The design of cylindrical tubes in piling systems has to consider the limit state of buckling. The application of the general rules for buckling design given in ENV1993-1-6 results in insufficient safety factors for common piling structures. This is due to the fact that the knockdown factors of ENV1993- 1-6 are derived from tests with rigid boundary conditions and a load introduction, which is completely different from the situation with the piling structure.
The continuous non-linear support in the soil reduces the imperfection sensitivity. A parametric study considering the interaction of piling and soil will be performed to give improved design rules with satisfactory safety.