Over 5 million m 3 of engineered wood products (EWPs) are produced in the EU annually and the market is rising. However, EWPs have a high degree of petrochemical use in their manufacturing. In addition, throughout the life span of these EWP products from manufacture to disposal, they emit formaldehyde and other volatile organic compounds (VOCs), which makes recycling very difficult. In this paper, preliminary experimental work on Adhesive Free Engineered Wood Products (AFEWPs) is presented, which covers (1) manufacture of compressed wood (CW) dowels, (2) fabrication of adhesive free laminated beams and connections, (3) structural testing of AFEWPs. Also, the finite element models are being developed to assist designing of AFEWPs in terms of size of compressed wood dowel and dowel patterns in order to maximise their stiffness and load carrying capacities.
An investigation was carried out on CLT panels made from Sitka spruce in order to establish the effect of the thickness of CLT panels on the bending stiffness and strength and the rolling shear. Bending and shear tests on 3-layer and 5-layer panels were performed with loading in the out-of-plane and in-plane directions. ‘Global’ stiffness measurements were found to correlate well with theoretical values. Based on the results, there was a general tendency that both the bending strength and rolling shear decreased with panel thickness. Mean values for rolling shear ranged from 1.0 N/mm2 to 2.0 N/mm2.
To support the transition to a bio-based society, it is preferable to substitute metallic fasteners and adhesives in timber construction with an eco-friendly alternative. Recent studies have identified compressed wood dowels and plates as a possible substitute for metallic fasteners in contemporary and mainstream applications. In this study, a spliced beam-beam connection system using compressed wood dowels and slotted-in compressed wood plates was examined under four-point bending. The study has considered specimens with compressed wood dowels of 10 mm diameter and compressed wood plates of 10 mm thickness. The load carrying capacity of connections using compressed wood dowels and plates were compared to connections utilising steel dowels and plates of equivalent capacity. Typical failure modes, moment resistance and rotational stiffness of both connection systems are evaluated on the basis of the experimental results. Tests have demonstrated similar failure modes when comparing steel-timber and compressed wood-timber connection systems. The mean failure load for the compressed wood-timber connection system is only 20.3% less than that achieved for the steel-timber connection system. The mean rotational stiffness of the compressed wood-timber connection system is 18.55% less than that achieved for the steel-timber connection system. These preliminary results demonstrate the potential for the use of compressed wood elements in the manufacture of timber connections.
The widespread use of energy-intensive metallic connectors and synthetic adhesives in modern timber construction has negative implications for the end-of-life disposal or re-use of the structural timber components. Therefore, it is favourable to substitute metallic connectors and synthetic adhesives with bio-based alternatives such as wood-based connectors. Recent studies have shown that densified or compressed wood (CW) with superior mechanical properties could be suitable for the manufacture of wood-based connectors in the form of CW dowels and CW plates. This study experimentally examines the moment-rotation behaviour of semi-rigid type timber-CW beam-beam connections under pure bending. The study also assesses the suitability of current design rules to predict the moment capacity of timber-CW connections. The comparative study has shown that the moment capacity of the timber-CW connection can be conservatively predicted from the characteristic load-carrying capacity of the connections calculated using the EC 5 strength equations.
Highly loaded and large span timber beams are often used for halls, public buildings or bridges.
Reinforcement of beams may be required to extend the life of the structure, due to deterioration or damage to the material/product or change of use. The paper summarises methods to repair or enhance the structural performance of timber beams. The main materials/products cross sections and geometries used for timber beam are presented. Furthermore, their general failure modes are described and typical retrofitting and reinforcement techniques are given. The techniques include wood to wood replacements, use of mechanical fasteners and additional strengthening materials/products.
In this paper finite element analysis of a five layer cross-laminated timber (CLT) rectangular floor is presented. The model was developed using 3D shell elements with linear elastic orthotropic material properties. Support conditions analysed included fully fixed, semi-rigid and simply supported, and both one and two-way span conditions were considered. For each case, the serviceability deflection was determined from a static small displacement analysis and the first three natural frequencies bending and torsional mode shapes, within a 0-80 Hz range, from mode frequency analysis. The analysis shows that the maximum displacement and frequency response are significantly impacted by the support stiffness and the number of edges supported. These results will contribute to determining the optimum fixing configuration with regard to serviceability limit design (SLD) for various CLT floor geometries.
The objective of this study was to characterise the behaviour of cross laminated timber (CLT) panels and the influence of the panel lay-up on the failure strength. Three different panel configurations of thickness, 60 mm, 100 mm, and 120 mm, were loaded in the out-of-plane direction. The 60 mm and 120 mm panel configuration comprised three layers of equal thickness, and the intermediate 100 mm thick panel comprised five layers of equal thickness. The mean and characteristic bending and rolling shear strength of the panels were examined. The results show that the mean bending and rolling shear strength decrease with the panel thickness. The characteristic results have shown that there is an influence because of the number of boards within the panel. The characteristic bending strength values for the five-layer 100 mm thick panel were found to be higher than that of the three-layer 60 mm panel. The characteristic rolling shear values decreased in the five-layer panels, however, the increased number of layers subjected to the rolling shear results in a reduced variability in the rolling shear strength.
Fibre-reinforced polymers (FRPs) are effective in the flexural stiffening and strengthening of structural members. Such systems can be optimised if accurate numerical models are developed. At present, limited information is available in the literature on numerical models that can predict with good accuracy the nonlinear behaviour of FRP reinforced low-grade glued laminated timber beams. This paper discusses the development of a finite element model, which incorporates nonlinear material modelling and nonlinear geometry to predict the load–deflection behaviour, stiffness, ultimate moment capacity and strain distribution of FRP plate reinforced glued laminated timber beams manufactured from mechanically stress graded spruce. Beams with and without sacrificial laminations are modelled and their performance is compared to unreinforced glued laminated timber beams. The model employed anisotropic plasticity theory for the timber in compression. The failure model used was the maximum stress criterion. Strong agreement was obtained between the predicted behaviour and the associated experimental findings. It was deduced from comparing the results from the numerical model with experimental findings that the FRP plate succeeds in increasing the performance of the adjacent timber significantly. The model is a useful tool for examination of the effect of reinforcement percentage and will be used for optimisation of the hybrid beam.
In recent years, the construction industry has seen a greater focus on the use of sustainable construction materials to reduce the environmental impact of buildings. Timber is one such material that has seen a revival in its use due to its environmental credentials coupled with advances in the manufacture of engineered wood products and connection technologies. While timber and engineered wood products have a high strength-to-weight ratio suitable for large scale construction, timber is an orthotropic material and demonstrates poorer strength when loaded perpendicular to the grain. As a result, special consideration must be given to the design of areas of support where stress perpendicular to the grain develops in timber structures. This paper describes a study which examines the use of densified wood dowels as a sustainable reinforcement against perpendicular to the grain stresses using experimental and numerical approaches. Glued laminated timber samples were reinforced with 2, 4 and 6 densified wood dowels. The experimental results show significant improvements in load-bearing capacity can be achieved. A full 3-dimensional solid finite element model has been implemented in ABAQUS/Explicit software. The numerical model utilises cohesive zone modelling (CZM) and Hill plastic yield criterion to predict the failure behaviour of specimens utilising densified wood dowel reinforcement. The examined numerical modelling approach has been shown to give good predictions of the performance of the dowel-timber interaction and load-bearing capacity of the composite system. The numerical model has been also used in a parametric study to examine the influence of dowel diameter and dowel length on the failure behaviour. A maximum dowel length-to-diameter ratio is recommended based on the numerical results