Civil Engineering Reference
In-Depth Information
ρ
=
(
ρ
x
ρ
y
)
1/2
≤
0.02
and the design shear stress as
v
Rd
=
(0.18/
γ
C
)[1
+
(200/
d
)
1/ 2
](100
ρ
f
ck
)
1/3
≥
v
min
(3.23)
where:
v
min
is given by Equation 3.21,
d
is the mean of the effective depths of the two layers of reinforcement,
but not less than 200 mm,
γ
C
has the recommended value 1.50, and the units are as for Equation 3.21.
The punching shear resistance is
V
Rd
=
v
Rd
c
p
d
(3.24)
It is not clear from EN 1994-1-1 whether account can be taken of contri-
butions from the concrete ribs and the sheeting. None has been assumed
here, so Equation 3.24 is likely to give a conservative result.
3.3.5
Bending moments from concentrated point and line loads
Since composite slabs span in one direction only, their ability to carry
masonry partition walls or other heavy local loads is limited. Rules are
given in EN 1994-1-1 (and in the British code) for widths of composite
slabs effective for bending and vertical shear resistance, for point and line
loads, as functions of the shape and size of the loaded area. These are
based on a mixture of simplified analyses, test data and experience.
Where transverse reinforcement is provided with a cross-sectional area
of at least 0.2% of the area of concrete above the ribs of the sheeting, no
calculations are needed for characteristic concentrated loads not exceed-
ing 7.5 kN.
The rules for use where this simplification does not apply are now
explained, with reference to a rectangular loaded area
a
p
by
b
p
, with its
centre distance
L
p
from the nearer support of a slab of span
L
, as shown in
Fig. 3.6(a). The load may be assumed to be distributed over a width
b
m
,
defined by lines at 45° (Fig. 3.6(b)), where
b
m
=
b
p
+
2(
h
f
+
h
c
)
(3.25a)
and
h
f
is the thickness of finishes, if any. The code does not refer to
distribution in the spanwise direction, but it would be reasonable to use
the same rule, and take the loaded length as
