This report represents the results of the activities performed in working group 1, Basis of Design. The most important task of working group 1 was the defragmentation and harmonization of techniques and methods that are necessary to prove the reliable, safe and economic application of timber materials or products in the construction industry.
This report is structured into five parts. At first general principles regarding the design formats are addressed (Part I). Afterwords timber specific aspects regarding code calibration (Part II) and serviceability (Part III) are summarized. In Part IV other demanding issues for the implementation into Eurocode 5 are addressed. Here also summaries of joint activities with other working groups on cross laminated timber and timber connections are presented. The report concludes with a guideline for data analysis (Part V).
The aim of the experimental study presented herein is the assessment and quantification of the behavior of individual dowels in multi-dowel connections loaded by a bending moment. For this purpose, doubleshear, steel-to-timber connections with nine steel dowels arranged in different patterns and with different dowel diameters were tested in 4-point bending. In order to achieve a ductile behavior with up to 7° relative rotation, the connections were partly reinforced with self-tapping screws. The reinforcement did not influence the global load-deformation behavior, neither for dowel diameters of 12 mm nor for 20 mm, as long as cracking was not decisive. The deformation of the individual dowels was studied by means of a non-contact deformation measurement system. Thus, the crushing deformation, i.e. the deformation at the steel plate, and the bending deformation of the dowels could be quantified. In case of 12 mm dowels, the bending deformation was larger than the crushing deformation, while it was smaller in case of 20 mm dowels. Moreover, dowels loaded parallel to the grain showed larger bending deformations than dowels loaded perpendicular to the grain. This indicates that the loading of the individual dowels in the connection differs, depending on their location.
The load distribution in multi-dowel timber connections under bending moments was investigated by means of an integrative evaluation of a hierarchically organized test program, which encompassed component tests as well as single-dowel and multi-dowel connection tests. It was demonstrated that the anisotropic material behaviour of Laminated Veneer Lumber, and consequently of wood in general, leads to a non-uniform load distribution among the dowels, even for multi-dowel connections with a circular arrangement of dowels. Model predictions from this study highlight inefficiencies of the simplified calculation approach, based on the polar moment of inertia, i.e., based on isotropic theory. Loads of dowels loaded parallel to the grain were found to be underestimated by up to 50%. Through the hierarchically organized experimental campaign with full-field deformation measurement techniques, load distribution effects could be related to the orthotropic material behaviour of wood expressed in terms of load-to-grain angle dependent slip curves of single-dowel connections.
