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– the results given by the two SIF computational approaches are in good
accord, however the ones of the crack closure integral method are more
reliable;
– the analysis of the course of computed SIFs has allowed to highlight the
influence of parameters ar;
– the numerical failure loads derived on the basis of Wu fracture criterion
are in a good agreement with the results of the experimental data;
– the course of these numerical failure loads has allow to highlight the influence
of main parameters (ar, and α) on the splitting strength of
beams also for those cases where testing is problematic because of the
high embedding stresses;
– the fittings made on the course of the numerical failure loads show how
the structure of the prediction formula of van der Put is in a quite good
agreement, the parameters of the power fitting however are different for
the two beam sizes;
– lastly, a relationship between the numerical critical crack lengths and α,
has been derived.
34-7-3 H J Larsen, P J Gustafsson
Dowel joints loaded perpendicular to grain
Abstract
The results of tests with doweled joints in LVL loaded perpendicular to
grain are reported. Four joint configurations were tested: 1, 2 and 3 dowels
in line and 2 dowels side by side. Further tension and splitting properties
perpendicular to grain were determined. Some of the specimens were
stored and tested in standard climate (23 °C/65 % RH) but most were
stored in an open barn in Southern Sweden. The specimens were long-term
loaded in the barn with target load levels relative to the short-term strength
of 65 % and 80 %. Load was applied winter, spring, summer, autumn 2000
and winter 2001 to determine the influence of different climatic conditions.
The main results are: The short-term strength is not influenced by
the seasons. The short-term strength of the joints can be predicted by a
simple equation based on linear fracture mechanics. The load-carrying capacity
of two dowels side by side and a single dowel are identical. The effect
of loading time for joints loaded perpendicular to grain is much more
severe than for timber: the time to failure under a load level of 60 per cent
is only 180 days. A safe load level is only about 30 percent of the short-
term strength. The drying distortions of the specimens used to determine
the tensile strength (40x70x280 m) have a great influence on the results,
the mean value is only 0.67 MPa, the minimum value only 0.25 MPa.
35-7-7 A J M Leijten
Splitting strength of beams loaded by connections, model comparison
Introduction
Initially the problem of perpendicular to grain splitting of beams by connections
was tried solved by empirical models. Lately models based on
fracture mechanics were developed. Empirical models are only valid within
the range of parameters tested therefore there is more credit in pursuing
general physical oriented models. Empirical models for the problem concerned
tend to have many parameters to take all possible influences and effects
into account as is shown by the German model evaluated below. The
last years two models are published both based on fracture mechanical
principles. The first is by Van der Put & Leijten (Papers 33-7-7 and 34-7-
1) the other by Larsen & Gustafsson (Paper 34-7-3).
Model (1) by v. d. Put/Leijten (Eurocode5)
h
Fu � 2,58�b
GGc
1 � h / h
Model (2) by Larsen /Gustafsson
F � 2,82�
b GG h
u c e
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.33
e
Model (3) is a simplified Model (1), see Paper 33-7-7
5,16 � b GG h / h
c e
where:
Fu splitting shear strength of the beam loaded by a connection at mid span
in [N]. For connections at the end of a cantilever the splitting
strength is Fu/2.
b width in [mm]
� behaviour factor
G shear modulus [N/mm 2 ]
Gc fracture energy [N/mm 1,5 ]
h beam depth in [mm]