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Steel Designers' Manual - 6th Edition (2003)
L/4
centroid of
deck profile
point load
—
compression
in concrete
____________________ tensi'e force
in decking
principal
crock
L L/4 cracked area interface
shear
Basic design 585
Fig. 20.5 Behaviour of composite deck slab as an equivalent reinforced concrete section
Fig. 20.6 Failure of composite slab by incomplete shear connection
system can only be readily assessed by testing. A typical composite slab under test
is shown in Fig. 20.7.
Mechanical interlock is partly dependent on the local plate stiffness and so indentations
are best situated close to the more rigid sections of the profile, such as
corners or narrow plate elements. Slippage is associated with separation; some profiles,
such as the dovetail section, achieve good shear-bond capacity by preventing
separation. Different trapezoidal profiles incorporate a wide variety of indent
and embossment shapes, as illustrated in Fig. 20.2, which have varying degrees of
effectiveness.
If design were to be carried out on elastic principles, permissible bond strengths
between the deck profile and the concrete would be of the order of 0.05 N/mm 2 for
plain profiles rising to about 0.2 N/mm 2 for some indented profiles. First slip and
flexural failure of plain trapezoidal profiles are coincident, whereas there is often a
considerable reserve following initial slip in properly designed composite slabs.
If failure of a composite slab that is propped during construction occurs by incomplete
shear connection, then the applied load to be considered in the analysis of its
shear bond strength is the imposed load plus self-weight loads on depropping. If the
slip