Structural performance of circular hollow precast high-strength concrete-filled steel tube piles under cyclic flexural and varying high axial loads

Abstract

This paper investigates the structural performance of hollow precast high-strength concrete-filled steel tube (H-HSCFST) piles under cyclic flexural and varying high axial loads, simulating severe seismic conditions. An experimental program on eight real-scale specimens was conducted to examine the influence of steel tube thickness, concrete shell thickness, and the presence of concrete infill on the capacity and the ductility of the H-HSCFSTs. The investigation showed that ductility is significantly enhanced by using compact steel tubes and concrete infill, while thick concrete shell enhanced the moment capacity, whereas noncompact tubes combined with thin concrete shells exhibit poor performance. Furthermore, the results found that existing design codes (AISC 360–22, AIJ 2022 guideline on foundation members, and Eurocode 4) are inadequate for predicting pile behavior under these demanding loads. Recommendations to update these existing codes were suggested. To address the identified modeling deficiencies, a computationally efficient multi-spring fiber-based numerical model was developed. This model incorporates novel constitutive laws where new coefficients are proposed for both the steel and concrete material models to directly reflect the observed experimental phenomena. The modified steel model uses these coefficients to account for strength loss after concrete crushing, while the concrete model uses them to correlate strength and residual stress to shell slenderness. Comparison against experimental data demonstrated that the proposed model accurately reproduces the global moment-drift responses and local strain distributions. Furthermore, the model was successfully validated against 11 specimens from an independent dataset. The developed model provides an efficient and reliable tool for the seismic design of H-HSCFST piles for engineering practice.