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– shear failure of a group of rows
To avoid the shear failure in one row the dowel strength and the spacing of
the dowels has to be adapted to the shear strength of the timber.
A failure of a group of rows is possible by inadequate placing of the
dowels. By applying a concentrated force parallel to grain only little distribution
perpendicular to the grain direction is possible, due to the nonisotropic
properties of timber. Therefore a reduced effective width has to
be considered if the fasteners are not well distributed over the whole width
of the timber.
31-7-6 A Jorissen, H J Blass
The fastener yield strength in bending
Introduction
The strength of single fastener connections with dowel type fasteners is, in
Europe, determined according to the Yield Model, first presented by K.W.
Johansen (1949). The fastener's yield capacity and the embedment strength
are both governing material properties.
The fastener's yield capacity in bending is often determined according
to prEN 409 (1994). Although the method, described in this standard, is
meant for nails with a diameter < 8 mm, it is also used for other dowel
type fasteners, e.g. bolts. It is discussed whether using this method for diameters
> 8 mm are recommendable or not.
Summary and conclusion
In this paper the determination of the fasteners yield strength in bending
for large diameter dowel type fasteners is discussed. ENV 1995-1-1 requires
a tension test. A bending test for small diameters, (nails) is described
in 409, which is also frequently used for large diameters.
Since dowel type fasteners are loaded in bending, a bending test prevails
for large diameter dowels also. However, since the bending angle required
in EN 409 (= 45º) is never reached for large diameters, this required
angle should be reduced (e.g. 10°).
The factor 0.8 in the equations given in Eurocode 5 seems to reflect
bending angles reached at failure load reasonable well.
32-7-1 M Mohammad, J H P Quenneville
Behaviour of wood-steel-wood bolted glulam connections
Abstract
This paper details verifications tests carried out at the Royal Military College
of Canada (RMC) on wood-steel-wood bolted glulam connections.
Twelve groups of specimens were tested. Specimens configurations were
selected in such a way to include fundamental cases. Comparisons between
experimental results and predictions from proposed equations for
wood-steel-wood and wood-steel bolted connections are given. Proposed
design equations were found to provide better predictions of the ultimate
loads than current design procedure especially for bearing. However, row
shear-out predictions seem to over-estimate the shear strength. Adjustment
may need to be made to the proposed equations for row shear-out by introducing
the effective thickness concept instead of using the full member
thickness. Better predictions for row shear-out were achieved using the effective
thickness instead of the full thickness. The research program is described
in this paper along with results and proposed design equations for
wood-steel-wood bolted connections.
Conclusions
Based on the validation tests of the proposed design equations for woodsteel-wood
bolted connections, it can be concluded that:
5. Current Canadian design code (086.1-94) leads to over-designed woodsteel-wood
bolted glulam connections, especially with multiple bolts,
where it under-estimates the failure loads.
6. Proposed design equations for wood-steel-wood bolted connections
provide better predictions of the ultimate loads than current design procedure,
especially for bearing.
7. Better predictions for row shear-out can be achieved if the effective
thickness principle is used.
32-7-2 M Ballerini
A new set of experimental tests on beams loaded perpendicular-tograin
by dowel-type joints
Abstract
The results of an experimental programme on the splitting strength of
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.23