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4.4 DOWEL-TYPE FASTENERS LOADED
PERPENDICULAR TO GRAIN
22-7-2 J Ehlbeck, R Görlacher, H Werner
Determination of perpendicular-to-grain tensile stresses in joints with
dowel-type fasteners – A draft proposal for design rules
Introduction
Joints with dowel-type fasteners loaded at an angle to the grain direction
of the wood cause in addition to the embedding stresses considerable local
perpendicular-to-grain stresses next to the fasteners. These stresses may
under certain conditions lead to failure at a load level lower than the loadcarrying
capacities of the fasteners themselves.
A simplified method to take into account these stresses is given in the
CIB-Code and was also provisionally accepted in the draft Eurocode 5.
This design method is, however, unsatisfactory and can lead to uncertainties,
e.g. for single loads applied to glulam beams and acting perpendicular
to the grain direction. This simplified method does not sufficiently take into
account:
– the joint's geometry;
– the number of fasteners in the joint;
– the distribution of the fasteners over the beam depth;
– the perpendicular-to-grain tensile strength of the wood in relation to the
actually stressed volume;
– the ratio between the distance ar of the furthest row of fasteners from
the loaded beam edge and the beam depth h;
– the range of the area stressed by the perpendicular-to-grain acting load.
Based on tests and theoretical reflections performed at the University of
Karlsruhe during the last decade a design procedure for joints with doweltype
fasteners is evaluated and presented for discussion.
32-7-3 M Yasumura, L Daudeville
Design and analysis of bolted timber joints under lateral force perpendicular
to grain
Introduction
The fracture of wood is one of the major causes of brittle failure in timber
structures. It brings serious damages of timber structures under seismic action
by reducing the energy dissipation. Fracture of wood occurs frequently
at the joints subjected to the force perpendicular to the wood grain. This
failure is not always predictable because the design of timber joints is generally
based on the yield theory that does not include the failure of joints
due to the fracture of wood. The fracture mechanics is one of the most effective
methods to analyze the fracture of timber structures. It is particularly
useful for estimating the maximum strength of the joints when the crack
propagation is stable. In Paper 29-7-8, the fracture of a single bolted joint
subjected to a lateral force perpendicular to the grain was analyzed by
means of the ASM (Average Stress Method) and the LEFM (Linear Elastic
Fracture Mechanics). It showed that the ASM and the LEFM were appropriate
tools to predict the crack initiation and propagation of the bolted
timber joints subjected to lateral force perpendicular to the grain, respectively.
In this study, the load carrying capacities of a single and multiple
bolted joints obtained from the lateral loading tests were compared with
the results of simulation by means of the LEFM and yield strength.
Conclusions
It was found that the load carrying capacity obtained from the simulation
by means of the LEFM agreed very well with the experimental results, and
the LEFM was the appropriate tool to estimate the failure of bolted timber
joints. It was also found that the load carrying capacity of the joints subjected
to lateral force perpendicular to the grain was mostly smaller than
the yield strength, and they failed due to the fracture of the wood before
the yielding of bolts. Special consideration should be done on design of
joints subjected to the lateral force perpendicular to the grain.
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.31