Civil Engineering Reference
In-Depth Information
Figure 3.18
Vertical shear in a beam with an off-centre point load
has a heavy point load at B. The critical sections are A, B and C. The total
number of connectors is shared between lengths AB and BC in proportion
to the areas of the shear force diagram, OEFH and GJH.
In practice it might be necessary to provide a few extra connectors
along BC, because codes limit the maximum spacing of connectors to
prevent uplift of the slab relative to the steel beam, and to ensure that the
steel top flange is sufficiently restrained from local and lateral buckling.
3.6.2
Ductile and non-ductile connectors
The use of uniform spacing is possible because all connectors have some
ductility, or
slip capacity
. Its determination from push tests is explained in
Section 2.5.
The slip capacity of headed stud connectors increases with the diameter
of the shank, and has been found to be about 6 mm [33] for 19-mm studs
in solid concrete slabs. Higher values have been found in tests with single
studs placed centrally within the troughs of profiled steel sheeting. Off-
centre studs in troughs can be much less ductile.
Slip enables longitudinal shear to be redistributed between the connec-
tors in a critical length, before any of them fail. The slip required for this
purpose increases at low degrees of shear connection, and as the critical
length increases (a scale effect). A connector that is 'ductile' (has sufficient
slip capacity) for a short span becomes 'non-ductile' in a long span, for
which a more conservative design method must be used.
The definitions of 'ductile' connectors given in EN 1994-1-1 for headed
studs welded to a steel beam with equal flanges and S355 steel are shown
in Fig. 3.19. The more liberal definition given by the dashed line, for use
where the slab is composite, is subject to several restrictions, based on the
limited scope of current research data on slip capacity.
No design data are given in EN 1994-1-1 for shear connectors other
than headed studs. If used, they should be treated as non-ductile unless
their characteristic slip capacity is at least 6 mm.
