Finger-jointed Timber Research Articles

Modelling and Multi-Objective Optimisation of Finger Joints: Improving Flexural Performance and Minimising Wood Waste

The wood industry faces the dual requirements of improving the quality of timber products and minimising waste during the manufacturing process. The finger joint, which is an end-to-end joining method for timber boards, is one of the most important aspects of engineering wood products. This study presents a numerical and optimisation investigation of the effects of finger-joint design parameters on the flexural behaviour of finger-jointed timber beams. A numerical model based on advanced three-dimensional finite element analysis was developed to model the behaviour of finger-jointed beams. Using the validated finite element (FE) model and automated parameterisation, a parametric study was conducted to assess the impact of each design parameter of the finger joint, including finger length, tip thickness, and the number of finger joints. The results indicate that the number of fingers and finger length significantly influence the maximum load capacity, while the tip thickness has a marginal effect on performance. This study identifies a design threshold of five fingers and a 14 mm finger length for achieving efficient, high-performance finger-joint designs. In addition, the multi-objective modified firefly algorithm (MOMFA) was proposed to maximise the finger joint resistance while simultaneously minimising the material waste. The optimisation shows that there will be a significant amount of wood waste when using traditional single-objective optimisation that only focuses on structural performance. In contrast, the proposed method achieves comparable load capacity while significantly reducing waste (up to 53.31%) during the joining process. The automated finite element modelling framework and holistic optimisation developed in this study can be used to design and optimise engineering wood products for construction applications.

Structural Properties of Commercial Australian Plantation Hardwood CLT

Significant volumes of plantation hardwood are available in Australia to produce value-added engineered wood products such as cross-laminated timber (CLT). To validate the possibility of utilising this available resource, the bending structural properties of plantation Eucalyptus nitens solid board and finger-jointed feedstock were measured. The studied CLT panels produced from finger-jointed lamellas were subjected to bending strength, bending stiffness, rolling shear strength in bending, and pure rolling shear tests to obtain characteristic design values. Solid and finger-jointed timber test results suggested that boards used in longitudinal lamellas have a bending strength of 36.0 MPa and a modulus of elasticity (MOE) of 13,000 MPa. Finger-jointed timber in crossed lamellas presented a declared bending strength of 25.0 MPa. CLT panels showed a bending strength of 24.0 MPa and a rolling shear strength of 2.0 MPa. The experimental results for the CLT panels evidenced that the CLT bending stiffness matches up very well with the modelled results when an MOE of 13,000 MPa is used to describe the stiffness of longitudinal boards. The results presented in this study establish a basis for the commercial use of Australian plantation hardwood CLT in structural applications such as floors and roofs in commercial and residential buildings.

Assessment of the mixed timber combination effect of finger-jointed timber species using flexural and tensile strength

Off-cut wood is one of the wastes dumped by sawmills, and inadequate length of sawn timber materials fail to fully utilize the wood supply. Finger joint, a method that connects two small pieces of timber, is identified as a sound technique to minimize wastage. Different timber species should be bonded at the finger joint production process for making finger-jointed mixed boards. When mixing the different timber species, timber pieces should be matched based on the mechanical strength. This study was, therefore, conducted to find the strength properties of mixed finger-jointed timber species of wood, namely, Grandis (Eucalyptus grandis), Jack (Aartocarpus heterophyllus), Kumbuk (Terminalia arjuna) and Pine (Pinus caribaea), commonly used in Sri Lanka in the manufacture of furniture. The tests were carried out on timber samples with 19 mm finger lengths made of two sections bonded with an adhesive containing polyvinyl acetate (PVAc). The tensile strength and variation of the flexural strength of the finger length of the samples were studied. BS 373: 1957 was the standard used for the flexural tests. A Universal Testing Machine (UTM 100 PC) was used for the mechanical tests. Timber combination categories are not significantly different for the MOR tests. Pine-Pine vs. Pine-Grandis combination category is significantly different for Bending tests. According to overall results, timber combination categories are significantly different for the tensile tests except for Pine and Kumbuk combinations. The findings of this study will directly benefit the finger joint manufacturers in Sri Lanka.

Identifying the Strength Grade for Finger Jointed Timber Species According to BS 5268-2:2002

Off-cut wood is currently considered as waste thus is dumped by saw mills as they find no means of utilising them. Sawn timber material of furniture factories and short length of sawn timbers are also considered to be wastes in the timber industry. Finger jointing technique which interlock the end joints formed by machining a number of similar tapered symmetrical fingers are recognised in this regards as effective and sustainable means of utilisation of timber wastes. The present study was undertaken to assess the strength grade of finger jointed timber based on BS 5268-2:2002. Seven timber species which are commonly used in Sri Lanka were employed for the assessment with and without finger joints. Values of Modulus of Rupture (MOR), Modulus of Elasticity (MOE), Compression parallel to grain and Compression perpendicular to grain strength of the specimens were measured. Finger jointing was performed with constant geometry (finger length 19 mm, tip width 1 mm and finger pitch 4 mm) using polyvinyl acetate (PVA, P-SWR) adhesive at normal exposure conditions. The strength properties were evaluated by Universal Testing Machine (UTM) according to BS 373:1957. Strength classes relevant to the grade stresses were not significant for finger jointed and clear specimens of Satin, Mahogany, Jack and Grandis. Both clear and finger jointed timber specimens obtained D40 for Satin and Teak, D30 for Jack, Mahogany and Grandis. Teak shows properties similar to both D35 and D40 when used as finger jointed timber. Kumbuk was shown to change from D40 to D30 while using as finger jointed timber. Finger jointed Pine showed stress grade of C22, C24 and C27.

Classification of Finger Joint Timber Based on Strength Index

At present, off-cut wood pieces are dumped by sawmills as they are considered to be wastes in the wood industry. Inadequate length of sawn timber material is also reported to be a limiting factor for fully utilization of timbers. Finger joint, a method which connects two small pieces of timber together is identified as a sound technique to minimize the wastage. As there is no classification system applicable for finger joint timber in Sri Lanka, the present study focused on developing a classification system for selected 32 timber species based on their strength properties. The relationship between the strength properties and density of selected timber species was also investigated. Strength properties of finger jointed timber species were evaluated by three-point bending and compression tests according to BS 373:1957 using Universal Testing Machine (UTM-100).Factors were identified through an analysis to determine the strength index for the selected samples. The strength index values were grouped into five strength classes as very low, low, medium, high and very high. Cluster analysis was used in grouping the species with similar strength properties. Regression analysis was performed to identify the strength index of compression parallel to grain, compression perpendicular to grain, modulus of elasticity and modulus of rupture varies on density. A significant correlation (p=0.05) between the strength index and timber density was observed. Keywords: Finger joint, timber classification, universal testing machine, strengthindex

Experimental and numerical analysis of CFRP-strengthened finger-jointed timber beams

Experimental and finite element (FE) studies of bending behaviour of finger-jointed timber (Spruce) beams reinforced with CFRP material were performed. Four-point bending tests with distinct reinforcement configurations were proposed in order to determine stiffness, ductility and strength values of strengthened finger-jointed timber beams. The experimental results obtained under flexure showed that the external bonding of CFRP increased the load-bearing capacity of finger-jointed Spruce timber beams. The numerical results presented here were based on the Cohesive Zone Model (CZM) available in Abaqus code, allowing the description of the progressive failure mode of the finger-jointed timber beams under flexural load. The FE models took the different material constitutive laws (wood, CFRP and adhesive) into account, including the bond-slip actions between finger-joints and CFRP-timber interface. The results in terms of load-mid span deflection and failure modes obtained experimentally and numerically were compared. Once the FE simulations were calibrated, the differences between experimental and predicted ultimate loads were around 4.5% only. A good agreement was therefore found, proving the relevance of the presented FE models to predict the load-bearing capacity and to capture the failure mode of CFRP-strengthened finger-jointed Spruce timber beams in bending.

Experimental Analysis of the Fire Behavior of Finger-Jointed Timber Members

AbstractFire design models for timber structures usually consider both the loss in cross section attributable to charring and the temperature-dependent reduction of strength and stiffness of the uncharred residual cross section. For bonded timber elements such as glued laminated timber beams, it is assumed that the adhesive in use does not significantly influence the resistance of structural timber beams. To investigate the influence of adhesives in bonded timber elements, a comprehensive research project is currently in progress. The aim of this project is the development of a simplified design model for the fire resistance of bonded structural timber elements, taking into account the behavior of the adhesive at elevated temperature. The paper presents the results of an extensive test series on finger-jointed timber members loaded in tension and exposed to a transient ISO 843 standard fire. The fire tests were performed with different adhesives that fulfill current approval criteria for the use in load-b...