Steel Designers Manual - TheBestFriend.org

This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007
To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/
Steel Designers' Manual - 6th Edition (2003)
21.4 Types of shear connection
The modern form of shear-connector is the welded headed stud ranging in diameter
from 13 to 25 mm and from 65 to 125 mm in height. The most popular size is 19 mm
diameter and 100 mm height before welding. When used with steel decking, studs
are often welded through the decking using a hand tool connected via a control unit
to a power generator. Each stud takes only a few seconds to weld in place. Alternatively,
the studs can be welded directly to the steel beams in the factory and the
decking butted up to or slotted over the studs.
There are, however, some limitations to through-deck welding: the top flange of
the beam must not be painted, the galvanized steel should be less than around
1.25 mm thick, the deck should be clean and free of moisture, and there should be
no gap between the underside of the decking and the top of the beam.The minimum
flange thickness must not be less than the diameter of the stud divided by 2.5
(typically, 19/2.5 = 7.6 mm). The power generator needs 415 V electrical supply, and
the maximum cable length between the weld gun and the power control units should
be limited to around 70 m to avoid loss of power. Currently, only 13, 16 or 19 mm
diameter studs can be through-deck welded on site.
Where precast concrete planks are used, the positions of the shear-connectors are
usually such that they project through holes in the slab which are later filled with
concrete. Alternatively, a gap is left between the ends of the units sitting on the top
flange of the beam on to which the shear connectors are fixed. Reinforcement
(usually in the form of looped bars) is provided around the shear-connectors.
There is a range of other forms of welded shear-connector, but most lack practical
applications. The ‘bar and hoop’ and ‘channel’ welded shear-connectors have
been use in bridge construction. 5 Shot-fired shear-connectors may be used in smaller
building projects where site power might be a problem. All shear-connectors should
be capable of resisting uplift forces; hence the use of headed rather than plain studs.
The number of shear-connectors placed along the beam is usually sufficient to
develop the full flexural resistance of the member. However it is possible to reduce
the number of shear-connectors in cases where the moment resistance exceeds the
applied moment and the shear-connectors have adequate ductility (or deformation
capacity). This is known as partial shear connection and is covered in section 21.7.4.
21.5 Span conditions
Span conditions 605
In buildings, composite beams are usually designed to be simply-supported, mainly
to simplify the design process, to reduce the complexity of the beam-to-column connections,
and to minimize the amount of slab reinforcement and shear-connectors
that are needed to develop continuity at the ultimate limit state.
However, there are ways in which continuity can be readily introduced, in order
to improve the stiffness of composite beams. Figure 21.5 shows how a typical connection
detail at an internal column can be modified to develop continuity. The stub