Zhuojin Pipe Fitting Co., LtdSeismic Performance of Steel Tube Concrete Composite Column Frame with Embedded Steel Truss Core Wall
Literature Overview
This study by Dong Hongying, Yang Xinqiang, Cao Wanlin, Zhang Jianwei, and Geng Haixia from Beijing University of Technology was published in Earthquake Engineering and Engineering Dynamics (2011, Vol. 31, No. 1, pp. 41–47). Funded by the National Natural Science Foundation of China (50878007), Beijing Science and Technology Major Project (D08050603720000), Beijing High-Level Talent Project (PHR20100502), and Beijing Municipal Education Commission Key Science and Technology Plan Project (KZ200910005008), the research investigates the seismic performance of a hybrid core wall system that combines steel tube-concrete composite columns with an embedded steel truss.
Core Technical Content
The study proposed a novel composite core wall system consisting of a steel tube-concrete composite column frame surrounding a reinforced concrete core, with a steel truss embedded within the core wall. Two 1/6-scale specimens were tested under low-cycle reversed loading to evaluate and compare their seismic performance:
- Specimen A: Steel tube-concrete composite column frame combined core wall (without embedded steel truss)
- Specimen B: Steel tube-concrete composite column frame with embedded steel truss combined core wall
The comparison focused on bearing capacity, ductility, stiffness and its degradation, hysteresis characteristics, energy dissipation capacity, and failure characteristics.
Performance Comparison
| Performance Indicator | Specimen A (Without Truss) | Specimen B (With Truss) | Improvement |
|---|---|---|---|
| Bearing capacity | Baseline | Increased | Significant |
| Ductility | Baseline | Improved | Moderate to significant |
| Stiffness degradation rate | Faster | Slower | Improved |
| Hysteresis loop fullness | Baseline | Fuller loops | Better energy dissipation |
| Energy dissipation capacity | Baseline | Enhanced | Significant |
| Failure mode | Concrete crushing and column yielding | Controlled failure with truss yielding | More ductile |
The study developed a bearing capacity calculation model for the composite core wall with embedded steel truss, and the calculated results showed good agreement with experimental measurements.
Structural Mechanism Analysis
The embedded steel truss plays a critical role in enhancing the seismic performance of the core wall through several mechanisms:
- Shear reinforcement: The truss members provide direct shear resistance, supplementing the shear capacity of the concrete core wall and reducing the reliance on diagonal tension cracks.
- Load redistribution: The truss distributes lateral forces more uniformly across the core wall section, reducing localized stress concentrations.
- Ductility enhancement: The yielding of truss members provides a ductile failure mode that precedes concrete crushing, allowing the structure to undergo larger displacements before collapse.
- Stiffness stabilization: The truss provides additional lateral stiffness that slows the rate of stiffness degradation under cyclic loading.
The steel tube-concrete composite columns serve as the boundary elements of the core wall, providing confinement to the concrete and contributing to the overall lateral load resistance. The composite action between the steel tube and concrete is achieved through the Poisson effect and mechanical interlock at the steel-concrete interface.
Engineering Practice Integration
From a steel pipe and welding perspective, the implementation of this composite core wall system has several important considerations:
- Steel tube fabrication: The steel tubes used for the composite columns must be manufactured with high dimensional accuracy and surface quality to ensure proper fit-up with the formwork and reinforcement cage. Common specifications include Q345B or Q390B steel tubes with wall thicknesses of 8–20 mm, depending on the structural demand.
- Welding connections: The connections between the steel tubes and the embedded steel truss are critical load paths. These connections typically involve butt welds or fillet welds that must be designed and inspected in accordance with seismic welding standards (e.g., GB 50661 or AWS D1.1). The weld details should be designed to ensure that yielding occurs in the truss members rather than in the welds.
- Truss fabrication: The steel truss members are typically fabricated from structural steel H-beams or round bars. The welding of truss nodes requires careful attention to weld quality, as these are high-stress regions that must maintain integrity under cyclic loading.
Study Insights and Reflections
The concept of embedding a steel truss within a concrete core wall represents a hybrid structural approach that combines the compressive strength of concrete with the tensile and shear capacity of steel. This approach is particularly effective in regions where concrete core walls are commonly used but seismic performance demands exceed what conventional reinforced concrete can provide.
The 1/6-scale model testing approach is a standard practice in structural engineering research, allowing the study of full-scale structural behavior at a manageable scale. However, scale effects must be considered when extrapolating results from model to full scale, particularly regarding the size effect on concrete fracture and the strain rate sensitivity of steel under cyclic loading.
The bearing capacity calculation model developed in this study provides a practical tool for designers. The model likely incorporates the contributions of the concrete core wall, the steel tube-concrete composite columns, and the embedded steel truss, with appropriate interaction terms to account for the composite action between these components.
One area for further investigation is the long-term durability of the embedded steel truss. If the truss is embedded within the concrete core wall, the protection of the steel members from corrosion depends on the concrete cover quality and the alkalinity of the concrete pore solution. In aggressive environments, additional corrosion protection measures such as epoxy coating or the use of stainless steel truss members may be necessary.
Reference Value and Outlook
This research provides experimental evidence and analytical tools for the seismic design of hybrid core wall systems with embedded steel trusses. The findings support the adoption of this structural system in high-seismicity regions where enhanced lateral load resistance and ductility are required. For the steel pipe industry, the study highlights the demand for high-quality steel tubes with consistent mechanical properties for use in composite structural columns. Future research should extend to full-scale testing, investigate the interaction with floor diaphragms and beam-column connections, and develop code provisions for the design of these hybrid systems.