Bending Performance and Finite Element Analysis of Square Hollow Sandwich Steel Tube Concrete Composite Members

Literature Overview

This research investigates the bending performance of square hollow sandwich steel tube concrete (HSCC) composite members through experimental testing and finite element analysis (FEA). Square HSCC members offer advantages over circular counterparts in terms of space utilization and connection detailing, making them attractive for building frames and bridge cross-beams. The hollow sandwich configuration provides enhanced confinement to the concrete core while maintaining a relatively lightweight section.

Core Technical Content and Key Findings

The experimental program involved square HSCC specimens with varying inner tube sizes, concrete grades, and steel grades. The specimens were subjected to four-point bending under monotonic loading, with displacement and strain measurements taken at multiple locations. The FEA models were validated against experimental results, demonstrating good agreement in load-deflection curves and failure modes.

Specimen Configuration and Material Properties

Bending Performance Characteristics

The bending capacity of the square HSCC members was found to be 15–25% higher than that of solid filled steel tube concrete members of equivalent cross-sectional area. This improvement is attributed to the enhanced confinement effect provided by the inner tube on the concrete core. The failure mode typically involved local buckling of the outer tube followed by concrete crushing in the compression zone. The inner tube played a crucial role in maintaining the integrity of the concrete core even after the outer tube had buckled.

The FEA analysis revealed that the stress distribution in the concrete core was highly non-uniform, with the highest compressive stresses occurring near the inner tube. The concrete between the inner and outer tubes experienced a triaxial stress state, which significantly enhanced its compressive strength. The FEA also showed that the weld connections between the inner and outer tubes experienced significant shear stresses, which could be a potential failure initiation point.

FEA Model Validation

Engineering Practice Implications

The study provides valuable design guidance for engineers considering square HSCC members in structural applications. The enhanced bending capacity and ductility make these members suitable for seismic design, where energy dissipation and ductility are critical. However, the connection design between the inner and outer tubes requires careful attention, as the shear stresses at the welds can lead to premature failure if not properly addressed. Engineers should consider using fillet welds with adequate leg size and possibly adding stiffener plates at critical locations to distribute the shear stresses.

The FEA model developed in this study can be adapted for parametric analysis to optimize the geometric proportions of the inner and outer tubes for specific loading conditions. Engineers are encouraged to use the validated FEA model as a starting point for their own design studies, modifying the material properties and boundary conditions to suit their specific applications.

Study Insights and Conclusions

This research demonstrates that square hollow sandwich steel tube concrete members offer a promising alternative to conventional composite members for bending applications. The combination of experimental validation and FEA analysis provides a comprehensive understanding of the structural behavior and failure mechanisms. Engineers should leverage these findings in the design of building frames, bridge cross-beams, and other structural elements where bending is the dominant loading mode. Future research should focus on the long-term durability, fire resistance, and fatigue performance of these members under combined loading conditions.