118 / 228
4. STRUCTURAL DESIGN OF LVL STRUCTURES
Table 4.3.
Values of
k
def
for different LVL types in different service classes.
Table 4.2.
Values of k
mod
for LVL (the same values are used for structural timber, glulam and CLT and plywood).
Service class
Permanent
Long-term Medium-term
Short-term Instantaneous
1
0,60
0,70
0,80
0,90
1,10
2
0,60
0,70
0,80
0,90
1,10
3
0,50
0,55
0,65
0,70
0,90
LVL 04, Table 4.3
Product type
Service class 1
Service class 2
Service class 3
LVL-P
0,60
0,80
2,00
LVL-C in edgewise loading
0,60
0,80
2,00
LVL-C in flatwise loading
0,80
1,00
2,50
u
fin
=
u
inst,G
(1+
k
def
) +
u
inst,Q,1
(1+
ψ
2,1
∙
k
def
) +
u
inst,Q,i
(
ψ
0,i
+
ψ
2,i
∙
k
def
)
(4.2)
where
u
fin
is the final deflection including creep deformation;
u
inst,G
is the instantaneous deflection due to permanent
actions;
u
inst,Q,1
is the instantaneous deflection due to the leading
variable action; and
u
inst,Q,i
is the instantaneous deflection due to accompanying
variable actions.
LVL-C has a higher
k
def
value when the loading causes defor-
mation in the flatwise direction due to rolling shear deforma-
tion of the cross veneers similar to plywood. When LVL-C pan-
el is used as a component of stressed-skin panels, the
k
def
value
in the longitudinal direction of the element is the same as for
LVL-P, because the loading causes mainly axial stresses on the
panel.
4.1.6 Design resistance and stiffness
Design resistance in ULS design is determined from the design
values of the strength properties by modifying the character-
istic properties with partial safety factor
γ
M
and modification
factor
k
mod
.
f_d=(k_mod∙f_k)/γ_M
(4.3) (EC5 2.17)
where
f
k
is the characteristic 5% value of a strength property;
k
mod
is the modification factor that takes into account the
duration of load and service class, see Table 4.2; and
γ
M
is the partial safety factor of the material.
Mean values for stiffness properties are used in SLS design
and are determined for short-term loading in service class 1
conditions. The influence of creep deformation is taken into
account by the
k
def
factor. Characteristic 5% stiffness values are
used for stability calculation in ULS design.
4.2 STRUCTURAL PROPERTIES OF LVL
AND STRENGTH CLASSES
The mechanical properties of structural LVL are determined
according to the harmonized product standard EN 14374. The
properties are assessed and their constancy of performance
verified according to the AVPC system 1 of the EU construc-
tion product regulations. LVL suppliers declare their individ-
ual product properties in their Declaration of Performance
(DoPs).
In the future EN 14374 LVL product categories will be
introduced but in the meanwhile LVL industry has decided
to launch them as LVL strength classes. Information about
the strength classes can be found from the Laminated Veneer
Lumber (LVL) bulletin: New European strength classes
15
,
FprEN 14374 Annex B, and these are described in the following
subsections 4.2.1 and 4.2.2.
The bending and axial strength and stiffness properties of
LVL-C with crossband veneers having different layups (i.e. ve-
neer orientation) may be calculated from one set of tests ac-
cording to FprEN 14374 Annex A by applying layup factors
according to Annex C for thickness ranges specified in Annex
A. LVL-C properties are defined with the assumption that the
cross veneers are zero layers.
fin
=
inst,G
(1 +
def
) +
inst,Q,1
�1 +
2,1
∙
def
� +
inst,Q,i
�
0,i
+
2,i
∙
def
�
(4.2)
d
=
mod
∙
k M
(4.3) (EC5 2.17)
(4.2)
fin
=
inst,G
(1 +
def
) +
inst,Q,1
�1 +
2,1
∙
def
� +
inst,Q,i
�
0,i
+
2,i
∙
def
�
(4.2)
d
=
mod
∙
k M
(4.3) (EC5 2.17)
116
LVL Handbook Europe