Experimental investigation and development of design equation for circular hollow precast high-strength concrete-filled steel tube piles under uniaxial compressive loading

This study investigates the structural performance of circular hollow precast high-strength concrete-filled steel tube (H-HSCFST) piles under uniaxial compressive loading through extensive experimentation and development of novel design equations. The research tested 30 H-HSCFST specimens, varying critical parameters, including concrete compressive strength (up to 130 MPa), steel yield strength (up to 447 MPa), steel tube thickness, and concrete shell thickness. For the first time, uniaxial compression capacity tests were conducted for H-HSCFST specimens with concrete infill to clarify their contributions to compressive capacity. These experiments significantly expand the existing hollow concrete-filled steel tube (H-CFST) database, particularly in the high-strength concrete range. Findings revealed that parametric evaluation of the H-HSCFST database shows that the experimental-to-calculated capacity ratio is inversely related to concrete compressive strength, diameter-to-thickness ratios, and hollowness ratio, but positively correlated with steel yield strength. Furthermore, the presence and loading condition of concrete infill significantly influenced performance, with load-bearing infill enhancing post-peak ductility—a crucial consideration for seismic design applications. The study further exposed limitations in current design methods, particularly their inability to capture the decreasing capacity ratio trend with increasing concrete strength. In response, novel design equations were proposed, incorporating modification factors for steel and concrete derived from experimental database, considering composite stress states and parametric effects. These equations exhibited improved predictive performance, achieving an R-squared value of 0.90. A modification factor for load-bearing concrete infill was also introduced. This research provides essential tools for engineers designing high-performance H-HSCFST piles, enabling more accurate and reliable compressive capacity predictions. • Investigated 30 H-HSCFST pile specimens with concrete strength up to 130 MPa. • First tests on compressive capacity of H-HSCFST with concrete infill. • Exposed limitations in current design methods for HSC applications. • Proposed new compressive capacity equations, achieving R 2 of 0.90 in predictions. • Developed compressive capacity eq. for H-HSCFST with load-bearing concrete infill.