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General discussion
Moment carrying connections of types that are common in timber portalframes
in Italy meet the requirements of EC8. This statement is made primarily
based on experimental proof that such connections have ductile responses
and because there is evidence that individual dowels in such connections
responded in a ductile manner for levels of deformation likely to
occur within completed building systems. A second point of conformance
with requirements of EC8 is that the degradation to be expected under repetitive
deformations is not excessive.
The above said, it is important to emphasise that dowels employed in
tested connections were relatively slender and therefore developed plastic
deformation in bending. The implication is that assuming compliance with
requirements of EC8 is contingent on connections having slender dowels.
In practice that equates to requiring that connections fail by simultaneous
plastic deformation of dowels and crushing of timber beneath them. Site
quality control must ensure that the correct grade of steel is used because
employing the wrong grade can change the governing failure mechanism
to be brittle (i.e. using higher grade steel could prevent formation of necessary
plastic hinges).
The formulae of EC5 for predicting capacities and stiffness of simple
dowel joints forms a reliable basis from which to predict the behaviour of
tested moment connections and it is therefore presumed those same provisions
are reliable for design.
Conclusions
Experiments have verified that it is possible to design satisfactory moment
connections for two-hinge or three-hinge portal frame structures when effects
of seismic actions must be resisted. In practical terms this means that
the requirement of Eurocode 8 can be complied with. With only slight
modification the connection design provisions of Eurocode 5 can be used
to design such moment connections.
41-7-5 U Hübner, T Bogensperger, G Schickhofer
Embedding strength of European hardwoods
Introduction
The embedding strength tests presented in this paper were realised according
to EN 383:2007 and with the species beech (Fagus sylvatica L.), ash
(Fraxinus excelsior L.) and black locust (Robinia pseudoacacia L.). The
test results will be used to dilate the existing base for the standardisation.
Furthermore, the test results were analysed together with those of other authors.
42-7-4 S Franke, P Quenneville
Embedding strength of New Zealand timber and recommendation for
the NZ standard
Introduction
For all connections it is important to predict the failure strength as accurately
as possible. This includes both the ductile and in some cases especially
in timber construction, the brittle failure as well. For the calculation
of the ductile failure strength, the European Yield Model (EYM) is used in
many standards and accepted as a very accurate model. It forms the basis
of the European timber standard Eurocode 5, EN 1995-1-1:2004.
The development of this is based on a multitude of embedding and joint
tests with different European
and North American wood species by many researchers. Furthermore a
continuous adaptation and improvement is reported overseas such as in
Hübner et al. 2008. The most important parameters for the EYM are the
fastener yield moment and the timber embedding strength, which are
known for most of the softwoods and tropical hardwoods.
In the current NZ timber standard NZS 3606:1993, the design concept
for bolted connections
is not based on the EYM, but depends only on the diameter and the timber
thickness. It doesn’t predict the different types of failure and overestimate
the joint strength partially. There are no embedding strength values, which
can be used for the Johansen’s yield theory to estimate the yield strength
of joints. Furthermore, no formulas are available for the design of joints
with the engineered wood product Laminated Veneer Lumber (LVL),
which uses becomes more important in structural members. To implement
the EYM design concept in the current New Zealand design standard for
mechanical connections, it is thus necessary to investigate the material behaviour
and to determine the embedment values for Radiata Pine timber
and also for Radiata Pine LVL, the two main products used in New Zealand
constructions.
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.29