Abstract
In this study, dowel displacement-embedment stress relationships for different types, numbers and positions of reinforcements were experimentally investigated using a half-hole embedment test setup. Tests were performed parallel to the grain and in compression. Screws with a full or partial thread at different positions below the dowel and oriented strand board, plywood and nail plates on the loaded surfaces of the specimens, served as reinforcements. Test results underline their potential for an increased ductility of dowel-type connections. Comparison of reinforced and unreinforced specimens suggests premature failure of the unreinforced wood and consequently, an underestimation of the embedment strength as it is subsequently used in the design of dowel connections using the European yield model. This was supported by the investigation of cracks on the surface of the specimens visualized by means of a full-field deformation measurement system. It could be demonstrated that the strength in the embedment test even further increases if the reinforcement elements actively contribute to the load transfer. This property however cannot be considered as embedment strength, but represents the strength of a connection system. Test data is compared to the design equation in Eurocode 5.
Highlights
The embedment behavior of dowel-type fasteners in wood is an important characteristic in the design of timber connections and strongly influences their strength
Comparison of reinforced and unreinforced specimens suggests premature failure of the unreinforced wood and an underestimation of the embedment strength as it is subsequently used in the design of dowel connections using the European yield model
Large displacements are only possible if splitting of the specimen along the grain direction of the wood, due to tensile stresses perpendicular to the grain, is avoided
Summary
The embedment behavior of dowel-type fasteners in wood is an important characteristic in the design of timber connections and strongly influences their strength. The design equation in the European standard for the design of timber structures (EN 1995-1-1 2004) is based on experimental work by Ehlbeck and Werner (1992) and Whale and Smith (1986), as documented for example in Sandhaas et al (2013) The latter discusses embedment characteristics over a broad range of densities and ductility aspects as regards different wood species. A half-hole test setup according to ASTM D5764-97a is applied and corresponding load-displacement characteristics of the reinforced wood specimens loaded parallel to the grain, with dowel displacements up to 30 mm, are studied In this way, the suitability of reinforcements for the testing of embedment properties up to large displacements will be assessed. In general, the ASTM test setup is more prone to splitting and was chosen for the investigation of the effect of reinforcements on embedment properties
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