CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL ...

Conclusion
The relation between the bending strength of glulam and that of the finger
joints seemsto depend on several factors. Among these are partly the size
of the finger joints represented for example by the thickness of the lamination,
partly the relation between the strength of the finger joint and that of
the rest of the lamination. This could be explained by the fact that the
weak finger joint is brittle and the surrounding wood is in the linear state
so stress redistribution will not take place.
23-12-4 H Riberholt, J Ehlbeck, A Fewell
Contribution to the determination of the bending strength of glulam
beams
Preface and explanation
In the draft it has been necessary to introduce 2 tables of strength classes,one
for glulam with a homogeneous cross-section and one for glulam
where different lamination grades have been combined in the crosssection.
The last mentioned is frequently employed in practise and it could
be preferable to standardise this set of strength classes.
Another possibility would be to have more classes so that homogeneous
and combined grades could be included in the same table of classes. But
this solution would give some problem with the setting of the strength values
for axial tension and compression. These would have to be set at a rather
low level in order to cater for the combined grade glulam with the low
quality inner laminations. This would penalise homogeneous glulam.
Introduction
A strength class system enables combinations of grade and species having
similar strength properties to be classified together with a common set of
strength properties. Such a system simplifies the process of marketing
structural timber by reducing the number of options at the specification/supply
interface.
24-12-1 F Colling, J Ehlbeck, R Görlacher
Contribution to the determination of the bending strength of glulam
beams
Introduction
This paper intends to summarize the results of the extensive research work
done in Karlsruhe (Germany) on the bending strength of glulam beams.
Above all it is the aim of this essay to develop design rules for glulam
beams under bending.
The bending strength of glulam beams is primarily governed by two
properties:
– the quality of the laminations used;
– the strength of the finger joints
This is repeatedly demonstrated and proved by numerous tests in different
countries. In order to make the problem easier to understand how the
bending strength of glulam beams is influenced by mixing these two properties,
it seems useful to consider first of all both effects separately.
Conclusion
It can be summarized that for aiming at certain glulam strength classes the
minimum requirements for the laminations and the finger-joints, as given
in Table 8, may be used.
Table 8: Requirements to comply with some glulam strength classes
Glulam strength class LH 25 LH 30 LH 35 LH 40
Strength class of the laminations C 18 C 24 C 30 C 37
Requirements due to finger joints:
ρ >
MOE >
CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL PROPERTIES page 2.35
none
none
390
9000
440
12000
ρ = mean density in kg/m 3 (moisture content u = 12%). MOE = mean
lengthwise MOE in N/mm 2
510
15000