62 veneers LVL in flatwise and edgewise direction. Figure 39 and 40
indicate that BING vibrating method was a reliable non-destructive instrument to help
predicting LVL MOE of poplar and douglas-fir both for 3mm and 5.25mm veneer. Our results indicated that dynamic MOE was higher compared to static MOE. It
was also noted in other studies that dynamic MOE using Timoshenko approximation is slightly higher than static MOE on poplar and beech El-
Haouzali
2009 ; Daoui et al.
2011 . This phenomenon could be due to in dynamic
MOE values were resulted from Timoshenko model by taking into account the bending moment, shear and rotational inertia.
Figure 40 Correlation between dynamic MOE vibration method and static MOE four-point bending test for LVL 140 samples made of douglas-fir
4.7.3 Modulus of Rupture MOR
The ANOVA Table 18, showed that all factors significantly influenced poplar MOR p0.01. LVL made of mature veneer 55 MPa resulted in a higher
MOR value than juvenile veneer 47 MPa. The strength MOR of laminated wood assembled with high density
veneers tends to be greater than that made of low density veneers, which was also observed for solid wood samples by Reuling et al. 2013.
According to Duncan’s multiple ranges Appendix 2, ‘Alcinde’ and ‘Lambro’ had the same highest value for MOR 58 MPa, while ‘Dvina’, ‘Triplo’
and ‘I214’ had approximately the same value 45 MPa considered the lowest. The average MOR values for 5.25 mm LVL 49.6 MPa and 3 mm LVL 51.4
MPa were statistically different Appendix 2. The flatwise position 52 MPa gave a higher MOR value than the edgewise position 49 MPa. According to
Duncan’s multiple ranges Appendix 2, those values were statistically different. The effect of lamination improved the tensile limit of these cultivars by
about 20 on average compared to solid wood Rahayu et al. 2013. Poplar LVL properties can be influenced considerably by the cultivar, the glue type and the
veneer thickness El-Haouzali 2009. According to El-Haouzali 2009, the site does not provide any significant effect.
Poplar LVL made of mature veneer resulted in a higher MOR value than juvenile veneer. Indeed, because of the specific physical and mechanical
properties of juvenile wood, its proportion can have a significant impact on wood mechanical properties such as lumber strength Panshin and de Zeeuw 1980.
y = 0.906x + 696.56 R² = 0.7453
5000 10000
15000 20000
25000
5000 10000 15000 20000 25000
Dy nam
ic MO
E MP
a
Static MOE MPa
63 The average poplar MOR values for 5.25 mm and 3 mm LVL were
statistically different Appendix 2 in line with the results of H’ng et al. 2010 who reported that LVL with thinner veneers 15 plies had better mechanical
performances compared to those of thicker veneers 11 plies. However, the improvement was still limited in that case and could be attributed mainly to the
upgrading of lamination effects and to the reduction in lathe check depth. This improvement was also limited because the material used was almost free of defect
such as knots.
As observed in the literature Daoui et al. 2011; El-Haouzali 2009, the flatwise position gave a higher MOR value than the edgewise position. It was due
to multiple aspects such as the number of veneer layers, the adhesive and the pressure during manufacture had led to higher MOR values in flatwise position.
The ANOVA Appendix 4 shows that all factors significantly influenced douglas-fir MOR LVL p0.01. Average value of MOR are presented in
Appendix 5, MOR 57 + 9 MPa of douglas-fir LVL made of juvenile veneers was significantly lower than MOR 63 + 9 MPa of LVL made of mature. This
corresponds to results from many authors Barrett and Kellogg 1989; Kretschmann et al. 1993; Nazerian et al. 2011.
Figure 41 Douglas-fir LVL failure break on glue line after destructive bending strength test by instron
Douglas-fir LVL MOR 57 Mpa of LVL 3mm was significantly lower than MOR 63 Mpa of LVL 5.25mm. The LVL 3mm suffered severe failure on glue
line after destructive bending strength test by INSRON Figure 41. Although, those samples were excluded from the statistical analysis, we suspected the LVL 3
mm had lower shearing strength compare to LVL 5.25 mm. The results of this work were in line with Echols and Currier 1973 who find that MOR of solid
Douglas-fir is higher compared to 5-ply LVL Douglas-fir and MOR of 5-ply LVL is higher compared to 7-ply LVL Douglas-fir.
Doulgas fir LVL MOR 58 Mpa of flatwise position was significantly lower compare to MOR 62 Mpa of edgewise position. It was due to most of wood
failure on flatwise direction was shear failures. This phenomenon is also noted by Krestchmann et al. 1993 who states flatwise bending strength of Douglas fir
LVL is 11 less compare to edgewise LVL samples.
4.7.4 Specific MOE SMOE and Specific MOR SMOR
Several researchers have used specific modulus of rupture SMOR and specific modulus of elasticity SMOE to evaluate MOE and MOR results by
