CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL ...
CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL ...
CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL ...
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fects. As a summary we may, for the sake <strong>of</strong> simplicity, conclude that the<br />
stress o calculated by elementary theory should be compared with the fracture<br />
material parameter GE. c<br />
28-6-6 T Canisius<br />
End conditions for tension testing <strong>of</strong> solid timber perpendicular to<br />
grain<br />
Abstract<br />
It is specified in the draft CEN Standard prEN1193 that for tension tests<br />
perpendicular to grain <strong>of</strong> solid timber, the platens be pinned with the pin<br />
axis parallel to the grain direction. This is in contrast to the requirement to<br />
have 'clamped' ends for the testing <strong>of</strong> glulam specimens. In this paper, the<br />
reason for this difference in requirements is explained with a finite element<br />
stress analysis.<br />
Conclusions<br />
<strong>–</strong> For tension testing perpendicular to grain in solid timber, it is preferable<br />
to have pinned end conditions than 'clamped' conditions. Such a<br />
choice results in a reduction in stress-concentration related failures at or<br />
near the specimen ends.<br />
<strong>–</strong> In the case <strong>of</strong> glulam specimens, no significant difference can be expected<br />
between results from pinned and clamped end conditions. This is<br />
because <strong>of</strong> their effective vertically symmetric overall nature.<br />
31-6-2 H J Blass, M Schmid<br />
Tensile strength perpendicular to grain according to EN 1193<br />
Introduction<br />
The tensile strength according to EN 384 is derived on the basis <strong>of</strong> a relationship<br />
between tensile strength perpendicular to grain and density:<br />
ft,90,k = 0,001 ρ (1)<br />
Equation (1) leads to higher characteristic tensile strength values for higher<br />
strength classes according to EN 338. In the German timber design code<br />
DIN 1052 the tensile strength perpendicular to grain is independent <strong>of</strong> the<br />
strength class. The same applies to the German National Application Doc-<br />
ument for EC5: a constant value <strong>of</strong> ft,90,k = 0,2 N/mm 2 for all classes is assumed<br />
(for the lowest class S7 ft,90,k = 0). The National Design Specification<br />
(1991) <strong>of</strong> the USA specifies in 3.8.2 " ... designs that induce tension<br />
stresses perpendicular to grain shall be avoided whenever possible. When<br />
tension stress perpendicular to grain cannot be avoided, mechanical reinforcement<br />
sufficient to resist all such stresses shall be considered …".<br />
Ehlbeck and Mirth developed a test method later introduced in EN<br />
1193. The corresponding test arrangement is shown in figure 1 and figure<br />
2.<br />
The tested volume has a cross-section <strong>of</strong> 45 mm x 70 mm and a depth<br />
<strong>of</strong> 180 mm. Intermediate timbers stressed parallel to grain are bonded to<br />
the specimens. Two inductive measuring gauges are attached diagonally.<br />
intermediate wood<br />
test specimen<br />
intermediate wood<br />
Figure 1: Test specimen for tensile strength perpendicular to grain<br />
<strong>CIB</strong>-<strong>W18</strong> <strong>Timber</strong> <strong>Structures</strong> <strong>–</strong> A <strong>review</strong> <strong>of</strong> <strong>meeting</strong> 1-<strong>43</strong> 2 <strong>MATERIAL</strong> PROPERTIES page 2.131