The UK National Annex (NA) has reconsidered the partial factor system for piling recommended in EN 1997-1 Annex A in the light of concerns from the UK piling industry that the system does not reflect current UK practice. There are worries that Eurocode 7 might result in overly conservative or, in some instances, unsafe designs. The aim of the UK NA is to provide an equivalent level of safety to traditional good practice, taking into account the benefits of pile testing.
The table below shows the values of the partial factors in Set R4 that are recommended in the UK National Annex and compares these with values from EN 1997-1 and its earlier draft (ENV 1997-1). In addition, the National Annex sets all the resistance factors in set R1 to 1.0 for piles.
A key feature of the Nation Annex recommendations is the link between the values of the model (YRd) and resistance (yr) factors and the type and amount of pile testing performed on the site.
With no testing ('no explicit SLS check'), a design relies solely on calculation to guard against the occurrence of ultimate or serviceability limit states -there is no independent corroboration of either. Hence a high level of reliability is needed in the calculations.
With tests on working piles, verification of the ultimate limit state still relies on calculation alone. However, the piles' performance under serviceability conditions will be examined by the static load tests and, if found wanting, would lead to re-design of the piles. Hence lower partial factors can be tolerated than when no tests are performed.
Standard/type and MF*
amount of static -
load testing (where YRd applicable)
Partial resistance factors for Set R4|
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