A reliable determination of the embedment strength and foundation modulus of timber elements is critical for the design and safety assessment of joints in timber structures. However, the existence of various test configurations for characterising the embedding properties of large diameter steel fasteners in timber elements poses challenges in directly comparing and utilising available test data. This paper aims to provide an insight into the influence of embedment property test methods, comparing experimental results from different test setups within the guidelines of the EN 383 and ASTM D 5764-97a standards for European softwood species, Scots pine wood (Pinus sylvestris) and Norway spruce (Picea abies). In addition to the test guidelines, the thickness of the specimen and the application of the load was evaluated within the protocols. A comprehensive statistical analysis was performed to identify statistically significant differences between the groups evaluated. The results of the analysis revealed disagreement between the standards in the evaluation of the strength of the embedding, highlighting the potential bias inserted by the experimental setup and protocol. Furthermore, it was proven that the thickness of the specimens influences both the embedding strength and the foundation modulus of the wood species tested. Finally, no distinctions were observed between tensile and compressive loading within the guidelines of the EN 383 standard.

The lateral behaviour of cross-laminated timber (CLT) shear walls is mainly governed by the non-linear behaviour of connections. Commonly, dowel-type connections that exhibit a ductile force-displacement behaviour are used in the shear angle bracket and hold-down bracket connections. The numerical investigation of CLT shear walls presented herein integrates the so-called Beam-on-Foundation (BoF) model to simulate the ductile connection behaviour in FEM models of shear wall connections and full-scale CLT shear walls. The comparisons of simulation results with experimental data, as well as with engineering design equations and analytical models at the scale of the connection and the shear wall, show reasonable agreement. Due to the integrated BoF model, the shear wall model provides insight into the load distribution between connections, as well as between fasteners within connections and the load distribution over the thickness of the CLT. Despite a need for further investigations, the results of this study highlight the potential of the modelling approach to enhance the understanding of the contribution of the components of the CLT shear wall to its overall structural behaviour. This is indispensable for a safe and reliable design of CLT structures.

This study generalises an upscaling modelling approach, originally proposed for connections loaded parallel to the grain, to account for in-plane multiaxial loading of connections. The main objective is to evaluate how the combination of internal forces affects the brittle response of dowelled connections. A Beam-on-Foundation model is implemented to obtain the nonlinear load-displacement behaviour of single fasteners. Such information is assigned to coupled nonlinear springs located at the connection shear planes in a multiple-fastener connection model to capture the stresses in the timber member between the fasteners. The onset of cracks along the grain direction is evaluated using the mean stress approach. The numerical model shows a strong correlation with prior experimental findings and offers an efficient method for predicting crack initiation in multiple-fastener connections. Additionally, limit curves for the interaction of normal force and bending moment are provided for an exemplary connection layout, considering different slenderness ratios and brittle and ductile failure.

For the design of robust timber buildings, it is essential to develop reliable methods to assess possible brittle failure of connections. Therefore, this paper proposes a three-step modelling approach to predict: (i) the load–displacement behaviour of individual dowels, (ii) the stress distribution in the timber matrix, and (iii) the brittle failure of the timber, in connections with laterally loaded steel dowels. The local nonlinear behaviour of single-dowel connections was determined with a Beam-on-Foundation model and subsequently assigned to nonlinear springs located at the multiple-dowel connection shear planes. The timber member and the steel plate were modelled using 3D shell elements with linear-elastic orthotropic and isotropic material properties, respectively. The interaction between dowels and shell elements was characterised by hard contact and friction. A post-processing module, based on linear elastic fracture mechanics, was implemented to evaluate potential cracks along the grain direction through the mean stress approach. The numerical model aligns well with previous experimental results and provides a novel approach for the prediction of crack initiation based on a realistic load distribution in multiple-dowel connections, while taking advantage of high computational efficiency.

Ductile timber structures are mainly realised using dowel-type connections, which exhibit non-linear force–displacement behaviour that is not directly proportional to the number of fasteners. This so-called group effect has mainly been studied as regards strength, while the group effect in the slip modulus is less investigated. A Beam-on-Foundation (BoF) model for the local behaviour of each fastener is integrated into a multiple fastener steel-to-cross-laminated timber (CLT) connection model, considering CLT layer specific non-linear embedment behaviour. The BoF model for each fastener is kinematically coupled to the surrounding timber matrix, modelled by shell elements with orthotropic linear-elastic material properties. The resulting adaptive connection model is used to predict both shear capacity and slip modulus of steel-to-CLT connections with multiple fasteners and to investigate group effects. A comparison of experimentally-determined and model predicted shear capacity and connection slip modulus showed good agreement. The validated model was applied to study, in addition to the number of fasteners parallel and perpendicular to the outer layer’s fibre direction, the influence of fastener diameter, fastener spacing, loading direction, timber density and steel plate thickness on the load distribution between the fasteners and the overall connection behaviour. The dataset from the parameter study was then exploited to derive a design equation that predicts the group effect in the slip modulus of CLT connections.

This study investigates the possibility of utilizing steel rebars as alternative mechanical fasteners in timber structures. Adopting rebars rather than conventional smooth dowels as fasteners in timber-timber connections might have positive aspects in terms of environmental impact and structural capacity. As to the environmental aspect, it should be mentioned that rebars are typically from two primary sources, namely: a) reused rebar offcuts or b) recycled steel scraps. Regardless of different origins, rebars have reduced environmental impact, especially since rebar offcuts are the primary waste source in concrete construction. As to the strength aspect, which is the main focus of this paper, the authors aimed to check whether enhanced load capacity of dowel-type connections could be achieved due to the higher withdrawal capacity of rebars as compared to smooth dowels. To verify this, tension-shear specimens with either two or four shear planes, adopting smooth dowels or steel rebars as the mechanical fasteners, were experimentally investigated. Plywood with thicknesses of 15 mm or 21 mm was adopted to further verify the contribution from the friction, assuming that thicker plywood generates a higher withdrawal capacity. Analytical models in Eurocode 5 were also adopted to predict the shear plane capacity and the connection stiffness during loading phases. Thereafter, a numerical model was constructed to verify the structural benefits of rebars by adopting different friction models. The model aims to explain experimental observations both quantitively and qualitatively.

In this study, a numerical model that aimed to predict the strength and stiffness, of a single laterally loaded mechanical fastener in steel-to-cross laminated timber (CLT) connections using a Beam-on-Foundation (BoF) model, is presented. The BoF model was used to predict the ductile failure modes of steel-to-CLT connections and considered the layered structure of CLT. When compared to the European Yield Model (EYM), the BoF model was found to be advantageous as it not only predicted the strength but also the stiffness of the connections. A comparison of the slip modulus and strength from BoF model simulations of experimental tests carried out on steel-to-CLT connections showed good agreement with the experimental results. Using the BoF model, the influence of; (i) density, (ii) deck layer orientation, (iii) embedment behaviour, (iv) dowel diameter, (v) steel plate thickness, and (vi) embedment length, on steel-to-CLT connections was investigated in a parameter study. The results presented herein highlight the benefit of the BoF model that considers CLT layer specific embedment behaviour in determining the shear capacity and stiffness of steel-to-CLT connections.

Cross-laminated timber (CLT) has become popular as a construction material and the design of CLT connections is typically based on empirical equations with an average embedment strength of the wood-based product. The experimental study presented herein aims at enhancing the understanding of the relationship between the CLT embedment behaviour and the single layers it is composed of. Non-linear embedment stress–displacement relationships were measured in 244 full-hole and half-hole embedment tests on structural timber boards as well as on CLT produced of parts of the same boards. Three different fasteners, namely a steel dowel with a diameter of 12 mm and the threaded part of screws with a nominal diameter of 6.5 mm and 10 mm, were studied. The design of the experiments allowed to validate a simple mechanical model with parallel springs for the CLT, which showed good agreement with experiments. In addition to a validation of the non-linear spring model, this unique experimental data-set is further exploited in a comparison with empirical equations and for the derivation of a non-linear embedment ratio, between parallel and perpendicular to the grain embedment stresses, over the displacement. Knowledge of the relationship between the non-linear embedment behaviour of the single layers and the CLT element can be further exploited in the engineering design and numerical modelling of CLT connections with dowel-type fasteners. 

Birch plywood has superior mechanical properties compared with plywood made from most softwood species, which makes it suitable for structural application. Plywood is also more environmentally friendly, cost-efficient, and less prefabrication demanding than steel plates. For a proper design of birch plywood as joint plates in timber-timber connections, the embedment behavior of mechanical connectors into plywood needs to be properly investigated. In this study, the authors performed embedment tests of dowel connectors into birch plywood specimens under five different angles from parallel to perpendicular to the face grain with a step size of 22.5 degrees. Dowel connectors with three different diameters were utilized to study the influence of dowel diameter on embedment strength and stiffness. Besides, test series using self-drilling screws and acetylated birch plywood specimens were conducted to study the effect of both fastener type and acetylation. Moreover, full-hole and half -hole test results were compared. The embedment strengths were calculated analytically according to different term definitions. The test results were then compared with the analytical results based on formulas reported in the literature, e.g., Eurocode 5 and other design standards.