This paper presents a methodology to characterize the secant shearing stiffness of welding-through wood dowels used in multi-layer spruce beams. Welding-through wood dowel's stiffness behaviour as well as isostatic multi-layer beams' behaviour were investigated experimentally. These elements are made by a specifically designed machine to guarantee repeatability. A model of finite elements was developed to reproduce the bending behaviour of the beams tested from non-linear connection behaviour. This model is then used to study the influence of parameters such as: layer number, spacing of dowels, load type (concentrated or distributed), strength class and beam span. After a sensibility analysis, a parameterized regression model allows to obtain k (ser) and k (u) fastener secant stiffness in compliance with EN 1995-1 standard to design multi-layer beams in an elastic analytical model way. This model is based on the work by Kreuzinger (1999).