Elementary and advanced modelling of the splitting strength of timber connections

J.C.M. Schoenmakers
Eindhoven University of Technology, the Netherlands

The load-bearing capacity of a timber member loaded perpendicular-to-grain by a connection is governed by either the embedment strength, the bending yield strength of the steel fasteners, or the splitting strength of the timber. Only coarse models for predicting the splitting strength are implemented in structural design codes, if any. It is of great importance for engineers to avoid splitting failure because it is often a brittle failure mode.
This paper presents an overview of analytical, numerical and experimental research on the splitting strength of timber connections loaded perpendicular-to-grain by mechanical connections, conducted at Eindhoven University of Technology.
Based on the theory of Fracture Mechanics, an analytical expression for predicting the splitting strength is derived. This analytical expression is applied to members loaded by a single connection composed of dowel-type fasteners such as nails, dowels and bolts. The expression is calibrated with experimental results, after which its prediction ability is verified using another set of experimental data. For this purpose, performed experiments as well as results presented in literature are used. To confirm the physical behaviour predicted by the analytical expression, a numerical study is performed based on linear and non-linear fracture mechanical finite element models. From this it follows that the energy associated with fracture of connections perpendicular-to-grain is close to the mode I fracture energy. Amongst others, the number of fasteners and the loaded edge distance of the furthest row of fasteners are significant parameters.

Key words: Timber, fracture mechanics, connections, equilibrium state, splitting strength