Zur Verwendung von Interaktionsdiagrammen beim Nachweis axial-zyklisch belasteter Pfähle

On the use of interaction diagrams for the design of axially cyclic loaded piles.

The need to take cyclic degradation of axially loaded piles into account was postulated in the DIN 1054:2005-01 for the first time in Germany. This lead to comprehensive research activities especially due to the progress in the offshore wind industry.
In the course of the scientific research the necessity for finding practical design approaches arose, which are capable to predict the behaviour under cyclic loading with sufficient accuracy, since the installation of offshore wind turbines already had started. This was the reason why the new chapter 13 and appendix D of the 2nd edition of the Recommendations of the Working Group 2.1 "Piles" of the German Geotechnical Society (EA-Pfähle, 2011) was published in advance in order to allow for the review of the engineering community.
In this chapter 13 an analysis format using cyclic interaction diagrams is given. These diagrams summarise practical experience with axially cyclic loaded piles and offer the assessment of an admissible number of load cycles depending on the cyclic loading and the static pile capacity.
In the paper at hand several cyclic interaction diagrams in use today are presented and their characteristics are discussed. The dominating effect on the cyclic degradation of a foundation pile for an offshore wind turbinde comes from a relatively high cyclic load ratio at a comparably low number of load cycles. This is the reason why a new modified cyclic interaction diagram is proposed, which takes into account this important effect in a realistic manner.
The use of interaction diagrams in line with the EA-Pfähle (2011) is explained and illustrated by practical examples. Finally a critical view on the applicability of the method in general is given.