Civil Engineering Reference
In-Depth Information
2.8
Longitudinal shear in composite slabs
There are three types of shear connection between a profiled steel sheet
and a concrete slab. At first, reliance was placed on the natural bond
between the two. This is unreliable unless separation at the interface
('uplift') is prevented, so sheets with re-entrant profiles, such as Holorib,
were developed. This type of shear connection is known as 'frictional
interlock'. The second type is 'mechanical interlock', provided by press-
ing dimples or ribs (Fig. 2.8) into the sheet. The effectiveness of these
embossments depends entirely on their depth, which must be accurately
controlled during manufacture. The third type of shear connection is 'end
anchorage'. This can be provided where the end of a sheet rests on a steel
beam, by means of shot-fired pins, or by welding studs through the sheeting
to the steel flange.
2.8.1
The m-k or shear-bond test
The effectiveness of shear connection is studied by means of loading tests
on simply-supported composite slabs, as sketched in Fig. 2.19. Specifica-
tions for such tests are given in clause B.3 of EN 1994-1-1. The length of
each shear span,
L
s
, is usually
L
/4, where
L
is the span, which is typically
about 3.0 m. There are three possible modes of failure:
•
in flexure, at a cross-section such as 1-1 in Fig. 2.19,
•
in longitudinal shear, along a length such as 2-2, and
•
in vertical shear, at a cross-section such as 3-3.
The expected mode of failure in a test depends on the ratio of
L
s
to the effective depth
d
p
of the slab, shown in Fig. 2.20. In tests to EN
1994-1-1, the results are plotted on a diagram with axes
V
/
bd
p
and
A
p
/
bL
s
(Fig. 2.21), for reasons that are now explained.
At high
L
s
/
d
p
, flexural failure occurs. The maximum bending moment,
M
u
, is given by
Figure 2.19
Critical sections for a composite slab
