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Steel Designers' Manual - 6th Edition (2003)
Chapter 27
Foundations and
holding-down systems
by HUBERT BARBER
27.1 Foundations
27.1.1 Types of foundation
Pad foundations are used primarily to support the major structural elements in
either sheds or multi-storey buildings. The pad foundations to major elements may
be either mass concrete or reinforced concrete, the latter when either heavy loads
or very poor ground conditions are present. They may be used in the context of
cladding to support intermediate posts carrying sheeting rails, in which case the load
is almost all from wind forces and is horizontal.
Strip foundations are used in steel-framed buildings to support external masonry
or brickwork cladding and masonry internal partitions. In some cases the ground
floor is thickened at these locations to provide a foundation but care should be taken
with respect to the appropriate depth for clay or frost heave and for compatibility
between such foundations and those of the main frame.
Piled foundations, either driven, bored or cast in place, are used on sites where
ground conditions are poor or for buildings or structures in which differential settlement
is critical. They may also be required in circumstances where heavy concentrations
of load occur. In general when piled foundations are used the whole of
the construction should be supported on piles. The ground floor slab, ground floor
cladding and internal partitions should be carried by ground beams between the
pile cap locations. If it is necessary for reasons of economy to support the ground
floor independently, provision should be made for differential settlement by the
inclusion of suitable movement joints.
Ground improvement techniques are appropriate for some types of poor ground.
The most usual techniques are vibro-compaction or vibro-replacement but dynamic
compaction can also be useful for improvement of large isolated sites. Ground
improvement specialists or specialist consultants should be approached as economy
will be the most important factor in the decision.
Typical foundation layouts are shown in Fig. 27.1.
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