Connection of timber foundation piles to concrete extension piles

In this work, the relationship for a socket-type connection in wooden foundation piles is investigated, and a trilinear moment-rotation diagram was determined by means of experiment.
Numerical and analytical models confirmed that the material properties for compression perpendicular to the grain are governing for the connections’ strength and stiffness properties. This was similar to the response found in the experiment, where ductile behaviour was observed, which can be explained from the plasticization after the compression strength perpendicular was reached. Although because of the specific configuration (confined in a circular tube) the found strength perpendicular to the grain cannot be assigned to other configurations, a good estimation of the stiffness of the connection can be made with FEM models, assuming an MOE90 of 70 N/mm2 for a fully saturated pile. With a conservative assumption for the strength perpendicular to the grain the influence of the connection in a pile-soil model can be investigated also for other configurations than the tested one.
A procedure to study the influence of tangential (usually horizontal) soil displacements on timber piles with concrete extensions piles on top is proposed.
The outcome of a specific situation from practice with high horizontal loads showed that the bending capacity of the timber pile will in most cases be governing and not the investigated socket connection.