Thermal stress analysis of energy piles

This study is concerned with the problem of energy piles subjected to constant axial load and temperature variation uniform over the cross-section. In the first part of this paper, equations for the analysis of energy piles based on elastic theory and the load-transfer approach are described. Closed-form solutions are derived for a few simple cases. It is observed that temperature variation effects can be conveniently expressed by a factor of thermally imposed strain. In the second part of the paper, a study on the effect of the non-linearity of reinforced concrete on the performance of energy piles under tension is described. A newly developed finite-element model that is within the framework of the load-transfer approach is employed to simulate the response of a pile subjected to thermomechanical loads in isolated as well as in piled raft foundations. The results suggest that the performance of the structure is strongly affected by concrete post-cracking behaviour. Nevertheless, piles can accommodate thermally imposed strains if the ductility capacity is provided. The outcomes of this study may be combined with the knowledge of non-linear behaviour of soil-pile interfaces for a more rational performance-based design approach toward energy piles.