Hysteretic Performance of Pre-stressed Hollow Sandwich Steel Tube Concrete Members Under Tensile-Compressive Cycles

Literature Overview

This study investigates the cyclic tensile-compressive hysteretic behavior of pre-stressed hollow sandwich steel tube concrete (HSTC) members, a novel composite structural system that combines the advantages of steel tube confinement with the compressive strength of concrete while maintaining structural lightness. The research is particularly significant given the growing demand for high-performance structural components in seismic-resistant design, where energy dissipation capacity under repeated loading becomes a critical design parameter. The authors conducted full-scale cyclic loading tests on specimens incorporating pre-stress through external tendons or internal prestressing systems, which is a departure from conventional HSTC members that rely solely on passive confinement.

Core Technical Content and Test Methodology

The experimental program involved the fabrication of hollow sandwich steel tube concrete specimens with varying pre-stress levels and geometric configurations. The hollow sandwich configuration typically consists of an outer steel tube and an inner steel tube with concrete placed in the annular space between them, or in some configurations, the inner tube itself serves as a prestressing element. The cyclic loading protocol followed standard seismic testing procedures, applying displacement-controlled reverse cyclic loading to capture the complete load-deformation response through multiple loading-unloading cycles.

The pre-stress application method is a distinguishing feature of this research. By introducing controlled pre-stress before the cyclic loading phase, the authors aimed to evaluate whether initial compressive stresses in the concrete core could delay cracking, reduce residual deformations between cycles, and ultimately improve the overall energy dissipation capacity. The specimens were instrumented with strain gauges on both the outer and inner steel tubes, along with displacement transducers to record the full hysteretic loops.

Key Findings and Technical Insights

The study demonstrates that pre-stress significantly enhances the hysteretic performance of HSTC members. The pre-stressed specimens exhibited larger enclosed areas in the load-displacement hysteresis loops compared to non-pre-stressed counterparts, indicating superior energy dissipation. The pre-stress effectively counteracted tensile stresses induced during the tension phase of cyclic loading, thereby delaying the onset of concrete cracking and steel tube yielding.

The degradation rate of stiffness under repeated loading was reduced in pre-stressed specimens. This finding is particularly valuable for engineers designing structures in high-seismicity zones, where maintaining structural integrity through multiple loading cycles is essential. The research also reveals that the pre-stress level has an optimal range — excessive pre-stress can lead to premature local buckling of the inner tube under compressive cycles, which is a critical design consideration that the study addresses through parametric analysis.

Engineering Practice Implications

From a welding and fabrication perspective, the introduction of pre-stressing systems into HSTC members adds complexity to the manufacturing process. The connection details between the prestressing tendons and the steel tube require careful welding design to avoid stress concentrations at weld toes. Engineers should pay particular attention to the weld quality at tendon anchorage points, where cyclic loading will impose repeated stress reversals. Post-weld heat treatment or peening of these critical welds is recommended to mitigate fatigue risks.

Study Insights and Reflections

This research represents a meaningful advancement in the understanding of composite steel-concrete structural systems. The concept of active pre-stress in HSTC members bridges the gap between traditional prestressed concrete design philosophy and modern steel-concrete composite engineering. However, I note that the practical implementation challenges — particularly regarding tendon corrosion protection in the annular concrete zone and long-term pre-stress loss due to concrete creep and shrinkage — deserve further investigation. The cyclic performance data presented in this study provides a solid foundation for developing design guidelines, but the transition from laboratory-scale validation to full-scale structural application requires additional research on durability and long-term behavior under combined environmental and mechanical loading.