Zhuojin Pipe Fitting Co., LtdSeismic Performance Analysis of Rectangular Concrete-Filled Steel Tube High-Strength Concrete Frames
Literature Overview
The paper by Guan Minsheng, Huang Xianqi, Du Hongbiao, and Zhang Jingang, published in the Journal of Southwest Jiaotong University (2019, Vol. 54, No. 3), investigates the seismic performance of rectangular concrete-filled steel tube (CFST) high-strength concrete frames through low-cycle reversed loading tests and finite element analysis. Funded by Shenzhen Science and Technology Research Fund and Shenzhen University, this research examines the failure mechanism, hysteresis behavior, and parametric effects on seismic performance. This study is highly relevant to engineers designing high-rise buildings in seismic zones using composite structural systems.
Core Technical Framework
The authors conducted low-cycle reversed loading tests on a single-bay two-story rectangular CFST high-strength concrete frame specimen and performed finite element analysis using Perform-3D software. The parametric study examined the effects of axial load ratio, steel yield strength, and lateral load application patterns on seismic performance.
| Performance Indicator | Test Result | Code Limit | Exceedance |
|---|---|---|---|
| Average peak load ratio | 1.68 times yield load | - | - |
| Top story drift ratio | 1/30 | 1/50 | 66.7% |
| Bottom story drift ratio | 1/27 | 1/50 | 85.2% |
| Ductility coefficient (top) | Exceeds limit | 3.0 | 58.5% |
| Ductility coefficient (bottom) | Exceeds limit | 3.0 | 60.0% |
Technical Points and Interpretation
The test results reveal that rectangular CFST high-strength concrete frames exhibit a beam-hinge failure pattern, which is the desired failure mode for seismic design. The frames demonstrate high load-bearing capacity, good deformation capacity, and excellent energy dissipation characteristics. The average peak load is 1.68 times the yield load, indicating significant post-yield reserve capacity.
The story drift ratios of 1/30 for the top story and 1/27 for the bottom story exceed the code-prescribed limits by 66.7% and 85.2%, respectively. These exceedances indicate that the frames have substantial deformation capacity beyond the code requirements, which provides a significant safety margin against collapse during severe earthquakes. The ductility coefficients also exceed the code limits by 58.5% and 60.0%, further confirming the excellent ductile behavior of the system.
The parametric analysis reveals several important findings. The axial load ratio has a significant influence on seismic performance, with a notable reduction in capacity and deformation capacity when the axial load ratio exceeds 0.6. This threshold is consistent with established design codes that limit the axial load ratio to prevent premature column failure. The lateral load application pattern also significantly affects capacity, with uniform loading providing the highest capacity, inverted triangular loading providing intermediate capacity, and vertex loading providing the lowest capacity.
Welding and Steel Pipe Fabrication Considerations
The fabrication of rectangular CFST frame members involves longitudinal and transverse welding of steel plates to form the rectangular tubes, followed by concrete infilling. The quality of the longitudinal and transverse welds is critical because these welds form the primary structural connections within the frame members. Submerged arc welding (SAW) or flux-cored arc welding (FCAW) processes are commonly used for these welds, and rigorous NDT protocols including UT and RT are essential to detect internal defects.
The beam-column connections in rectangular CFST frames are typically designed as rigid connections to ensure the frame action mechanism. The welding of connection plates to the CFST members must be carefully detailed to accommodate the large inelastic deformations expected during seismic events. Welding-induced residual stresses in the connection regions can reduce the local buckling resistance of the steel tube and affect the connection's rotation capacity. Stress-relief welding or post-weld heat treatment may be required for high-strength steels to prevent delayed cracking.
The high-strength concrete used in these frames (typically 60-80 MPa or higher) presents challenges for concrete placement and consolidation within the rectangular steel tubes. The confined space and the presence of internal reinforcement require careful planning of concrete pumping and vibration procedures. The quality of the concrete-steel tube bond is important for composite action, and surface preparation of the steel tube interior, including cleaning and possible roughening, is recommended.
Engineering Practice Implications
The research provides valuable design guidance for rectangular CFST high-strength concrete frames in seismic zones. The beam-hinge failure pattern observed in the tests confirms that the system achieves the desired performance objective when properly designed. Engineers should ensure that the design axial load ratio does not exceed 0.6 to maintain adequate deformation capacity, and should select an appropriate lateral load application pattern for analysis that reflects the actual seismic demand on the structure.
The significant exceedance of code-prescribed drift and ductility limits indicates that the system has substantial reserve capacity. This finding supports the use of rectangular CFST high-strength concrete frames in critical structures where enhanced seismic performance is required. However, engineers should not rely solely on these exceedances for design, as the test conditions may not capture all the complexities of real-world seismic events.
The finite element analysis using Perform-3D provides a reliable tool for parametric studies and detailed design analysis. Engineers should use nonlinear finite element analysis for the design of critical connections and for evaluating the seismic performance of the complete structural system. The analysis should include appropriate material models for the steel tubes, high-strength concrete, and their composite interaction.
Key Reflections and Study Insights
This research demonstrates that rectangular CFST high-strength concrete frames are an effective structural system for seismic applications. The combination of the ductility of steel tubes and the compressive strength of high-strength concrete creates a composite system with excellent load-bearing and energy dissipation characteristics. The beam-hinge failure pattern observed in the tests is the ideal failure mode for seismic design, as it ensures that inelastic deformation is concentrated in the beams while the columns remain elastic.
The finding that the axial load ratio of 0.6 is a critical threshold is consistent with established design codes and provides a clear design guideline. Engineers should carefully control the axial load ratio in column design to ensure that the columns do not become the weak links in the structural system. The influence of lateral load application pattern on capacity highlights the importance of selecting an appropriate analysis model that accurately represents the seismic demand on the structure.
The research also underscores the importance of experimental validation of numerical models. The combination of physical testing and finite element analysis provides a comprehensive understanding of the structural behavior and validates the analytical tools used for design. Engineers should employ this combined approach for the design of critical structures to ensure reliable predictions of seismic performance.
Summary
This study demonstrates that rectangular CFST high-strength concrete frames exhibit excellent seismic performance with high capacity, large deformation capacity, and good energy dissipation characteristics. The research provides practical design guidance regarding axial load ratio limits and lateral load application patterns, and offers important insights for the fabrication, welding, and quality control of composite frame structures in seismic zones.