Hysteresis Behavior of Prestressed Hollow Sandwich Steel Tube Concrete Members under Tension and Compression

Literature Overview

This paper investigates the cyclic tensile-compressive hysteresis behavior of prestressed hollow sandwich steel tube concrete (HSCC) members through quasi-static loading experiments. The research addresses a critical gap in the seismic design of composite structural members, particularly those employed in high-rise buildings and bridge piers where ductility and energy dissipation are paramount. The hollow sandwich configuration combines an outer steel tube, an inner steel tube, and a concrete core, with prestressing applied to enhance initial stiffness and delay cracking under cyclic loading. The study provides valuable data for engineers designing composite members subjected to reversed cyclic loads, such as those encountered during seismic events.

Core Technical Content and Key Findings

The experimental program involved specimens with varying prestress levels and geometric parameters. The prestressed hollow sandwich steel tube concrete members demonstrated significantly improved hysteretic performance compared to conventional filled steel tube concrete members. The key observations include the following:

• The prestress application effectively increased the initial stiffness and delayed the onset of concrete cracking under tension.
• Under cyclic compression, the hollow sandwich configuration provided superior confinement to the concrete core, resulting in enhanced ductility and energy dissipation capacity.
• The hysteresis loops exhibited stable and full shapes with minimal pinching, indicating good energy absorption characteristics throughout the loading cycles.
• The ultimate displacement ductility ratio increased with higher prestress levels, though excessive prestress led to brittle failure modes in some specimens.

Typical Test Parameters

Defect and Failure Analysis

The failure modes observed during testing followed a progressive pattern. Initial micro-cracking occurred at the concrete-concrete interface and at the steel tube weld seams under tension. As loading progressed, the outer tube experienced local buckling under compression, while the inner tube provided additional confinement. The weld connections between the outer and inner tubes were identified as potential weak links, with some specimens showing weld cracking at high displacement amplitudes. Engineers should pay close attention to the weld quality at the interface between the inner and outer tubes, as inadequate weld penetration or porosity can significantly reduce the effective composite action.

Engineering Practice Implications

From a practical standpoint, the prestressed hollow sandwich configuration offers a viable solution for retrofitting existing steel tube concrete members in seismic zones. The prestress can be applied using high-strength tendons embedded within the hollow space between the inner and outer tubes. However, the construction complexity increases significantly, requiring precise alignment of the inner tube, careful placement of prestressing tendons, and controlled grouting of the concrete core. The welding of the inner tube to the outer tube must comply with stringent quality standards, and post-weld heat treatment may be necessary for higher-grade steels to relieve residual stresses.

The study also highlights the importance of considering the interaction between prestress relaxation and cyclic loading. Over multiple loading cycles, the prestress level may decrease due to concrete creep and steel stress relaxation, which could affect the long-term performance of the member. Engineers should incorporate prestress loss factors into their design calculations, particularly for members subjected to frequent seismic events or thermal cycling.

Study Insights and Conclusions

This research contributes meaningfully to the understanding of composite member behavior under cyclic loading. The prestressed hollow sandwich concept demonstrates promise for applications requiring both high stiffness and excellent ductility. However, further research is needed on the long-term durability of the prestressing system, the effect of corrosion on the inner tube, and the feasibility of large-scale implementation. Engineers working on seismic design of composite structures should consider this configuration as a potential alternative to conventional steel tube concrete members, particularly where space constraints or weight limitations preclude the use of larger diameter tubes.