Seismic Performance Comparison of Steel Bone-Steel Tube Concrete Frame Structures

Literature Overview

This paper by Tan Yanqiu, Han Xufei, Shi Sanyuan, and Zhang Honglei, published in the Journal of Hebei Engineering University (Natural Science Edition) (2011, Vol. 28, No. 3), compares the seismic performance of steel bone-steel tube concrete (SRC) frame structures with conventional steel tube concrete (SRCF) frame structures. The study was supported by the Hebei Provincial Natural Science Foundation (E2010001012). Using SAP2000 finite element analysis software, the authors performed modal analysis and elasto-plastic time-history analysis of both structural systems, and compared the results with an 8-story steel tube concrete frame structure and a steel bone-steel tube concrete frame structure project.

Structural System Description and Steel Pipe Integration

The steel bone-steel tube concrete frame system combines the advantages of both steel tube concrete columns and steel-reinforced concrete columns. The steel bone (typically an H-section or box-section steel profile) is embedded within the steel tube concrete column, providing enhanced flexural strength and ductility. This hybrid system represents an advanced structural approach that leverages the composite action of steel and concrete while maintaining the efficient use of steel material.

From a steel pipe manufacturing and fabrication standpoint, the integration of a steel bone within a steel tube concrete column introduces several technical considerations:

• The steel bone must be precisely positioned within the steel tube to ensure proper concrete placement and composite action.
• The connection between the steel bone and the steel tube (if any) must be designed to accommodate differential thermal expansion and concrete shrinkage.
• The welding of the steel bone to the steel tube at critical locations (typically at the column ends and beam-column joints) requires careful procedure qualification to ensure adequate joint strength.

Seismic Performance Analysis Results

The comparative analysis reveals that the steel bone-steel tube concrete frame structure outperforms the conventional steel tube concrete frame structure in several key seismic performance indicators:

The superior seismic performance of the steel bone-steel tube concrete frame is attributed to the additional flexural capacity and ductility provided by the embedded steel bone. The steel bone acts as an internal reinforcement that enhances the bending moment resistance of the column, particularly at the plastic hinge regions that develop during seismic loading.

Welding and Connection Design for Seismic Applications

The seismic design of steel bone-steel tube concrete frames requires special attention to the welding connections between the steel bone and the steel tube. These connections must be designed to accommodate:

1. Large inelastic deformations during seismic events without fracture or excessive local buckling.
2. Repeated cyclic loading without fatigue failure.
3. Potential concrete spalling and loss of confinement around the connection zone.

The welding procedure for these connections should follow the requirements of seismic design codes such as GB 50011-2010 (Code for Seismic Design of Buildings) and the relevant welding codes (GB 50661-2011 for steel structures). Key requirements include:

• Full-penetration welds at critical connections to ensure ductile failure mode.
• Controlled heat input to minimize the size of the heat-affected zone and prevent excessive grain growth.
• Post-weld inspection using advanced NDT methods (PAUT or TOFD) to detect volumetric defects that could initiate under cyclic loading.
• Consideration of welding residual stresses in the seismic design analysis, as these stresses can reduce the effective yield strength of the steel tube walls.

Modal Analysis and Structural Behavior

The modal analysis results provide insight into the natural frequencies and mode shapes of both structural systems. The steel bone-steel tube concrete frame typically exhibits higher natural frequencies due to the increased stiffness from the embedded steel bone. However, the elasto-plastic time-history analysis reveals that the additional stiffness is accompanied by superior energy dissipation capacity, resulting in lower peak responses under seismic loading.

The hysteresis behavior comparison is particularly significant from a structural engineering perspective. The steel bone-steel tube concrete frame exhibits fuller and more stable hysteresis loops, indicating superior energy dissipation capacity and ductility. This behavior is attributed to the yielding of the steel bone in the plastic hinge regions, which provides a ductile failure mode that absorbs significant seismic energy without catastrophic collapse.

Engineering Practice and Design Recommendations

The study provides valuable guidance for the design of seismic-resistant steel tube concrete frame structures. The incorporation of steel bones into steel tube concrete columns offers a practical approach to enhancing seismic performance without significantly increasing the structural weight or construction complexity. For steel pipe suppliers and fabricators, the key requirements include:

• Precise dimensional control of the steel tubes to ensure proper fit-up with the embedded steel bones.
• High-quality welding of the steel bone-to-steel tube connections with full compliance with seismic welding requirements.
• Material certification and mechanical property verification for both the steel tube material and the steel bone material.
• Consideration of the interaction between welding residual stresses and seismic loading in the structural design analysis.

The elasto-plastic time-history analysis methodology used in this study should be adopted as a standard verification tool for all seismic design of steel tube concrete frame structures, particularly those incorporating steel bones or other internal reinforcement elements.