface of glulam timber beams and positioned as more than one layer between laminated beam parts. In addition, placing CFRP fan-type anchors on the endpoints of the strips to delay the debonding of CFRP strips from the surface is an innovative application examined in this study that contributes to the literature. The glulam timber beams that strengthened with the developed method and non-strengthened reference test specimens were tested with the free-weight drop test setup. The acceleration, displacement, strain at the tensile surface, and the variations of the applied impact loading by the time were measured and interpreted. In this way, the performance level of the strengthening technique under the effect of the impact loading was investigated. The glulam timber beams strengthened with CFRP strips are modeled using ABAQUS finite element software to compare the numerical analysis with the experimental results and determine the extent to which the numerical analysis might produce realistic results.

Life Cycle Assessment of an Innovative Hybrid Highway Bridge Made of an Aluminum Deck and Glulam Timber Beams

Reinforced concrete and steel are the most commonly used materials in bridge applications in Quebec (Canada). The production of these materials has a significant environmental impact and contributes to the scarcity of non-renewable resources due to the numerous maintenance requirements during the life of the structure. Consequently, there are governmental initiatives and efforts in the province of Quebec to promote the use of aluminum and engineered wood in the construction and rehabilitation of roadway bridges. Those two materials are not widely used due to the short-term vision of decision makers and the lack of technical knowledge for structural uses in highway bridge structures. However, they can be competitive materials due to their local production, durability and recyclability. The life cycle assessment method allows for an analysis of the use of complementary materials, considering all the stages of the life cycle of a structure. The comparison of a roadway bridge made of an aluminum deck on glulam timber beams against a bridge made of an aluminum deck on steel girders shows that, due to the local production and low environmental impact of glulam timber, the aluminum-to-timber bridge is economically and environmentally more advantageous than the aluminum-to-steel bridge. Similarly, a comparison of this alternative aluminum/wood solution to the conventional concrete slab-on-steel girder bridge solution shows a decrease in overall cost by 86% and a decrease in environmental impacts by 88% due to the ease of prefabrication and the relatively low number of interventions over its lifetime.

Verification of the photogrammetric approach on the torsion test method for timber beams

ABSTRACT The photogrammetric approach was proposed in this study to evaluate torsional behaviour of glulam timber beams during the torsion test. The main objectives were to investigate the applicability of the photogrammetric approach and to monitor more details of angles of twist of glulam timber beams. Experiments were conducted and the twists on long and short sides of the cross section were measured using the photogrammetric approach and inclinometer sensors, which were used to validate the accuracy. The test results showed that the optical system allowed monitoring the rotations of the samples at different locations which would not be possible to obtain using the traditional techniques. The results also showed that there is a non-linearity from the measurement of the shear displacements along the long side of the cross-section. However, the average rotation shows clear agreements with the inclinometer readings.

Transformed-section method applied to multispecies glulam timber beams subjected to pure bending

An analytical model, based on the Parallel axis theorem (Steiner theorem) and the procedure of the transformed-section method applied for the evaluation of the elastic moduli of composite timber beams, with different tensile-compressive elastic behavior, is proposed. A comparison between experimental and analytic results has been made on multispecies glulam beams (Pine and Platanus timber), compared with mono-species ones. As well, the work presents the results of a parametric analysis, based on the global modulus and the equivalent moduli in tension and compression.

Photogrammetric evaluation of shear modulus of glulam timber using torsion test method and dual stereo vision system

The shear modulus of timber and timber-based composite materials is a fundamental mechanical property, which is used in the design of timber and engineered wood products. The problem of experimentally determining appropriate values of shear modulus for timber-based composite is not as simple and straightforward as in isotropic materials. Although the torsion test is a recommended standard approach to determine the shear modulus of structural-size timber and glulam beams, it is difficult to measure the rotational deformations of the timber beams. Therefore, in this paper, a stereo camera system combined with a photogrammetric approach is proposed to evaluate the values and variations of the shear modulus of glulam beams under the torsion test. The photogrammetric approach is a non-contact method, which provides an efficient and alternative approach for measuring the deformations of the torsion specimens in three dimensions. A series of experiments was conducted on glulam timber beams under the torsion test to investigate the applicability of the optical approach to evaluate the values and variations of shear modulus as well as to investigate the effect of applying torques in a clockwise or anticlockwise direction on the shear modulus of the beams. This optical system not only allows the performance and reliability of the traditional sensors to be assessed, but also allows the rotational deformation of the torsion samples to be monitored at various locations. This enables the values of shear modulus at different cross-sections of the torsion specimens to be evaluated without the need to use more devices. The test results showed that applying torques to the glulam timber specimens during loading and unloading in either a clockwise or anticlockwise direction does not influence or cause a significant change in the shear modulus of the beams. By comparing shear modulus values of glulam beams measured based on different shear spans, it was found that the larger the shear span the smaller the shear modulus value. This might indicate that the variations of shear modulus values at these different gauge lengths need to be considered.

FE stress analysis and prediction of the pull-out of FRP rods glued into glulam timber

ABSTRACT This paper focuses on the FE analysis of the mechanical behavior of glued composite fiber-reinforced polymer (FRP) rods into glulam timber, using a 3D-continuum damage mechanics. The application of FRP to the glulam timber beams, despite the fact of limited investigations to date, offers an interesting and economic solution for strengthening in timber construction. In particular, the use of glued-in FRP rods for timber connections instead of steel is of great interest, due to the improved durability of the joint systems compared to their equivalent counterparts made of steel rods. For pull-out tests, the estimation of the mechanical response of glued FRP rods into glulam timber is very complex because of the combination of the three different materials: FRP rods, epoxy resin and glulam timber as well as the complexity of the expected brittle modes of failure of the timber. On the other hand, the existing prescriptive approaches (standard design codes) did not cover all the modes of failure expected within timber material and their predictivity is highly depending on the loading direction and on the rod material. There is, therefore, still a need to establish a general and predictive FE model to simulate accurately and cost-effectively the glued-in rod timber connections. In this study, a FE model combining 3D continuum damage mechanics (CDM) and cohesive zone modeling approaches is presented and its effectiveness was verified by comparison to experimental results available in the literature.

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.

Internal reinforcement of laminated duo beams of low-grade timber with GFRP sheets

The purpose of this work is to study the flexural behaviour of Populus×euroamericana I-214 low-grade glulam timber beams, internally reinforced with Glass Fibre Reinforced Polymer (GFRP). To this end, 30 unreinforced beams and 60 reinforced beams, with two ratios of GRFP reinforcement, were produced and tested. Results show an improvement in the flexural behaviour of reinforced beams, with noticeable increases in stiffness (MOE) and ultimate moment capacity (MOR). By using relatively low reinforcement ratios (1.07%, 1.6%) in the tension zone, we have measured an average improvement of 12.1% and 14.7% in stiffness, and an increase up to 23% in moment capacity. GFRP reinforced seems to reduce the influence of timber heterogeneity and singularities (knots, cracks …), which translates into less scattered results and better characteristic values.

FE Modelling of Optimization on Strengthening Glulam Timber Beams by using Compressed Wood Blocks

A new approach to strengthen glulam beams by using compressed wood was introduced by author. Compressed wood (CW) is made of a lower grade wood, which is densified in the radial direction under specific pressure and temperature conditions. In order to optimize the structural performance of glulam beams reinforced by compressed wood, in terms of load carrying capacity, strength and stiffness, parametric studies were carried out on thickness, depth and space of CW blocks. In this study, the dimensions of the beam models were 3800 mm in length, 120 mm in width and 200 mm in depth which comply with the requirements from Eurocode 5, and BS EN 408:2003, where the ratio between the span and the depth equals to 18. There are nineteen beams simulated in the parametric studies using validated FE models. The parameters covered in the simulations include the thickness, depth and spacing of CW blocks, however the CW block width and beam dimensions were remained unchanged. The results indicate that there are significant enhancements on the pre-camber (up to 1/288-deflection/span ratio), initial bending stiffness (up to 23.84%) for a beam reinforced by seven CW blocks with a thickness and depth of 50 mm and 95 mm respectively and ultimate load (increased to 10.4%) of glulam beams reinforced by seven CW blocks with thickness of 40 mm.

Behaviour of hybrid timber beam-to-tubular steel column moment connections

This paper presents an experimental and numerical study into the response of bolted connections between Glulam timber beams and tubular steel columns. Six specimens involving two different connection types subjected to monotonically increasing bending action are examined. The first connection type incorporates top and seat angles blind-bolted to the column and jointed to the beam through long bolts. The second connection type is formed by a steel T-stub slotted into the timber beam and connected to it by means of transverse bolts. In addition, two reinforcing techniques aimed at enhancing the response of the slotted-in T-stub configuration are investigated. These include the provision of a bottom wedge angle between the beam and the column as well as the use of perpendicular-to-grain screws to delay wood splitting. The experimental set-up, connection configurations and material properties are introduced followed by a detailed account of the test results and observations. The main behavioural patterns are identified from the experiments and key response characteristics such as stiffness, capacity and failure mechanism are discussed. This paper shows that the use of bottom wedge angles leads to significant enhancement in the flexural yield strength of the T-stub connections, accompanied by a relatively small change in the location of the bolt-group point of rotation (monitored herein by means of Digital Image Correlation techniques). Besides, the use of reinforcing screws is shown to be an effective detail for substantially increasing the rotational ductility of the connections. Finite element simulations of the tests are also presented, together with a detailed description of the modelling approaches employed, in order to gain further insight into the behaviour of the connections. Finally, the applicability of simplified component-based expressions, which are suitable for practical design assessment procedures, for the estimation of the stiffness and capacity of the proposed hybrid glulam-to-tubular column connections are presented and discussed.

THE FINITE ELEMENT MODELLING OF GLULAM TROPICAL TIMBER BEAM IN BENDING

A full scale bending testing of glued laminated (glulam) timber beam can be costly and time consuming. Therefore, computer modeling is an economical and an efficient tool to achieve the result within the acceptable accuracy. Among other modeling techniques, the finite element modeling (FEM) is widely used for its reliability to simulate and to verify the behaviour of structural elements exactly in the same way the elements perform in the experimental test. Further results of different structural element dimensions or materials can be predicted by modifying the input parameters that are of interest to the study. This study presents the verification of FEM with experimental bending test results on simply supported glulam timber beams made of Keruing and Resak species. The two dimensional (2D) FEM with LUSAS 14.3 software was used. The verification showed an acceptable agreement between the FEM and the experimental results.

Post-tensioning glulam timber beams with basalt FRP tendons

Improvements in the structural performance of glulam timber beams by the inclusion of reinforcing materials can increase both the service performance and ultimate capacity. This paper describes a series of four-point bending tests conducted, under service loads and to failure, on unreinforced, reinforced and post-tensioned glulam timber beams, where the reinforcing tendon used is 12 mm dia. basalt fibre-reinforced polymer. The research is designed to evaluate the benefits offered by including an active reinforcement in contrast to the passive reinforcement typically used within timber strengthening works, in addition to establishing the effect that bonding the reinforcing tendon has on the material's performance. Further experimental tests have also been developed to investigate the long-term implications of this research, with emphasis placed upon creep and loss of post-tensioning; however, this is ongoing and is not presented in this paper. The laboratory investigations establish that the flexural strength and stiffness increase for both the unbonded and bonded post-tensioned timbers compared to the unreinforced and reinforced beams. Timber that is post-tensioned with an unbonded basalt fibre-reinforced polymer tendon shows a flexural strength increase of 2·8% and an increase in stiffness of 8·7%. Post-tensioned beams with a bonded basalt fibre-reinforced polymer tendon show increases in flexural strength and stiffness of 15·4% and 11·5% respectively.

Post-tensioning glulam timber beams with basalt FRP tendons

Post-tensioning glulam timber beams with basalt FRP tendons

Flexural behaviour of glulam timber beams reinforced with FRP cords

Glued laminated timber (glulam) is widely used as a construction material to make up lightweight and large span structures. The basic principle of this material consists in bonding together a number of layers of dimensioned timber with structural adhesives, in order to increase strength and stiffness of the member, and allowing to make up sustainable structures with great visual impact. Recent applications showed the effectiveness of fibre-reinforced polymer (FRP) composites in enhancing the structural performances of glulam beams, with particular reference on their flexural and shear strength. In fact FRP reinforcements could be used to strengthen existing structures or to reduce the dimensions of new structures to be designed. Considering the importance of the latter application, the present work shows the results of four-point bending tests on fifteen small scale glulam specimens, reinforced with glass (GFRP) or carbon (CFRP) cords, varying the kind of adhesive (epoxy resin or melamine glue). Eight further large-scale beams were tested in order to evaluate the role of the scale effect. Finally, an analytical model was developed, able to predict the behaviour of multilayer heterogeneous wood sections and which takes into account the effect of the reinforcements.

Analytical Approach to Predict Pre–Camber Deflection of the Pre-stressed Glulam Beams

A new approach to reinforce glulam timber beams using compressed wood (CW) has been developed by the Author. The compressed wood blocks are inserted into pre-cut holes on the top of glulam beams to produce pre-camber and to generate initial tensile and compressive stresses on the top and on the bottom extreme fiber of the glulam beam, respectively. A simple analytical approach has been developed to predict pre-camber deflections of the beams reinforced with three CW blocks. Assuming that moisture-dependent expansion of the CW block creates an interactive linear pressure between the glulam beam and the CW block, this would generate a pair of eccentric force away from the neutral axis of the beam. It is shown that the pre-camber deflection predicted at midspan of the short beams with various reinforcing arrangements give good agreement with the measured pre-camber from previous experimental results.

Post-tensioning of glulam timber with steel tendons

This paper describes a series of four-point bending tests that were conducted, under service loads and to failure, on unreinforced, reinforced and post-tensioned glulam timber beams, where the reinforcing tendon used was 12mm diameter toughened steel bar. The research was designed to evaluate the benefits offered by including an active reinforcement in contrast to the passive reinforcement typically used within timber strengthening works, in addition to establishing the effect that bonding the reinforcing tendon has on the materials performance.The laboratory investigations established that the flexural strength and stiffness increased for both the reinforced and post-tensioned timbers compared to the unreinforced beams. The flexural strength of the reinforced timber increased by 29.4%, while the stiffness increased by 28.1%. Timber that was post-tensioned with an unbonded steel tendon showed a flexural strength increase of 17.6% and an increase in stiffness of 8.1%. Post-tensioned beams with a bonded steel tendon showed increases in flexural strength and stiffness of 40.1% and 30% respectively.