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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governed by the lower 5th-percentile <strong>of</strong> this group ("weaker material").<br />
In fig. 1 the characteristic bending strength (5th-percentile) depending<br />
on KAR, ovendry density and MOE <strong>of</strong> the laminations is shown for beams<br />
with finger joint failure ( 0 x 5, fi ) and wood failure ( 0 x 5,wood ). The index " 0 "<br />
indicates, that the strength values are valid for a standard beam with a<br />
depth <strong>of</strong> 300 mm. Based on these calculation results, beams with finger<br />
joint failure were found to be the "weaker material" having the lower 5th-<br />
percentile. This tendency even increases with increasing beam dimensions,<br />
because size effects are more pronounced in case <strong>of</strong> beams with finger<br />
joint failure than in case <strong>of</strong> beams with wood failure. This may be explained<br />
by the higher variability <strong>of</strong> strength data in case <strong>of</strong> beams with<br />
failure due to finger joints.<br />
Conclusion<br />
0<br />
Based on the characteristic bending strength fmk , <strong>of</strong> a standard beam under<br />
constant loading, the characteristic bending strength fm,k <strong>of</strong> any glulam<br />
beam may be calculated as<br />
�0,15<br />
� L H � 0<br />
m, k � �<br />
F mk ,<br />
f<br />
where<br />
� �<br />
�5400300� k f<br />
L and H are length and depth <strong>of</strong> the beam in mm,<br />
kF is a load configuration factor (= 1 in case <strong>of</strong> a single span beam with<br />
uniformly distributed load).<br />
The finger joints in the beam have to meet the following requirement:<br />
0<br />
m, k, fj � 1,15 mk ,<br />
f f<br />
It is essential to point out that in case <strong>of</strong> beams, systematically built up<br />
with laminations having significantly different MOE-values, the ultimate<br />
bending stress (in the outermost lamination) must be calculated according<br />
to the theory <strong>of</strong> transformed sections.<br />
23-12-3 H Riberholt<br />
Glulam beams. bending strength in relation to the bending strength <strong>of</strong><br />
the finger joint<br />
Scope<br />
The scope <strong>of</strong> this paper is to illustrate the relation between the bending<br />
strength <strong>of</strong> glulam beams and that <strong>of</strong> the finger joints. It is written as a<br />
contribution similar to that in Ehlbeck & Coling (Paper 23-12-1)which also<br />
deals with this subject. But this paper employs another experimental<br />
source.<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 2.34