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Talking Point with Dimitrios Selemetas

Eurocodes presents not only complexities for design but also the geotechnical software and the data it generates.

The introduction of Eurocodes has changed the format of pile loading information and the factors applied to calculate pile design resistances. As a result one of the biggest challenges for designers is the lack of consistency in loading information.

Typically, pile design information would be given in the form of a safe working load (SWL) per pile, which is only part of the information required for a fully compliant Eurocode design.

Indeed, in the realm of Eurocodes, it is possible for two piles carrying the same SWL to have different pile lengths depending on the proportion of dead and live load components. In accordance with the requirements of BS EN 1990 (Eurocode 0, Basis of Structural Design) the designer is required to apply different partial factors on permanent actions (Gk) and combinations of variable actions (Qk) to satisfy various ultimate limit states (ULS).

In cases, where the information is provided in the form of ULS pile loads, there appears to be a misconception that piles need to be designed against a unique ULS, without recognising that there are different ULS which govern different aspects of the pile design, such as length and reinforcement.

“It is important that we capture all the goodness of British Standards”

With the inherent complexity of Eurocodes in mind, it is not surprising that the demand for Eurocode soft ware that would speed up and simplify the design process has never been greater. Due to the increased volume and complexity of calculations required, the task of interrogating and checking soft ware output has similarly become more complex.

The extra complexity in calculations has introduced an extra reliance on software for design, which is not always followed by a good understanding of the fundamental principles behind the calculation engine.

Since pile design is quite a specialist area, most piling specialist contractors would typically make use of in-house design software capturing in-house knowledge and experience. This has meant that specialist piling contractors have invested heavily in upgrading their in-house design software and they would need to continue to do so in line with the future Eurocode evolution, which would add extra burden on design resources.

For those who have learned about pile design based on British Standards, this is clearly a turning point. As engineers are coming to terms with characteristic actions and serviceability limit states that correspond to 95% confidence levels, one cannot ignore the temptation of relying on previous well established practice and rules of thumb, resulting in a more liberal interpretation of the Eurocode rules.

As we continue with the transition from British Standards to Eurocodes, it is important that we capture all the goodness of British Standards, especially for future generations of engineers who will only learn how to design in terms of Eurocodes. I fear that if we keep complicating the design process further, the future of design capacity may only be measured in terms of gigabytes. 

Dimitrios Selemetas is a principal geotechnical engineer with Cementation Skanska.

 

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