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Within the GIROD-project the work is focused on rods glued-in with three
different adhesive types: two-component epoxy (EP), two-component polyurethane
(PUR) and phenol-resorcinol-formaldehyde (PRF). Mainly steel
rods were used within the project bi also some fibre reinforced plastic rods
(FRP) were tested.
The description of the GIROD-project given here is based on the project
structure give above.
Objectives
The objective of the GIROD project is to provide the information required
to prepare
standards that will allow an increased, more advanced and more reliable
use of glued-in
rods in timber structures. When the project started the working plan was as
follows:
12. Perform theoretical and experimental work leading to a calculation
model for axially loaded glued-in rods based on the adhesive bond
properties as well as the wood and rod material properties. This must
take into account the effect of varying climatic and loading conditions
as well as fatigue. This step will give information required by CEN
TC250/SC5 in the preparation of Eurocode 5 - Design of Timber Structures.
13. Develop test methods for the evaluation of adhesives for glued-in
rods with respect to strength, durability, creep and creep rupture behaviour
under different climatic conditions. This will support the work of
CEN TC193/SC1.
14. Derive test methods for the production control of structural glued-in
rod connections. This will support the work of CEN TC124/WG6.
15. Development of a calculation model.
Conclusions
– A calculation model based on a combination of Volkersen theory and
fracture mechanics gives good prediction of the pull-out strength for
adhesives that bond to the rod such as PUR and EP. The pull-out
strength is controlled by two material property parameters that can be
easily determined in full-scaled pull-compression tests.
– Fatigue is a significant factor in the performance of glued-in rods and
needs to be considered in applications like for instance bridges. Failure
can occur in the rod, in the adhesive bond line, in the wood substrate
and in the interface between wood and adhesive.
– The effect of rod spacing and edge distances have been clearly demonstrated
and proposals to be used in design have been made.
– Storage without mechanical loading in variable outdoor climates had a
strength reducing effect mainly on PUR-bonded rods. After storage in
85 % RH the PRFbonded rods were most affected.
– Glued-in rods have a DOL behaviour that can differ quite considerably
from that of timber and other timber connections. In 85 % RH the behaviour
of EP-bonded rods behaved like the Madison curve while PRF
and PUR had much shorter time to failure. At 50 °C the PRF behaved
in a better way than PUR and EP.
– It is questionable if the method developed for evaluation of the durability
of adhesives for glued-in rods is suitable for the purpose. PRF,
which is known to give very durable wood-to-wood bonding, obtains
extremely low strength values after testing in wet conditions. It seems
that the method punishes adhesives that do not bond to the rod.
– The creep-rupture test method developed for small specimens works
well. The creep-rupture behaviour of small specimens compared to this
behaviour for full-sized specimens will be further investigated.
– A simple production control test method based on proof-loading has
been developed. It is able of detecting a number of serious production
errors.
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.53