Glulam Timber Research Articles

Joints with bars glued-in softwood laminated timber subjected to climatic cycles

The effect of climatic cycles (extreme temperatures and humidity) on the performance of joints made with threaded steel rods glued by two-component epoxy adhesive in softwood glulam timber is studied. Short-term tests have been made on three types of specimens: standard condition specimens (20°C/65%RH), specimens subjected to extreme temperature and humidity during its storage in climatic chamber in service load situation, and specimens in similar unloaded situation. The load capacity, the failure modes and the load-deflection curves have been compared for the different types of specimens. The obtained results do not show a clear influence of the previous exposition to extreme climatic situations in the strength of the joint. On the contrary, the stiffness of the joints, especially those with longer anchorage length, has been reduced up to 35% in the specimens that were previously subjected to climatic changes, both unloaded and in load service situation.

Technical Guidance Note (Level 2, No. 14): Design of unrestrained timber beams

This Technical Guidance Note addresses the design of timber elements that are unrestrained against lateral torsional buckling. It explains how such beams are analysed and designed. The impact of notching the supports of beams is also considered with respect to the shear capacity of the beam. For clarity and brevity, this note only covers solid and glued laminated (glulam) timber elements; compound and composite beams, such as flitch beams, are not considered. The connections within timber frame assemblies will be addressed in a future note. Readers should also be aware that this note forms part of a trio of Technical Guidance Notes leading to the design of bespoke timber trusses – assemblies made from unrestrained timber beams and posts. Notes on the design of timber posts and bespoke timber trusses will follow later in the series.

Bonding performance of CCA treated glulam timber under different environmental exposure

Bonding performance of CCA treated glulam timber under different environmental exposure

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.

Shaking table testing of post-tensioned timber frame building with passive energy dissipation systems

A recently developed technology for the construction of multi-storey timber buildings called Pres-Lam uses long lengths of prefabricated laminated timber connected together using pre-stressing steel tendons or bars. A 3-dimensional, 3-storey, 2/3rd scaled Pres-Lam frame building was tested on the shaking table of the structural laboratory of the University of Basilicata. The main objectives of this study were: (1) to confirm the effectiveness of the Pres-Lam technology, originally developed using laminated veneer lumber, for glue laminated (Glulam) timber structures and (2) to validate the current modelling approach in predicting the dynamic response. This paper describes the design, detailing and construction of the experimental model followed by explanation of the testing programme. Two sessions of testing were performed considering different column-base conditions, both with and without the activation of externally mounted dissipative steel angles. The test results are compared with numerical predictions obtained through nonlinear analysis. These numerical models are shown to provide an accurate representation of the dynamic response.

Cradle-to-Gate Life-Cycle Impact Analysis of Glued-Laminated (Glulam) Timber: Environmental Impacts from Glulam Produced in the US Pacific Northwest and Southeast*

Abstract This study was an update on the 2000 life-cycle inventory data on material and energy inputs associated with the production of 1 m3 of glued-laminated (glulam) timbers produced in the Pacific Northwest (PNW) and the Southeast (SE) regions of the United States. This article looks at the cradle to gate for the entire glulam production processes, which include forest harvest, lamstock production, and glulam beam production. Data collected from glulam beam manufacturers in 2013 allowed for the development of a life-cycle assessment utilizing the product category rules for North American Structural and Architectural Wood Products so that the results from these analyses can be used for the development of environmental product declarations of glulam beams produced in the United States. Comparing the results of this study with the life-cycle assessment based on the 2000 survey data shows 30 percent reductions in global warming potential of glulam beams produced in both the PNW and the SE and reductions in the use of energy derived from fossil fuels by 40 percent in the PNW and SE. The overall net carbon sequestered in 1 m3 of PNW glulam is equivalent to 938 kg of CO2 and 1,038 kg of CO2 in the SE. Utilizing techniques that reduced the use of electricity and minimizing the transportation distances of the raw materials and resins to the mill could help to further reduce the carbon footprint of the glulam beam manufacturing process.

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.

Behavior of Glulam Columns Reinforced by Near-Surface-Mounted CFRP Laminates under Eccentric Compression Loading

This paper introduces simple glued laminated (glulam) timber columns reinforced by near-surface-mounted carbon-fiber-reinforced polymer (CFRP) laminates (GTMC columns). Twenty-four columns were fabricated and tested under eccentric compression loading to validate the effectiveness of this kind of column. In accordance with the degrees of eccentricity, specimens were divided into three groups. In each group, one column without inlaid CFRP laminates served as a control column, while the others were inlaid with CFRP laminates. All columns were tested for ultimate load capacity, displacement ductility, failure mode, and energy dissipation capacity. Test results show that inlaid CFRP laminates are effective in increasing ultimate load capacity and deformability. Meanwhile, the corresponding analytical model was also derived to predict the ultimate load capacity of GTMC columns. A comparison of the predicted and tested ultimate load capacities demonstrated that the analytical model is generally able to evaluate the ultimate load capacity of GTMC columns with an average underestimation of 8.7%. Furthermore, a finite-element analysis was conducted to investigate the effects of thickness and mounted depth of CFRP laminates on ultimate load capacity and initial stiffness.

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.

ASSESSMENT IN BENDING AND SHEAR STRENGTH OF GLUED LAMINATED TIMBER USING SELECTED MALAYSIAN TROPICAL HARDWOOD AS ALTERNATIVE TO TIMBER RAILWAY SLEEPERS

This paper presents a pilot study on bending and shear strength of glued laminated (glulam) timber using selected tropical timber namely, Kekatong (Cynometra spp.) and Melagangai (Potoxylon melagangai) as an alternative for timber railway sleepers. Selected timbers were manufactured in accordance with MS758:2001 and the bending test was conducted according to ASTM D198:2013. The shear test for glue line integrity was performed to observe the bond performance in glulam accordance to MS758:2001.The results showed both species can be used as structural members since the bending strength obtained from the laboratory work is greater than the allowable bending strength. In terms of the percentage of wood failure, the bonding characteristics of both glulam satisfied the bonding requirement stipulated in the standard and have the potential to be used as glulam timber railway sleepers.

COMPRESSION STRENGTH OF COMPOSITE GLULAM TIMBER REINFORCED BETWEEN FIRST AND SECOND, THIRD AND FOURTH LAMINA

The use of GFRP sheet as reinforcement in Mengkulang glulam timber is considered to be particularly promising, since the durability of Mengkulang glulam is improved and the application is easier and faster due to lightweight properties of GFRP. Fiber reinforced polymers incorporated with glulam provide significant gains in strength and stiffness, as well as modify the rupture mode of these structural elements. In this study, compression test was carried out on two types of specimen, reinforced and unreinforced Mengkulang glulam block. Size of Mengkulang glulam block is 120 mm x 120 mm x 120 mm. For reinforced glulam block, GFRP sheet was placed between the first and second layer, third and fourth layer of lamina. The compression load was applied perpendicularly to the timber grain. Compression test is carried out using Universal Testing Machine (UTM 1000kN). Consequently it has been noted that by layering GFRP sheet between lamina could increase the compression strength of glulam to resist load. Significant differences between unreinforced and reinforced specimens are 12.6 percent. The highest average compressive strength of reinforced and unreinforced glulam is 11154.05 kN/m2 and 9808.75 kN/m2 respectively.

PULL OUT STRENGTH FOR DIFFERENT SIZE OF DOWEL AND GRAIN DIRECTION OF GLULAM

This paper presents an experimental program for testing glued-in dowel glulam timber joints. Hundred thirty glulam specimens, each with a single glued-in rebar parallel to the grain and perpendicular to grain with different size of dowels 12mm, 16mm and 20mm were tested to evaluate the effects of anchorage length and different dowel diameter for parallel and perpendicular to the grain on pull-out strength and bond behaviour of glued-in rebar timber joints. The test results showed that the maximum load for specimen with dowel glued-in parallel to the grain given the higher maximum load than dowel glued-in perpendicular to the grain direction. Failure modes were characterized by pull out failure in the mode of adhesive-dowel, yet one sample failed in timber-adhesive mode. This might happened because the surface of the timber was burned by drilling machine during the drilling process. The pull-out was tested with different thickness grain direction with different dowel size with a rate of 2mm/min and the failure modes were observed after the testing of pull-out test. PRF is the adhesive used for the strengthening purposes. Resistance to the withdrawal of dowels glued-in perpendicularly was 44.2% to 53.5 % lower than that obtained for dowels glued-in parallel to the grain direction. The result shows that the dowel glued-in parallel to the grain given the higher maximum load than dowel glued-in perpendicular to the grain direction.

Mechanical performance of glued-laminated timber beams symmetrically reinforced with steel bars

The technology of glued laminated (glulam) timber has enabled the design of composite structures with large dimensions. The laminations are generally derived from the sawing of small trees and species of rapidly growing, which yields laminates with low mechanical properties. This study evaluates the benefits of the reinforcement of glulam beams, by employment of steel reinforcement ratios of 2% and 4%. In the beams with a ratio of reinforcement of 2%, in relation to the unreinforced glulam beams, the stiffness increased approximately 52% and the serviceability load increased 53.1%, and with the employment of steel ratio equal to 4% these increases were in the order of 73% and 79.2%, respectively. The results showed that the insertion of steel bars can reduce the inherent variability of wood and increase significantly the stiffness of glulam, which consequently increases the beam capability for serviceability limit states.

Cyclic behaviour of glulam shear walls with bolted connections

Dowels and bolts are well established types of fasteners for timber connections. They are fast and easy to assemble which made them become a common solution for joining heavy timber elements. This study investigates the feasibility of bolted connections as a possible anchoring solution for heavy shear walls under seismic loads. Fully reversed cyclic tests were performed on glued laminated (glulam) timber shear walls with un-reinforced and reinforced bolted connections. This study builds up on a previous research conducted on single bolted connections tested under quasi-static tensile loading. Testing an entire wall provides additional information on the performance of the connections under the actual load distribution (tensile and shear force) due to horizontal load which varies the shear force distribution in the fasteners compared to the case of a simple connection tested in tension. The influence of the fastener spacing and distance from the loaded and unloaded edge on the failure mechanism was investigated, as well as the effect of the reinforcement on the cyclic response of the connection in comparison to the unreinforced solution. The experimental study proved that conventional bolted connections are a feasible solution for anchoring shear walls to the foundation. Reinforcing the connection area with self-tapping screws resulted in reduced splitting, increased connection ductility and increased equivalent damping. However, bolted connections experience significant irreversible damage, namely plasticization of the bolts and timber crushing at the interface with the bolt, at the end of the seismic event.

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.

FRP reinforcement of low-grade glulam timber bonded with wood adhesive

The commercial development of composite reinforced timber beams manufactured using low-grade laminated wood would be considerably enhanced if the same adhesive was permitted to be used both at the wood–wood bond interfaces as well as the FRP plate–wood bond interface. This paper describes a programme of tests undertaken to assess the structural performance of low-grade glued laminated timber reinforced with glass fibre reinforced plate (GFRP) bonded using the conventional wood laminating adhesive, phenol resorcinol formaldehyde (PRF). The use of a practical reinforcement percentage of 1.86% of the cross-sectional area resulted in a moderate stiffness enhancement of 18% and considerable improvements in the ultimate moment capacity of 31%. Strain profiles demonstrated that utilisation of the compressive behaviour of the timber was improved in the reinforced beams. Most importantly, at no stage during testing of any of the reinforced beams was the quality of the FRP–wood bond compromised. The results from a nonlinear finite element model showed excellent agreement with the experimentally determined ductile load–deflection behaviour of the reinforced beams. Furthermore, satisfactory comparisons are obtained between the predicted and measured failure loads and strain profile behaviour. Slip at the FRP–wood interface, bonded using a wood laminating adhesive, was considered negligible. The research proposes an improved alternative whereby the same adhesive is permitted to be used for all bond interfaces in the reinforced beam and the use of more expensive epoxy adhesives at the FRP–wood bond interface is avoided.

The Reduced Cross Section Method Applied to Glulam Timber Exposed to Non-standard Fire Curves

Timber is an desired material for structural applications due to its green credentials and attractive external appearance. Fire safety design of timber structures is largely limited to considering the exposure of elements to the standard fire, to which timber demonstrates exceptional resilience. This paper reports on a series of tests which were carried out with the intention of exploring the impact of non-standard fires on timber elements. Because of the natural variation in timber elements, the tests and the resulting analysis of the test results were conceived and designed in such a way that as much information about the statistical distribution of the response of the elements as possible could be obtained. The resulting testing programme comprised four furnace fire tests, each of eight loaded timber beams, with three different temperature time curves: two standard fire tests, one long-cool parametric fire and one short-hot parametric fire. The reduced cross section method for structural calculations is extended in this paper to parametric fire exposures, and the results of the tests are compared with this method. It is shown that the thickness of the zero-strength layer is dependent on the temperature time curve to which the timber is exposed in the furnace and that the 7 mm zero-strength layer prescribed in EN 1995-1-2 may be un-conservative for members in bending. For the cases studied, the zero-strength layer thickness in bending is shown to be around about 15 mm under standard fire exposure and 16 mm under exposure to a long cool parametric fire. Conversely, the zero-strength layer is only 8 mm deep under exposure to a short hot parametric fire. This has implications for the design of timber elements not only for parametric fire exposure in enclosures, but also perhaps for the use of timber elements in large open structures such as halls or arenas where more localised fire exposure or travelling fire exposure may be expected.