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

– WF/Ww: 2:1
The single span three point bending test configuration with rectangular
cross-section and reinforced chord represents possibly an alternative to the
I-cross-section. Mainly there doesn't rise any problem of compression perpendicular
to grain between bottom chord and web. The problem of compression
perpendicular to the grain in the range of the loading can be
solved by lengthening the loading plate. More information has to be gathered,
however, on how the mechanical properties of the material us to reinforce
the flanges influence the strength values which had been quite various
at the tests
35-21-1 B Yeh, T G Williamson
Full-scale edgewise shear tests for laminated veneer lumber
Abstract
The shear strength of laminated veneer lumber (LVL) has traditionally
been determined based on the results of small block shear tests conducted
in accordance with ASTM D 143. In recent years, there has been a significant
interest in determining the shear strength of engineered wood products
using full-scale bending test methods in lieu of small block shear
tests. However, due primarily to different shear-to-bending strength ratios
among a variety of engineered wood products, the use of a prismatic cross
section and test setup similar to those adopted for full-scale shear tests of
glulam does not normally produce an acceptable shear failure rate in the
edgewise or joist orientation (loads are applied parallel to gluelines), as required
for LVL. Therefore, special considerations should be given to the
test setup and specimen configuration for LVL edgewise shear tests.
Conclusions
The following conclusions can be substantiated by the test results presented
above:
– The full-scale test method used in this study is adequate for qualification
of the edgewise shear strength of LVL.
– The difference in the characteristic shear stresses between the specimens
tested at the standard environmental conditions (9.0% moisture
content in this study) and as-received conditions (6.8% moisture content
in this study) are negligible.
– The mean shear strength derived from the ASTM D 143 small block
shear tests is approximately 50% higher than the mean shear strength
determined from full-scale shear tests, suggesting the necessity of considering
a size effect.
– The small-scale QA specimen configuration and test setup used in this
study can be used for edgewise QA shear tests.
38-6-3 H Klapp, H Brüninghoff
Shear strength of glued laminated timber
Introduction
The current knowledge in timber research gives no applicable computation
method for the shear bearing capacity of glued laminated timber beams.
The dependence of the shear strength of the lamination tensile strength, set
in EN 1194, could not be confirmed by the tests of Schickhofer in Graz, so
that in the new German standard DIN 1052 instead a constant value of 3,5
N/mm 2 was set. This value was determined from the test results computationally
as five percent quantile, whereby it is to be stated that about 10
percent of all test results fell below the strength of 3,5 N/mm 2 . In the context
of statistics, this doesn't seem to be alarming. But a negative influence
of the volume on the shear bearing capacity is to be assumed as in the case
of the likewise brittle transverse tension failure. The tests mentioned were
conducted on comparatively small beams, so that lower shear strengths for
dimensions of practical use can be supposed.
In view of this uncertainty concerning the shear strengths as well as the
current cases of damage, there is an urgent need for further research. However
larger test series with practical dimensions are costly in terms of resources
and labour. For this reason the alternative solution of a simulation
model, which considers the varying material properties, was selected.
Simulation model
The simulation model is based on the assumption that the shear strength of
glued laminated timber depends on the properties of the laminations. In
contrast to EN 1194 a dependence not on the tensile strength is supposed,
but on shear strength. Furthermore brittle fracture behaviour is applied by
assuming failure as soon as the shear strength of the lamination is reached.
According to this the shear strength of a glulam beam can be easily determined
by comparing the shear stresses of the laminations with the corre-
CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL PROPERTIES page 2.115