Analysis of bond performance between square hollow steel tubes and UHTCC interfaces

Abstract

This study investigates the bond performance at the interface between square hollow steel tubes and ultra-high-toughness cementitious composites (UHTCC). Specimens with varying slenderness and width-to-thickness ratios were evaluated using push-out tests. The study analyses damage patterns, longitudinal strain distribution curves, load–slip curves, bonding mechanisms, interfacial bond strength distribution, and microstructure. The results indicate that bond-slip failure occurs at the bonding interface of the steel tube and UHTCC. Strain curve demonstrates an exponential decrease along the length of the specimen, and the load–slip curve reveals the stages of bonding, slip, and friction. The bond strength initially increases and subsequently decreases as the slenderness ratio increases. Conversely, it decreases as the width-to-thickness ratio increases. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were utilised to investigate microstructure. A finite element model was constructed for the composite structure, in which the stress distribution patterns and load–slip behaviour of the steel tube exhibited strong consistency with the test results. A bond strength distribution equation for the interface was derived, along with fitting equations with respect to bond strength and load. To extend the findings, a finite element model was constructed under linear elasticity to investigate interfacial changes. This study provides a solid theoretical foundation for designing square hollow steel tube–UHTCC composite structures.