Abstract
This study presents a numerical investigation into the structural behavior of a pile-in-pile (PIP) slip joint utilizing square hollow section (SHS) members, with a comparative assessment against conventional circular hollow sections (CHSs). A comprehensive finite element model was developed and validated against published CHS experimental results to evaluate key performance indicators, including stress distribution, buckling behavior, and load-carrying capacity under pure bending, axial compression, and diagonal lateral loads. The analysis revealed that SHS joints demonstrated distinct stress concentration patterns and higher capacity under axial compression, whereas CHS joints provided superior performance under bending due to their geometric symmetry. However, SHS corners were more vulnerable under diagonal loading, exhibiting localized buckling at relatively lower loads. These structural weaknesses can be mitigated through design improvements, such as increased wall thickness or corner strengthening. The findings highlight that while SHSs introduce certain vulnerabilities compared to CHSs, they also offer advantages in axial load resistance, supporting their potential as a viable alternative for offshore wind foundation connections.