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Steel Designers' Manual - 6th Edition (2003)
872 Steel piles
Tubular piles are available in a wide variety of sizes, and both Larssen and
Frodingham sheet piles are suitable as infill piles. Appropriate clutches are welded
to the walls of the tubes, and these provide the designer with simple corner details
for many different wall angles. It is apparent that the clutch locking bar strips from
U-section sheet piles (or Larssen sections) are more stable to weld onto the tubulars
than those from Frodingham section sheet piles.
29.1.3 Design
29.1.3.1 Design basis
The basis of design of any bearing pile is its ultimate axial capacity in the particular
soil conditions at the site where the structure is to be built. The design resistance
is determined from the ultimate capacity, and the designer verifies that this is adequate
to carry the required loads from the structure.
Until recently, design resistance of foundations has been evaluated on an allowable
stress basis. However, structural design is now using a limit state design (LSD)
basis, whereby partial factors are applied to various elements of the design according
to the reliability of the method and of the soil properties. However, the application
of limit state design philosophy to geotechnical design is causing difficulty in
a discipline where the allowable stress approach and terms such as the ‘allowable
bearing pressure’, ‘permissible steel stress’, and ‘allowable pile capacity’ are widely
accepted and understood. Nevertheless, the LSD approach is being progressively
adopted in the British Standards as they are revised, and is the basis for all the
Eurocodes, 3 including that for foundation design.
29.1.3.2 Design standards
The common design standard used for the design of bearing piles is the offshore
industry’s recommended practice for steel tubular piles, based on US and UK North
Sea experience, which is contained in the American Petroleum Institute Code RP
2A (API RP2A) 4 that will be adopted in the ISO Code 13819-2. 5
A draft of the new Eurocode 7: Part 1 6 has recently been produced after several
years of effort by an eminent team, and the UK pre-standard DD-ENV 1997-1 7 with
the National Application Document (NAD), was published in July 1995. It presents
a more rigorous treatment of limit state design (LSD) than any of the British Standards
relating to foundations so far. Allowable stress design (ASD) is still, however,
permitted in BS 8002 8 and BS 6349, 9 in order to be compatible with the approach
taken in BS 449. 10
Further information can be obtained from the SCI publication Steel Bearing Piles
Guide. 11