Proceedings-DFI/EFFC 11th International Conference on Piling and Deep Foundations, 2014, Stockholm, Sweden, (DFI)
Buckling Resistance of Steel Micropiles with Mechanical Splices
Fredrik Sarvell, Ruukki Sverige AB, Sweden; Jukka Rantala, Ruukki Construction Oy, Finland; Veli-Matti Uotinen, Finnish Transport Agency, Finland; Harald Ihler, Ruukki Norge AS, Norway
Many of the valid international building codes state that the lateral support provided by the soil is sufficient to prevent buckling of fully embedded piles. However, the development of small diameter micropiles and especially the use of high strength steel have evolved to applications including high capacity elements. The ultimate structural load bearing capacity of a pile in a cohesive soil is decided by examining which gives the lowest value, the peak buckling load and the resisting moment provided by the surrounding soil medium or the structural capacity of the pile cross section. In both cases, the initial deflection of the pile is a significant factor when the axial load bearing capacity of the pile is determined. Steel micropiles are joined commonly with mechanical splices. A less rigid mechanical splice is often a weaker hinge that allows the pile to bend and deflect more during installation increasing the initial deflection of a pile. In addition the less rigid splice element decreases the bending capacity of a jointed pile section and the ultimate axial load capacity of the entire pile. A series of FE analysis performed for various pile sizes suggest that the steel pipe piles including separate pile sections and mechanical splicing elements should have the combined bending stiffness of EIshaft ≥ 0,75 × EIpile. This requirement yields to the buckling resistance of at least 96 % of the solid reference pile with the same initial eccentricity in similar soil conditions.
|article #1908; publication #100 (IC-2014)|