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The results of the evaluation are compared with work previously reported
by others to CIB W18A. They are also discussed briefly in relation
to current design recommendations.
Conclusions
Tests and analytical investigations have been made on load distributions in
multiple-fastener bolted joints, using European whitewood glulam, with
steel side plates. The proportions of load carried by each bolt have been
determined. These have been found to be very uneven, especially in the
perpendicular to grain case.
For each of the three modes of loading which were investigated, namely
compression parallel to the grain, tension parallel to the grain, and compression
perpendicular to the grain, reduction factors have been determined,
by test and from analysis. These reduction factors were related to
the type of calculation which is based on summing the load carrying capacity
of a multiple-fastener joint by taking the number of fasteners multiplied
by the individual fastener capacity.
In compression parallel to the grain, the reduction factor determined by
test was only about four per cent different from the corresponding value
shown by analysis. In the tension case, agreement was within ten per cent.
In compression perpendicular to the grain, agreement was less close, with
a difference of twenty two per cent between test and theory. However, this
is still considered quite reasonable, in view of the substantial influences
tending to cause variability in such specimens.
The experimental measurements were conducted using a special test
apparatus, which was designed to ensure that failure took place in a pure
embedment mode. Other precautions were also taken in manufacturing the
specimens. Single-fastener tests were conducted which were then compared
with EC5 (draft) design procedures. These comparisons showed that
the plastic embedment assumption was valid.
Both the tests and the analysis suggested that the load sharing amongst
the fasteners was more even in the case of tension parallel to the grain,
than in the case of compression parallel to the grain. The reduction factor
for compression perpendicular to the grain was substantial, and should apparently
be even more severe according to the finite element analysis than
was determined by test. The test evidence suggested that a reduction factor
of 0.50 should apply to four bolts in such a situation.
The reduction factors determined for the various four-bolt parallel to
grain configurations in this research were in the range 0.66 to 0.89. A brief
comparison with two other sets of tests was made in this paper, and in an
accompanying paper, a selected review of research and codes was given.
All the supporting evidence suggests that BS 5268:Part 2 and EC5 (April
1992 Draft) make insufficient allowance for this phenomenon..
30-7-5 A Jorissen
Multiple fastener timber connections with dowel type fasteners
Abstract
The load carrying capacity of a connection with a number of fasteners, a
so called multiple fastener connection, does generally not equal the load
carrying capacity of a single fastener multiplied by this number. Often the
connection fails at a lower load because the timber splits. The result can be
a brittle failure. The geometrical parameters, material properties and the
number of fasteners determine the load carrying capacity and the type of
failure.
To investigate the governing parameters a comprehensive research,
both theoretical and experimental, started at the Delft University of Technology
at the beginning of 1994.
About 950 tests on single and multiple bolted connections have been carried
out. The tests will be presented and discussed.
Introduction
This paper deals with the load carrying capacity of multiple fastener timber
connections, timber to timber, with dowel type fasteners in a row parallel
to the grain. Symmetrical double shear connections are studied. The
connection is in the grain direction.
The fact that the load carrying capacity of a multiple fastener connection,
Fmultiple, does not equal the load carrying capacity of a single fastener
connection, Fsingle multiplied by the number of fasteners n is taken into account
in many national design codes. An effective number of fasteners nef
< n) has been introduced. Fmultiple, is calculated according to equation:
Fmultiple = nef Fsingle
In most countries Fsingle is calculated according to the so called European
Yield Model, first described by Johansen, which allows nef, as defined in
the national design codes, to be compared. Hardly any agreement on the
design values for nef exists. Even if the background of the design rules is
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.61