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Steel Designers' Manual - 6th Edition (2003)
than concrete piles and either the load supported can be greater or the size of the
group made smaller. The stiffness of H-piles is different about each orthogonal axis,
allowing designers to select the orientation necessary to achieve the most efficient
design.
H-piles are used principally for terrestrial structures where the full length of the
pile is embedded, e.g. foundations for bridges and buildings, and therefore buckling
is not a problem because there is good soil lateral support.They are used very effectively
to transfer bearing loads into buried bedrock and to get around buried
obstructions. It is sometimes advisable to use special cast steel pile shoes to
strengthen the tip and prevent damage or buckling under hard driving conditions
into bedrock where very high end bearing pressure can be achieved.
They are generally not the most suitable for conditions where long lengths of the
pile shaft protrude above ground level and are unsupported by surrounding soil or
through water, because buckling failure about the minor axis can occur at relatively
low axial loads. In these cases consider the use of tubular or box piles that have
more stiffness.
29.1.2.2 Tubular piles
Bearing piles 869
Tubular piles were first used as foundations for offshore oil platforms in the oil fields
of Lake Maracaibo in Venezuela in the 1920s. Initially, spare oil pipe was used out
of convenience but, as the supporting structures became more sophisticated, the
cold rolling of piles in structural plate to project-specific diameters and wall thicknesses
became more common.
Purpose-rolled tubular piles can be used, but high quality steel line pipe is perfectly
suitable for piling. Tubular piles are available in a large range of diameters
and wall thicknesses. Typical sections used for piling purposes are produced as line
pipe to API 5 L grades X52 (yield stress of 52 ksi, approximately equal to 355 N/mm 2 )
to X80 (yield stress of 80 ksi, approximately equal to 555 N/mm 2 ). 2 Tubular sections
can be hot- or cold-rolled. The cold-rolling process produces consistently higher
yield strengths than those of hot-rolled steel products and this can have significant
benefits for highly loaded bearing pile and structural column-pile applications, and
can also permit harder driving.
Steel tubular piles have a high stiffness and are therefore also suitable for sites
where it is necessary to transfer bearing loads into buried bedrock. They are particularly
suitable for marine structures, especially where sited in deep water, e.g.
berthing jetties for deep draught vessels. Increasing use is being made of steel tubulars
in composite columns for buildings and bridges where the tube is first driven
as a pile before filling the upstand above ground level with a reinforced concrete
core for added strength and rigidity. This permits significant savings in cost due to
faster construction. More applications will become possible as the results of research
into the effects of pile driving, dynamic load testing, corrosion, and new coatings are
analysed and reported to design engineers.