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4.14 SLOTTED-IN STEEL PLATES
30-7-3 E Aasheim
Cyclic testing of joints with dowels and slotted-in steel plates
Background and objective
In this paper tests performed in the project "Joints for Timber Bridges" are
described. This project is a part of the "Nordic Timber Bridge Program".
The objectives of the project were to evaluate and develop mechanical
fasteners with regard to dynamic actions and moisture conditions. Different
types of fasteners were considered, and it was soon clear that the project
had to be limited to one main type of joints. The project team chose to
concentrate the work to testing of joints with steel dowels and slotted-in
steel plates exposed to dynamic loads. The main reasons for this were that
these joints are heavily used for timber bridges and that this type of joints
is typical for all kinds of dowel type fasteners.
Few test results concerning dynamic testing, of joints are available. In
the draft for Eurocode 5 - Design of timber structures - Part 2: Bridges,
k fatigue for joints are introduced. k fatigue is a factor to transform characteristic
short term static strength to characteristic strength for dynamic loads,
k fatigue . The aim of the project was to obtain more detailed information
about k fatigue than those indicated in Eurocode 5. By studying draft Eurocodes
and national design rules, the maximum number of load cycles during
testing was set to 10 7 . The tests were performed to determine the load
level where the dynamic loading resulted in rupture at this number of cycles.
Recommendations and conclusions.
No guidelines for fatigue testing of timber joints are found in Eurocode 5
or in other documents known to the project team. The tests described in
this report may be regarded as a first proposal from the project team about
how to test and evaluate joints with regard fatigue actions. The experience
gained during the testing shows that many factors should be discussed and
that further research and tests are desirable. Some of the factors that are
not investigated in this project are:
– Different failure modes
– The difference between reversed and non-reversed cycling
– The influence of the steel quality of the dowels
– Other dowel diameters.
– Other angles between the load and the direction of the grain
– The effect of several dowels in line with the load direction
– The effect of the frequency of the load cycles
– The effect of temperature and moisture content in the specimen.
The load levels in the range from 10 6 to 10 7 load cycles are slightly higher
than k fatigue � 0,25 from Eurocode 5. In other words, Eurocode 5 seems to
give values on the safe side.
30-7-4 E Gehri
A steel-to-timber dowelled joint of high performance in combination
with a high strength wood composite (parallam)
Introduction
A lot of research work has been done and is still going on for the development
of high strength wood composites like Parallam. The main problem
consists now in the transfer of larger forces in such materials, i.e. the
development of adequate connections of high performance and reliability.
The Blumer system (BSB), a steel-to-timber dowelled joint, developed and
mainly used for connections in glued laminated timber of spruce, showed
to be also adequate with Parallam.
BSB-connections
Two types of BSB-connections were used (see figure 1): with 3 and 4 steel
plates. The number of dowels in a row varied between 3 and 5. Besides the
normal BSB-dowel (diameter 6,25 mm and nominal tensile strength of 550
N/mm 2 ) a serie was made with diameter 6,0 mm and ETG-steel (nominal
tensile strength of 1000 N/mm 2 ).
Conclusions
The BSB connections are meanwhile (the tests with Parallam were made
in 1991) made with a distance of the steel parts of 60 mm. Using normal
BSB-dowels a slightly higher load-carrying capacity is achieved.
The connection length is – independent of the section – when using 4
dowels in a row only about 220 mm, which is a very short connection.
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.81