Civil Engineering Reference
In-Depth Information
( c )
the actual stress must be less than the modifi ed design
strength [6.33]
k
n
is 4.5 for LVL, 5.0 for solid timber, 6.5 for glued laminated
timber
k1
k1
k1
1.5
k1+
1.1i
h
σ
m,
y,d
≤ k
crit
f
m,y, d
Note that for members such as roof beams subject to gravi-
tational actions with the top, compression edge laterally
restrained by decking, purlins, etc. (k
crit
= 1.0) wind suctions
may cause reversal of stress and compression on an unre-
strained bottom edge with k
crit
becoming critical.
For combined bending and compression expression [6.35]
must be met
k1
k1
k1
k1
k1
n
k1
n
k1
k=minimumof1or
k=
k=
X
h
1
2
h
1
α
−+8
0
[
1
−+
]
]
αα
[
αα
αα
.
1
αα
αα
α
−+
α
−+
−+
α
−+
−+
α
−+
−+
−+
−+
α
α
−
[6.62]
For a top notch (
Figure 19.10(b)
) k
v
= 1.00
Taking a rectangular section under notched LVL beam with
h
ef
=100, h = 150, x = 50,
l
= 0 so
α
= 0.67 and k
n
= 4.5 for
LVL then
from [6.62] k
v
= min. 1.0 or
2
σ
σ
d
σ
0,d
σ
m,
σ
σ
c,
c,
m,
d
+
c,
c,0,
0,d
d
≤
1.0
k
crit
f
m,
k
c,z
f
c,
d
0,d
f
m,
f
c,
45
4
45
049
where k
c,z
is given by [6.26].
=
0
04
50
150
1
067
2
150 0671 0
67
08
0
.(
0671
.(
.
71 .)
0
.)
0670
.
70
.)
0
.)
0670
.
7 .
067
−
06
0.)
.)
0
.)
06
0
.)
0670
.
70
70
.
70×
70
−
0
06
19.5.5 Shear
Concentrated loads closer to the support than the effective
depth of the member can be ignored for shear but not for bear-
ing at the support. The breadth of a shear section has to modi-
fi ed by k
cr
= 0.67 (UK NA Table NA.4) for solid timber and
glulam otherwise k
cr
= 1.0. In a full rectangular cross-section
of solid timber or glulam the shear stress is given by
Maximum shear strength is 0.49 f
v,d
with the shear stress =
1.5 V / (k
cr
× b × h
ef
).
0
06
19.5.6 Compression perpendicular to grain
To compensate for the low characteristic value for compression
perpendicular to grain, the breadth of bearing is increased by
30 mm in a direction parallel to the grain where this dimension
is available (see
Figure 19.11
) to give an effective bearing area
A
ef
.
1.V
1
.V
15
k
b h
[cl. 6.1.7].
EC5-1-1 cl. 6.5.2 gives the shear strength reduction for both
over and under notched ends in solid timber, glulam and LVL
(
Figure 19.10
).
For beams notched on the same side as the support
(
Figure 19.9(a)
) (under notch)
cr
In addition, the design strength f
c, 90, d
can be increased by the
factor k
c,90
. EC5 is not clear on the values that may be ascribed
to k
c,90
. Together with the values given in PD 6693-1 k
c,90 m
ay
be taken as:
i is the notch inclination; for a 90
o
notch i = 0
(i) bearing of beams, joists and similar members
1.50 for softwood
1.75 for softwood glued laminated timber
(ii) studs bearing on a continuously supported plate
h is the beam depth
h
ef
is the effective depth
x is the distance from the line of action of the support reaction to
the corner of the notch
1.25 for softwood plate
α
=
h
h
ef
1.50 for softwood glulam plate
x
iii h-h
h-
h
h-
ef
)
ef
)
(a)
(b)
Figure 19.10 End notched beams (BSI, 2004). Permission to reproduce extracts from BS EN 1995-1-1 is granted by BSI
