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

ters for all grades and species. Size parameters are also independent of
property level. The only major inconsistency observed in the results, as
presented in this paper, is the difference in size factors for compression
which may be due to the significant size difference in test specimens
employed.
– Size factors for adjusting test data or modifying code design properties
size must be expressed in a manner consistent with the associated test
standards. If test standards employ members of constant length to width
ratios then the size factors will be different than would be employed
with constant length test members.
– The CWC test data suggests that a size parameter of the order of S = 0.2
could be applied for bending and tension width and length effects. The
size parameter S = 0.1 could be applied for compression width and
length effects. These size factors would provide a basis for developing
a set of simplified expressions for adjusting tension, bending and compression
strength data for both data interpretation and code docurnents.
22-12-1 M Badstube, W Rug, W Schöne
The dependence of the bending strength on the glued laminated timber
girder depth
Introduction
With a view to determining the influence of the girder depth on the bending
strength of glued laminated' timber, experimental investigations and
tests are being carried out. It is the objective of these tests and investigations
to find out data and information concerning the 'application of the
"depth dependence" modification factor kh (depth factor) for glued laminated
timber
Summary
The evaluation of the bibliography (publications) and our own specific
tests and investigations performed by means of glued 1pminated timber
girders are demonstrating that for the failure type A ("finger joint") failure
within the stressed zone) there doesn't exist any interrelation between the
girder depth and bending strength.
As for the failure type B (knot or timber failure within the -heavily
stressed zone), a statistically covered and verified interrelation between the
stressed volume or girder depth and the bending strength can be determined:
The tests are verifying the depth factor as indicated in the Eurocode 5
for the failure type B.
23-10-3 J D Barret, A R Fewell
Size factors for the bending and tension strength of structural timber
Introduction
For many years it has been recognized that the bending strength, and more
recently tension strength, of timber are affected by the size of the specimen.
While this effect may in reality be associated with the stressed volume,
grade, and the size and age of the tree from which it was cut, it is
generally described as a depth effect (for bending) or a width effect (for
tension).
This paper examines the available test data to determine the effect of
length and depth or width on bending and tension strength and provides
depth and width factors applicable to Eurocode 5 and the supporting CEN
standards.
Conclusions and recommendations
From an analysis of test data comprising many different grades and species,
the following conclusions were reached:
– The factor (k) for adjusting characteristic values in codes and standards
for both the depth effect on bending strength and the width effect on
tension strength, when each in property is based on a constant span to
depth ratio, is given by
k = (200/h) 0.4
where h is the depth or width of the member for which the strength value
is required.
– In using the factor given above a minimum size of around 35mm x
47mm needs to be specified for tension members.
– The factor (kW) for adjusting tension or bending stresses to other depths
or widths, when the length remains constant, is given by
kW = (A/ B ) 0.23
where A is the width or depth relevant to the stress value to be adjusted
and B is the width or depth relevant to the required stress value.
CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL PROPERTIES page 2.123