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4. STRUCTURAL DESIGN OF LVL STRUCTURES
In the case of rectangular cross sections:
I_tor=k_1∙h∙b^3
(4.43)
Table 4.9.
Effective length as a ratio of the span (Modified from EC5 Table 6.1.).
The equation (4.42) of
σ
m,crit
may be replaced by a simplified
equation:
σ_(m,crit)=(c ∙ b^2)/(h ∙ l_ef ) E_0,05
(4.45)
where
c
is 0,58 for LVL 48 P and 0,67 for LVL 36 C;
b
is the beam thickness [mm]; and
h
is the beam height [mm].
Note: More advanced design instructions for LTB can be found
from manufacturers’ technical documentation.
4.3.10 Notches
The effects of stress concentrations at the notch shall be tak-
en into account in the strength verification of members. The
effect of stress concentrations may be disregarded in the fol-
lowing cases:
• Tension or compression parallel to the grain;
• Bending with tensile stresses at the notch, if the taper is not
steeper than 1:
i
= 1:10, that is
i
≥10, see Figure 4.20 a);
• Bending with compressive stresses at the notch, see Figure
4.20 b)
Figure 4.19.
Installation of notched rafter beam.
where
k_1=1/3 (1-(0,63∙b)/h)
(4.44)
k
1
= 0,14 for square cross sections;
k
1
= 0,23, when h/b = 2;
k
1
= 0,28, when h/b = 4 and
k
1
= 0,30, when h/b = 6
k
1
= 0,31, when h/b = 10
tor
=
1
∙ ℎ ∙
3
(4.43)
1
=
1 3
�1 −
0,63∙ ℎ
�
m,crit
=
∙
2
ℎ ∙
ef
0,05
1
=
1 3
�1 −
0,63∙ ℎ
�
(4.44)
m,crit
=
∙
2
ℎ ∙
ef
0,05
(4.45)
LVL 04, Table 4.9
Beam type
Loading type
l
ef
/
l
a
Simply supported
Constant moment
1,0
Uniformly distributed load
0,9
Concentrated force at the middle of the span
0,8
Cantilever
Uniformly distributed load
0,5
Concentrated force at the middle of the span
0,8
a
The ratio between the effective length lef and the span l is valid for a beam with torsionally restrained supports and loaded at
the centre of the gravity. If the load is applied at the compression edge of the beam. lef should be increased by 2h and may
be decreased by 0,5h for a load at the tension edge of the beam.
When a beam is supported against lateral torsional buckling (LTB) from the compressive edge and the beam is loaded from
the compressive side, the effective length
l
ef
in the design is the distance between the LTB supports a + 2h. When the beam is
loaded from the tensile side, the effective length
l
ef
=
a
- 0,5h. When the compressive edge of the beam is loaded only with
point loads at the locations of the LBT supports, the effective length lef = a
31
.
130
LVL Handbook Europe