Mechanical Properties of Self-Compacting Concrete Filled Hollow Composite Steel Pipe Compression-Bending Members

Overview of the Study

The paper by Li Yongjin and Liao Feiyu, published in the Journal of Lanzhou University of Technology in 2012, presents a systematic experimental and numerical investigation into the mechanical behavior of compression-bending members composed of hollow composite steel tubes filled with self-compacting concrete (SCC). The research was supported by the National Natural Science Foundation of China (Grant No. 51108084). The study examined eight specimens varying in cross-sectional configuration, load eccentricity ratio, and concrete compressive strength. This work addresses a gap in the understanding of how self-compacting concrete, which eliminates the need for external vibration during placement, interacts with the hollow composite steel tube geometry under eccentric compressive loading.

Key Technical Parameters and Experimental Configuration

The experimental program was designed to isolate the influence of three primary variables on member performance. The cross-sectional form was varied to capture differences between solid and hollow composite geometries. Load eccentricity ratios were selected to span from near-axial to significantly eccentric loading conditions, simulating realistic structural scenarios. Concrete strength was varied across multiple grades to evaluate the composite action between the steel tube and the SCC infill.

Core Findings and Failure Modes

The experimental results demonstrated that the failure modes of hollow composite steel tube SCC compression-bending members closely resemble those of hollow composite steel tube members filled with conventional concrete. This finding is significant because it suggests that the self-compacting nature of the concrete does not fundamentally alter the failure mechanism. The primary failure mode involved local buckling of the steel tube wall at the region of maximum compressive stress, followed by crushing of the concrete core. The confinement provided by the hollow composite geometry effectively restrained lateral expansion of the concrete under compressive strain.

The numerical analysis employed a full-process finite element approach to trace the load-deformation relationship from initial loading through peak load to post-peak softening. A simplified analytical method was also developed for predicting member capacity, and the calculated results showed good agreement with experimental data. This validation provides confidence in the simplified method for practical engineering design applications.

Technical Insights and Engineering Implications

From a materials engineering perspective, the use of self-compacting concrete in confined steel tube members offers practical advantages in construction efficiency. SCC eliminates the need for compaction vibration, which is particularly beneficial in congested reinforcement zones and complex geometries where vibration equipment cannot be effectively applied. The hollow composite geometry provides a dual-confinement mechanism: the outer steel tube and the inner steel tube (forming the hollow chamber) both contribute to lateral restraint of the concrete core.

The finding that failure modes are similar to conventional concrete-filled members suggests that existing design provisions for steel tube concrete (STC) members can be adapted for SCC-filled configurations with appropriate modifications. The simplified calculation method developed in this study provides a practical tool for preliminary design, though engineers should verify critical members with full finite element analysis. The parametric study on eccentricity ratio is particularly valuable for engineers designing columns in frames subjected to moment demands from lateral loads such as wind or seismic forces.

Study Reflections

This research contributes to the growing body of knowledge on composite steel-concrete members and demonstrates that SCC is a viable infill material for hollow composite steel tube columns. The agreement between simplified analytical predictions and experimental results provides a foundation for incorporating these members into design codes. Future work should extend the investigation to include cyclic loading conditions to evaluate seismic performance, and to examine the long-term behavior under sustained loads including creep and shrinkage effects of the SCC.