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Effective cross section size after 30 minutes fire exposure on all sides:
d_ef=β_n∙t+k_0∙d_0=0,70 mm/min∙30min+1,0∙7mm=28mm
Size of the effective cross section:
Width
b
: 133 mm - 2∙28 mm = 77 mm
Height
h
: 400 mm - 2∙28 mm = 344 mm
Beam properties of the effective cross section after 30min fire exposure:
Bending strength edgewise
f
m,0,edge,k
= 44 N/mm
2
Shear strength edgewise
f
v,0,edge,k
= 4,2 N/mm
2
Compression perpendicular to grain edgewise
f
c,90,edge,k
= 6 N/mm
2
Modulus of elasticity
E
0,k
= 11 600 N/mm
2
Modulus of rigidity
G
0,edge,mean
= 400 N/mm
2
Area of cross section
A
=
b∙h
= 26488 mm
2
Section modulus
W
y
=
b∙h
2
/6
= 1,52∙10
6
mm
3
Moment of inertia
I
y
=
b∙h
3
/12
= 2,61∙10
7
mm
4
Moment of inertia
I
z
=
h∙b
3
/12
= 1,31∙10
7
mm
4
Torsion moment of inertia
I
tor
= 0,3∙
h∙b
3
= 4,71∙10
7
mm
4
Modification factor
k
mod,fi
= 1,0
Modification factor
k
fi
= 1,1
Material safety factor
γ
M,fi
(default value in EC5)
= 1,0
Size effect factor
k
h
= (300/344)
0,15
= 0,98
9. CALCULATION EXAMPLES OF LVL STRUCTURES
c,90,d
=
c,90,d ef
=
c,90,d
∙ ( + 30 mm) =
15,2kN
150 mm ∙ (51 mm + 30 mm) = 1,3N/mm
2
k
c,90
is
1,4 for LVL-P flatwise and
f
c,90,k
is 2,2 N/mm
2
.
c,90
∙
c,90,flat,d
= 1,4 ∙ 1,1 1,2 ∙ 2,2 Nmm
2
= 2,8 N/mm
2
>
c,90,d
→ OK
ef
=
n
∙ +
0
∙
0
= 0,70 mmmin ∙ 30min + 1,0 ∙ 7mm = 28mm
9.11 MAIN BEAMOF ROOF STRUCTURE IN 30MIN FIRE EXPOSURE
Single-span main beam of a flat roof structure is GLVL 48 P beam 133x400 mm. Span length is L = 4000 mm,
width of the loading area 8000 mm and roof purlins are on the top of the beam. Support length is 100 mm.
Snow load sk is 2,5 kN/m
2
, own weight of the roof structure is 1,0 kN/m
2
and own weigh of the beam is
0,2 kN/m. The structure fulfils the ULS and SLS requirements in normal temperature where
w
net,fi
≤ L/300 has
been the most critical requirement. The re re istance R30 of the bea needs to be verified for fire exposure
on all sides of the beam.
LVL Handbook Europe
211