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4.12 STATISTICAL TREATMENT
37-7-13 A Kevarinmäki
Behaviour of fasteners and glued-in rods produced from stainless
steel
See: 4.6 Glued-in rods
37-7-12 A J M Leijten, J Köhler, A Jorissen
Review of probability data for timber connections with dowel-type fasteners
Introduction
In the European design standard, Eurocode 5 (EN1995-1-1) the Johansen
model is presented to predict the strength of connections with dowel-type
fasteners. This model contains besides a number of geometrical parameters
two material parameters; the embedment strength of the timber and the
yield moment of the fastener. This study focuses on the main influencing
independent parameters of the embedment strength being; the timber density
and diameter of the fastener. The embedment strength expressions in
Eurocode 5 are based on a comprehensive study by Whale and Smith
(1986b) and Ehlbeck and Werner (1992). The influence of the timber density
and the fastener diameter was derived using regression analyses. Expressions
for the lower 5 %-Fractile value were assumed to be the same as
for the mean value. This was achieved by simply exchanging in the regression
formula the mean value of the density by the lower 5%- Fractile value
of the density.
In the present study embedment test results from the above-mentioned
research and test data from later investigations are considered to create a
probabilistic framework for the prediction of the embedding strength. The
presented framework is applied in a reliability analysis of a simple dowel
connection. The lower 5%-Fractile of the embedding strength is introduced
to characterize the evaluated probability distribution of the embedding
strength. This information can be used to be incorporated in probabilistic
design codes to feed design models of timber connections.
Conclusions regarding the results
From the evaluation of the analyses results it can be concluded that:
– Caused by differences in definition of the embedment strength perpendicular
to grain a large portion of the available database was unsuitable
for evaluation.
– A framework for the evaluation of the probability distribution of the
embedding strength is presented for given 5%-Fractile value of the density
and the diameter of the fastener is presented. In doing so it is distinguished
between timber family, loading direction and fastener type.
– The 5%-Fractile value of the probability distribution is quantified to
characterize the distribution.
– Applying the method in a reliability analysis with a simple connection,
acceptable results for the failure probability can be obtained.
38-7-2 J Köhler
A probabilistic framework for the reliability assessment of connections
with dowel-type fasteners
Introduction
For timber structures, the structural performance depends to a considerable
part on the connections between different timber structural members; connections
can govern the overall strength, serviceability and fire resistance.
Assessments of timber structures damaged after extreme events as storms
and earthquakes often point to inadequate connections as the primary
cause of damage. Despite their importance codes and regulations for the
design of timber connections, however, are not based on a consistent basis
compared to the design regulations of timber structural components.
In the daily practice the engineering codes and regulations form the
premises for the use of timber as a structural material. Code regulations in
North America, Australia and Europe are based on the limit states design
(LSD) approach which is implemented via load and resistance factor design
(LRFD) formats. Originally, LRFD methods where converted as so
called "soft conversions" of allowable stress design (ASD), the design
method which was commonly used in code regulations before LRFD was
introduced and which is usually based to a major part on experience, tradition
and judgment. In the last decade this situation was changed by the use
of structural reliability concepts as the basis of design of timber members.
This progress was possible by means of collecting a huge amount of ex-
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.74