Civil Engineering Reference
In-Depth Information
Figure 3.19
Definition of 'ductile' for welded studs, for steel
sections with equal flanges
Where partial shear connection is used and the connectors are 'ductile',
the bending resistance of cross-sections in Class 1 or 2 may be found by
plastic theory (Equation 3.66). Otherwise, elastic theory is required, which
is more complex and gives a lower resistance. Also, ductile connectors
may be spaced uniformly along a critical length whereas, for non-ductile
connectors, the spacing must be based on elastic analysis for longitudinal
shear.
These and other rules are intended to ensure that sudden longitudinal
shear failures do not occur; for example, by 'unzipping' of the shear
connection, commencing from a simply-supported end of a beam. There
is further explanation in Reference 17.
3.6.3
Transverse reinforcement
The reinforcing bars shown in Fig. 3.20 are longitudinal reinforcement for
the concrete slab, to enable it to span between the beam shown and those
on each side of it, but they also enhance the resistance to longitudinal
shear of vertical cross-sections such as B-B. Bars provided for that purpose
are known as 'transverse reinforcement', as their direction is transverse to
the axis of the composite beam. Like stirrups in the web of a reinforced
concrete T-beam, they supplement the shear strength of the concrete, and
their behaviour can be represented by a truss analogy.
The design rules for these bars are extensive, as account has to be taken
of many types and arrangements of shear connectors, of haunches, of the
use of precast or composite slabs, and of interaction between the longi-
tudinal shear stress on the section considered,
v
, and the transverse bending
moment, shown as
M
s
in Fig. 3.20. The loading on the slab also causes
vertical shear stress on surfaces such as B-B; but this is usually so much
less than the local longitudinal shear stress, that it can be neglected.
