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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Conclusions<br />
The following conclusions can be made from the limited analyses carried<br />
out so far with respect to beam strengths.<br />
<strong>–</strong> The present project on the determination <strong>of</strong> along-member beam<br />
strengths seems to provide good prospects for the calculation <strong>of</strong> moment<br />
configuration factors.<br />
<strong>–</strong> It is desirable to gather information on the way and the extent to which<br />
the strength reductions due to defects may spread along a beam.<br />
<strong>–</strong> It is advisable to have information on the possible strength coefficients<br />
<strong>of</strong> variation (COVs) with respect to the regression analysis predictions.<br />
<strong>–</strong> It is necessary to study the effect <strong>of</strong> the possible subjectivity <strong>of</strong> manually<br />
selected defect positions on the generated strength results. This<br />
subjectivity occurs for beams with many smaller close depressions in<br />
the graph <strong>of</strong> force vs. the beam length.<br />
<strong>–</strong> The determination <strong>of</strong> valleys in the grading machine readings, which<br />
may correspond to defects, need to be automated. For this purpose objective<br />
criteria need to be developed.<br />
<strong>–</strong> Firmer conclusions can be made only when the strength predictions <strong>of</strong><br />
all the 133 beams are simulated and a statistical analysis <strong>of</strong> results is<br />
carried out.<br />
28-12-2 E Aasheim, K H Solli<br />
Size factor <strong>of</strong> Norwegian glued laminated beams<br />
Background<br />
A research project where the aim was to determine the size factor kh, <strong>of</strong><br />
Norwegian glued laminated beams has been carried out by The Norwegian<br />
Institute <strong>of</strong> Wood Technology in co-operation with two Norwegian producers<br />
<strong>of</strong> glued laminated timber. The purpose <strong>of</strong> this project was to compare<br />
the laboratory results with the corresponding values <strong>of</strong> kh given in<br />
Eurocode 5:<br />
h<br />
� � 0,2<br />
600<br />
k � h<br />
with the following limits: 1�kh� 1,15<br />
The limits correspond to h = 600 mm ( kh � 1)<br />
and h = 300 mm (<br />
k � 1,15 ).<br />
h<br />
Conclusion<br />
Based on Eurocode 5 it should be expected that<br />
kh � fm, k,300 fm,<br />
k,600<br />
� 1,15<br />
The result from this project shows a lower value <strong>of</strong> k h . By using the values<br />
from the Weibull-3 parameter distribution the following value <strong>of</strong> k h<br />
was given for a depth <strong>of</strong> 300 mm:<br />
f mk , ,300 34,1<br />
� � � 1,07<br />
f 32,0<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 2.128<br />
k<br />
h<br />
mk , ,300<br />
The corresponding size factor calculated from the mean values was<br />
kh � 1,12 .<br />
Based on observations <strong>of</strong> the lamellae and their distribution <strong>of</strong> defects it<br />
is assumed that much <strong>of</strong> the size effect can be explained by the test method<br />
and the grading accuracy.<br />
If this assumption is correct, then the size factor k h is not only a function<br />
<strong>of</strong> the depth, but also <strong>of</strong> the grading accuracy and the strength class.<br />
29-6-1 N Burger, P Glos<br />
Effect <strong>of</strong> size on tensile strength <strong>of</strong> timber<br />
Introduction<br />
When designing timber members according to Eurocode 5 the size <strong>of</strong> the<br />
member has to be taken into account by means <strong>of</strong> size factors. These factors<br />
were derived from investigations mainly carried out in North America<br />
and Great Britain using wood species and grading rules common in these<br />
countries. Since it is most likely that size effects may also depend on wood<br />
quality, grading rules and, perhaps, wood species, the purpose <strong>of</strong> this study<br />
was to investigate whether these size factors also apply to wood species<br />
and grading rules currently in use in Germany.<br />
Towards this end the influence <strong>of</strong> specimen size on the tensile strength<br />
was investigated using 750 specimens from timber <strong>of</strong> native spruce and<br />
200 specimens from timber <strong>of</strong> native Douglas fir, with varying crosssectional<br />
dimensions and lengths.<br />
Discussion <strong>of</strong> Results<br />
Results from the tension tests conducted in the course <strong>of</strong> this study reveal<br />
systematic effects <strong>of</strong> specimen dimensions on tensile strength. On the one<br />
hand tensile strength decreases with increasing test length, which corre-