Timber joints featuring glued-in rods (GiR), comprising a combination of a rod, adhesive (glue), and timber, play a crucial role in the mass timber construction industry. The reliable and efficient design of GiR joints is essential for the success of large-scale timber-based structural systems. However, the intricate mechanical complexities inherent in the load-displacement behavior of timber and adhesive joints pose significant challenges in accurately analyzing and designing GiR connections.

This contribution aims to employ the theory of elasticity to establish an analytical procedure for evaluating the stiffness and loading capacity of GiR joints under various loading configurations. The proposed analytical model allows for treating the adherents as isotropic, orthotropic, or multilayer composite materials.

The accuracy of the proposed analytical model is assessed by comparing it with laboratory test data and Volkersen's model, providing valuable insights for the efficient design of timber connections involving GiR.

The design of robust timber buildings requires reliable methods for assessing possible failures of connections that can have serious consequences. This contribution proposes a three-step modelling approach to predict: (i) the ductile load-displacement behaviour of individual fasteners, (ii) the stress distribution in the timber matrix, and (iii) the brittle failure of the timber in laterally loaded connections with steel fasteners and slotted-in steel plates. The local nonlinear behaviour of single dowel-type fasteners was determined utilising a beam-on-foundation approach, which subsequently was used to define nonlinear springs located at the fastener’s shear plane in a multiple fastener connection model to obtain the stress distribution in the timber matrix. 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 rigid cylinders, representing the fasteners, and the 3D shell elements, representing the timber and steel members, was characterized by defining hard contact in the normal direction and friction in the tangential direction. A Python-scripted post-processing module, based on linear elastic fracture mechanics, evaluated potential brittle failure through the mean stress approach. The stress distribution was obtained for each load increment during numerical analysis and used to calculate the mean stress length for various potential failure paths along the grain direction. The failure criteria were assessed for each pre-defined path and load increment to identify the critical path and estimate the connection’s load-carrying capacity. The numerical model accurately fitted previous experimental tests regarding load-carrying capacity and connection slip, providing realistic load distribution in multiple fastener connections and accurate predictions of crack initiation, while taking advantage of high computational efficiency.

Due to high localised shear and perpendicular to the grain tensile stress concentration, timber in dowel-type connections may fail before the ductile connection capacity is reached. Experimental studies have found that even if timber connections are designed to avoid brittle failure in accordance with international standards, they still may exhibit brittle failures. In response, the scientific community has endeavoured to develop more accurate and reliable design models to predict the brittle load-carrying capacity, and suitable for engineering applications in a straightforward way. For connections with stock fasteners, embedment stresses are practically uniform across the thickness of the timber member, allowing to activate the entire timber member for the connection load transfer. However, in connections with slender fasteners prone to bending, and therefore, promoting ductility, the embedment stresses can vary significantly across the member thickness. Thus, it is essential to assess the length which effectively contributes to the connection's load-carrying capacity. This length can be defined by the so-called “effective thickness” of the timber member. Various models are available in the literature for estimating the effective thickness of timber based on the bending deformation of the fasteners. These models primarily differ in the theoretical definition of the effective thickness and do not consider the non-linear connection behaviour. In this context, the main objective of this contribution is to establish a mechanical understanding of the effective thickness of timber used in the design of dowel-type connections. This is achieved by drawing insights from a numerical non-linear beam-on-foundation model, and comparison of results with analytical formulations presented in international standards and the literature. In addition to the model validation, a parametric study is presented considering timber-to-steel connections with single, double, and multiple shear planes. Various parameters such as plate thicknesses, fastener slenderness ratios, and material properties are varied for a comprehensive comparison with other models.

The recent trend towards taller timber buildings gives robustness requirements a more prominent role. These buildings must be able to resist initial damage from accidental events (e.g., the loss of a column) without disproportionate consequences. In recent years, several examples of partial or full building collapse have occurred due to, e.g., renovation works or explosions. The collapse of a structural member often results in dynamic loading that imposes high strain rates and vibrations. Dowelled steel-to-timber connections are commonly used in practice, but the influence of cyclic and high strain rate loading on their structural behaviour is not yet well understood.

Steel-to-timber connections with a slotted-in steel plate and a single laterally-loaded dowel were tested under high strain rate monotonic loading and quasi-static cyclic loading. The experiments were performed on LVL Kerto-S connected by S235 dowels with a diameter of 10 mm, and comprised four different load-to-grain angles between 0° and 90°. Five different strain rates were investigated between 0.05 mm/s (quasi-static) and 150 mm/s.

First analyses of the experimental data for high strain rates (150 mm/s) and load-to-grain angles of 0° revealed a minor increase in mean maximum force by 4% and a significant decrease in ductility by 46%, compared to the quasi-static reference case. For load-to-grain angles of 90°, the increase in mean maximum force was 11% with negligible changes in ductility. In both cases, the failure mode remained ductile with three hinges forming in the dowels, even though less pronounced for high strain rates. For 0° load-to-grain angle, splitting within the timber side members was observed after extensive deformation of the dowels.

In the cyclic tests, failure occurred through rupture of the dowel after reaching the cycles with four to eight times the yield displacement. The hysteresis loops showed pinching as well as strength and stiffness degradation.

Beam-on-Foundation (BOF) models were mainly applied to represent the mechanical behaviour of timber connections with laterally loaded dowel-type fasteners under monotonic loading. Modelling of such connections under cyclic loading, applying BOF-models, is however less investigated. The aim of this study is to contribute to a better prediction of the global hysteretic behaviour, the load distribution along the fastener, and potential fatigue failure in the steel fastener of timber-to-steel connections with a single dowel-type fastener under large cyclic loads.

This was achieved through the extension of an existing monotonic BOF-model and its conversion into a quasi-static simulation using Abaqus Explicit R2022x. In the BOF-model, the fastener is represented by linear Timoshenko beam elements with a linear-elastic nonlinear-plastic material behaviour. Spring elements, defined by uniaxial connector elements in Abaqus, represent the embedment behaviour of steel and timber. For steel, a linear-elastic and for timber, a nonlinear-elastic-plastic embedment behaviour, using the Richard-Abbott function, was implemented. A parameterised unloading behaviour was added to the connector definition using an inverted Richard-Abbott function. For both, loading and unloading behaviour, the function depends on the properties of the timber material and the load-to-grain angle. To account for a different unloading behaviour at different displacement levels, an additional dependency on the displacement at the start of the unloading phase was incorporated. Cyclic embedment tests of dowels in spruce were conducted to generate input properties for the connector elements of the BOF-model.

For validation of the connection model, quasi-static cyclic tests were carried out on timber-to-steel connections with one dowel. Good overall agreement was found between simulation results and the experiments with respect to the global hysteresis shape and dissipated energy. Strength and stiffness properties were especially well predicted for the initial loading phase, while the unloading stiffnesses showed larger deviations.