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Steel Designers' Manual - 6th Edition (2003)
deck
(a) (b)
overlap
The normal method of designing simply-supported beams for strength is by plastic
analysis of the cross-section. Full shear connection means that sufficient shearconnectors
are provided to develop the full plastic capacity of the section. Beams
designed for full shear connection result in the lightest beam size. Where fewer
shear-connectors are provided (known as partial shear connection) the beam size is
heavier, but the overall design may be more economic.
Partial shear connection is most attractive where the number of shear-connectors
is placed in a standard pattern, such as one per deck trough or one per alternate
trough where profiled decking is used. In such cases, the resistance of the shearconnectors
is a fixed quantity irrespective of the size of the beam or slab.
Conventional elastic design of the section results in heavier beams than with
plastic design because it is not possible to develop the full tensile resistance of the
steel section. Designs based on elastic principles are to be used where the
compressive elements of the section are non-compact or slender, as defined in
BS 5950 Part 1. This mainly affects the design of continuous beams (see section
21.6.3).
21.3 Guidance on span-to-depth ratios
Guidance on span-to-depth ratios 603
Fig. 21.3 Composite beams incorporating composite deck slabs: (a) deck perpendicular to
beam, (b) deck parallel to beam
Beams are usually designed to be unpropped during construction. Therefore, the
steel beam is sized first to support the self-weight of the slab before the concrete
has gained adequate strength for composite action. Beams are assumed to be laterally
restrained by the decking in cases where the decking crosses the beams (at
an angle of at least 45° to the beam) and is directly attached to them. These beams
can develop their full flexural capacity.
Where simply-supported unpropped composite beams are sized on the basis of
their plastic capacity it is normally found that span-to-depth ratios can be in the