Timber is becoming an increasingly popular construction material particularly due to its great environmental properties. Just alone around Linnaeus University in Växjö city, dozens of multistory buildings in timber have risen. As the demand for more timber construction is becoming popular, the understanding of timber design must evolve at the same pace. One of the most important parts of timber construction are the connections that hold everything together. One variable that is used to design connections is the embedment behavior. This thesis examined how the embedment behavior of a steel dowel in wood is influenced by moisture content, assembly history, and artificial cracks. In this case the assembly history refers to if the drilling and insertion of the steel dowel was done before or after drying or wetting the specimen. The idea behind the artificial crack was to achieve something similar to a real crack where the crack was created with a precision saw to separate the fibers parallel to the grain. The embedment behavior was studied by means of embedment strength, elastic- and plastic embedment stiffness. In total, 140 embedment experiments were conducted to study the embedment behavior of the dowel in wood. All embedment experiments were carried out parallel to the fiber direction using two species of wood, spruce and birch. Each experimental series had its own attributes to allow a comparison of how the embedment behavior is influenced by moisture content, assembly history, and artificial cracks. The data from the experiments was then used as input to create computer models where the beam on foundation modeling approach was used in conjunction with the finite element computer program Abaqus. A timber-steel-timber connection was modeled to study the influence of the side timber member thickness on the overall strength. The results of the experiments showed that the moisture content and the assembly history can potentially affect the embedment strength and the elastic, and the plastic embedment stiffness. The series that studied the influence of artificial cracks showed that mostly the embedment strength and elastic embedment stiffness are affected by artificial cracks. The numerical simulations indicated that the moisture profile from the experimental data had less influence on the strength for thicker timber side members than it did on thinner. In general, this thesis provides new insights and a better understanding of how the embedment behavior is influenced by moisture content, assembly history, and artificial cracks.

The embedment behavior of dowels in timber structures, as an essential parameter in the design of connections, is the subject of this thesis. There are numerous advantages using timber structures, including sustainability, energy efficiency, and aesthetic appeal. The mechanical performance of connections in timber structures can be affected by environmental variables, such as moisture content. Thus, in the thesis the embedment behavior of dowels in timber, including the embedment strength and elastic and plastic stiffness at various moisture levels was investigated. In addition to different moisture contents, the effects coming along with changing the moisture content, like swelling and shrinkage, in combination with the assembly history were studied. The study investigated the effects of moisture content variations on the embedment behavior of dowels in timber loaded perpendicular to the grain at relative humidity levels of 38%, 65%, and 85% at a temperature of 20◦C. The study also explored the impact of assembly history of the steel dowels on the embedment behavior. The expression ”assembly history” refers the effects of drilling and assembling steel dowels at different times, i.e. if drilling the timber occurs before changing the moisture content or after changing the moisture content.  Full-hole embedment tests were conducted in five different series to cover all three levels of moisture content while taking the assembly history into account. In total, 100 embedment experiments were carried out, with 50 samples of spruce and 50 samples of birch being assessed perpendicular to the grain. In addition, 20 solid timber specimens were exposed to cyclic loading to evaluate the embedment behavior under these conditions. To evaluate the stress on the timber around the dowel, finite-element simulations, using linear-elastic material behavior in combination with volumetric changes due to moisture variation were conducted. Corresponding to the assembly history in the experiments, the situations of moisture variation in presence and absence of the steel dowel for the swelling and shrinkage case were investigated. The experimental results showed that while the elastic and plastic embedment stiffness can be impacted by moisture content only in low MC situations, it can potentially affect embedment strength in both dry and wet conditions. Additionally, the assembly history influences only the plastic stiffness in a low MC condition. Results from cyclic loading have shown no significant difference to embedment strength and stiffness gained from monotonic loading. According to numerical simulations, the tensile normal stress in the direction perpendicular to the load direction is higher than the tension strength for the shrinkage case with the dowel present. This might be explained by using a simple linear elastic material model in the FEM simulation, which causes an overestimation in the stiffness properties. In conclusion, this thesis offers new perspectives and a deeper knowledge of how moisture content, assembly history, and cyclic loading perpendicular to the grain affect the embedment behavior of dowels in timber connections.

Sammanfattning: Wood decay fungi are the main decomposer of lignocellulose material stored in wood. Thus, all factors that affect them could affect their ecological function. This in return, may affect ecosystem functioning in terms of altered carbon emissions from dead wood. Increased temperature is one of the main factors influencing fungal decay. The aim of the current study is to explore the effects of temperature and assembly history (order of species arrival), two important regulators of fungal communities, on wood decomposition. I conducted a microcosm experiment with two temperature treatments and eight assembly histories where each species was allowed to colonize the wood two weeks ahead of the rest of the species. The temperature treatments were set to mimic the effect of climate induced warming. Therefore, I had one treatment with relatively high temperature, representing the expected temperatures year 2100 given the current emission trends of the northern inland of Sweden, and another treatment representing the current normal temperature (1961-1990). The temperature treatments had an average difference of 5°C. In order to see how climate induced warming and fungal assembly history influenced decomposition, I measured and analyzed initial fungal growth, fungal respiration and wood weight loss. Both temperature and assembly history had a significant influence on fungal growth, fungal respiration and wood decomposition. There was also strong interaction between the two factors. The average increase in mass loss under elevated temperature was 19% compared to 14% under normal temperature. The highest mass loss (25%) was when Phlebia centrifuga was the initial species under elevated temperature and the lowest (12%) was when Climacocystis borealis was initial species under normal temperature. All assembly histories had higher mass loss under elevated temperature, but the magnitude varied. For example, when C. borealis was the initial species, mass loss increased by 60% compared to only 7% when Antrodia sinuosa was the initial species. Six out of eight assembly histories had higher CO2 under elevated temperature, with the highest increase (88%) in P. centrifuga histories and the lowest (7%) in C. borealis histories. Even if the results need to be confirmed by field studies, my data illustrates that climate induced warming probably results in higher fungal respiration and deadwood decomposition and that the magnitude of this effect depends on fungal assembly history.