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have been varied. Minimum values of those in V-connections are proposed.
Concluding Remarks
Design method is proposed for the V-connections, in which the steel rods
are glued at skew angles into the glulam. It is based on large test series.
The V-connection is not vulnerable to splitting of wood in the anchorage
area. Due to limited variation the anchorage strength of the rods can have a
high design value in all grain direction bigger than 15 º . The calculated
dowel capacity of the rods with a steep direction angle also can be added
to the vector sum of the capacities of the rods forming V-shape.
V-joint is quite rigid. However, like mechanical joints it has ductile
properties due to yielding of the longer rod. The capacities of V-joints can
be summed without reduction on the condition that the anchorage length
allows yielding of the rods. The connection can carry bending moments up
to the capacity of the glulam and is not vulnerable to splitting of the wood
in the joint area. The tensile capacity of timber shall be checked for the
tensile force in the connection. The tensile force perpendicular to grain
shall be designed separately
33-7-11 R J Bainbridge, K Harvey, C J Mettem, M P Ansell
Fatigue performance of bonded-in rods in glulam, using three adhesive
types
Abstract
Bonded-in rods are an economical and architecturally and industrially attractive
means of forming connections within a timber structure, and of
providing local reinforcement to critical zones of timber members. They
also provide an important technology for the repair and upgrading of historically
important timber structures that exist throughout Europe.
Structures are subject to variable actions throughout their design lives,
which normally result in the repeated development of stresses below the
ultimate strength of the material. There is however a theoretical potential
for failure to be induced even at low stress levels, due to fatigue.
This paper presents the findings of experimental investigations in relation
to the use of commercial adhesives to bond threaded steel rods into
oversized holes in order to achieve structural timber connections. The
work is part of the European Union supported GIROD project, which aims
to develop design rules for inclusion in Eurocode 5.
Three types of adhesive are considered – an epoxy, polyurethane and a
filled phenol resorcinol formaldehyde, in tests whereby threaded steel rods
were axially loaded in a variable tension cycle whilst bonded parallel to
the grain of a host glulam member. Fatigue lives are examined for two geometries
of test specimen and results from different failure modes are
compared to the theoretical performance of the component materials.
Four potential failure modes were identified (timber failure, cohesive failure
at timber/adhesive interface, bond line failure and steel rod failure), all
of which were observed within a single geometry of specimen. It is
demonstrated that the adhesive type has a clear influence upon both the fatigue
life and the likely failure mode.
Conclusions
A revised basis for design of bonded-in rods for structural timber connections
is under preparation through the GIROD project. This draws heavily
upon both existing knowledge and experimental investigation. The fatigue
behaviour discussed herein is an area where experimental investigations
are adding to the knowledge of these systems and expanding the scope of
addressable issues in their design.
The structure of the Eurocodes provides opportunities to link-in test evidence
to design methods in both of the instances discussed, primarily due
to the explicit nature of the code formulation and the more fundamental
link between limit states basis and material properties observed directly
from tests.
Observations and projected fatigue lives presented herein must be taken
in the context of extrapolations based upon a limited data set, lacking confirmatory
data at high numbers of load cycle.
The majority of fatigue failure modes were common to those observed
in static test counterparts to the fatigue test specimens. Significant incidents
of alternative failure modes were, however, also recorded, especially
failures in the steel rods.
It is apparent that different adhesive types behave in fundamentally different
ways with respect to the fatigue performance and the eventual mode
of failure at the fatigue ultimate limit state.
The geometry of the test specimens is at least as important under the
conditions of this test as the adhesive type, but the general order of per-
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.51