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– spacing rules between rods and between rods and timber edge for axial
and lateral load,
– design rules for glued-in rods parallel or perpendicular to the grain and
axially loaded,
– design rules for glued-in rods parallel or perpendicular to the grain and
laterally loaded,
– rules for glued-in rod production,
– constructive dispositions.
But, in France, the use of glued-in rods in building constructions is limited
because:
– there is no evaluating adhesive method for glued-in rod technology,
– there is no production control test method,
– and there is no knowledge on long term behaviour on this technology.
So, a national research project (2002-2004) is carrying out in collaboration
between CTBA, LRBB and the French Glued laminated Timber Syndicate
to provide the knowledge required to elaborate these documents.
The main works of the national project are:
– short and long term tests on full size specimen,
– short term and long term tests on small pieces,
– development of finite element model to describe mechanical behaviour
including temperature and moisture content evolution into glued-in rods
specimen submitted to natural temperature variations.
Two commercial adhesives are tested:
– a two-components Epoxy
– a two-components CR 421 from Prubond.
For all experiments of the national project:
– specimen are tested in axial load with rods glued parallel to the grain,
– GL24 wood quality with 12 mm threaded rod was used (chosen by
glued laminated producers),
– spacing rules between rods and between rods and timber edge for axial
and lateral load was the one specified in the French Guide,
– specimen manufacturing was made by glued laminated producers according
to production rules given by adhesives producers.
37-7-13 A Kevarinmäki
Behaviour of fasteners and glued-in rods produced from stainless
steel
Introduction
In addition to better durability the use of stainless steel improves the fire
resistance of connections. The stainless steel has good fire resistance properties.
Unprotected stainless steels have enough capacity in fire resistance
class R30 and certain titan stabilised grades also in class R60 without over
design in normal temperature. So the fire protections and/or groovings of
the effective cross-sections of timber members for the connections may be
avoided with the use of stainless steel. However, also in normal temperature
the design rules of timber fasteners are normally given only for the
non-alloy steel. The stainless steel grades have a low 0,2 -yield value
(normally 220 N/mm 2 ) but a high tensile strength (even > 800 N/mm 2 ) )
with the ultimate elongation more than 40 %. The paper summarizes the
results of the research done for the verification of the design rules for the
stainless steel fasteners in normal temperature.
Conclusions
The main result of the research was that the ultimate tensile strength of
stainless steel may be fully utilized in the design of the connections of
timber structures. The Eurocode equations of yield moments may be safely
used for stainless steel fasteners with the ultimate tensile strength of stainless
steel. However, for full utilization of the stainless steel fastener capacity,
it is advisable to use the tested yield moment values for the actual fastener
type and dimension. The stainless steel material may be significantly
strengthened in the manufacturing of certain type of stainless fasteners
(e.g. threaded nails). Also the strain hardening occurred in the bending of
the stainless fasteners may be utilized by using the tested yield moment
values. The high ductility and strain hardening of stainless steel fasteners
improve the capacity and behaviour of the connections of timber structures.
The withdrawal strength of stainless nails and screws is practically the
same as with similar non-alloy fasteners, although the edges of fasteners
profiles are generally slightly more round with stainless fasteners. However,
the present new version of Eurocode 5 (prEN 1995-1-1:2003) gives
about two times too high withdrawal capacity values for the common selftapping
screws loaded perpendicular to the grain. It is also in conflict with
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.55