Zhuojin Pipe Fitting Co., LtdSeismic Performance of Multi-Chamber Steel Tube Concrete Columns with Different Cross-Sectional Configurations
Literature Overview
This research by Cao Wanlin, Chen Xiangjia, Wu Haipeng, and Qiao Qiyun from the School of Civil Engineering at Beijing University of Technology, published in Structural Engineers journal in 2016, investigates the seismic performance of multi-chamber steel tube concrete (MCSTC) columns with unconventional cross-sectional shapes. The study was supported by the National Natural Science Foundation Major Research Program Integration Project (91315301) and the National Natural Science Foundation Project (51178010). The research is directly motivated by the design of the Dalian International Trade Center, which employs pentagonal multi-chamber STC mega-columns.
Core Technical Content
The authors conducted low-cycle reversed loading tests on four 1/7.5-scale model specimens representing two different cross-sectional configurations of pentagonal multi-chamber STC columns:
- Group 1: Chamber-separating vertical steel plates continuous at the base level
- Group 2: Chamber-separating vertical steel plates discontinuous (broken) at the base level
Each group was tested under two loading directions: along the cross-sectional symmetry axis and perpendicular to the symmetry axis. The tests examined failure characteristics, load-bearing capacity, energy dissipation, stiffness degradation, hysteresis characteristics, and ductility.
Cross-Sectional Configuration Analysis
The pentagonal multi-chamber STC column represents an advanced structural system where a single large column is divided into multiple chambers by internal steel plates. This configuration offers several structural advantages:
| Configuration Feature | Continuous Steel Plates | Discontinuous Steel Plates |
|---|---|---|
| Load-bearing capacity | Higher | Slightly lower |
| Ductility | Better | Moderate |
| Energy dissipation | Stronger | Moderate |
| Directional symmetry of seismic response | Significant difference between two directions | Nearly symmetric between two directions |
| Base-level detailing complexity | Higher (continuous plates require careful detailing) | Lower (plates can terminate at base) |
| Construction at foundation interface | More complex | Simpler |
The key finding is a trade-off between seismic performance and construction practicality. Continuous vertical steel plates provide superior seismic performance due to their ability to maintain composite action throughout the column height, including at the critical base region. However, the discontinuous configuration offers nearly symmetric seismic response regardless of loading direction, which is advantageous for irregular loading scenarios.
Failure Mechanism and Ductility Assessment
The failure patterns observed in the tests provide valuable insight into the structural behavior of multi-chamber STC columns:
- Continuous plate configuration: Failure typically initiates at the base where the continuous steel plates create a rigid constraint. The concrete in the chambers adjacent to the continuous plates experiences higher compressive stresses, leading to earlier concrete crushing. However, the overall ductility is enhanced because the continuous plates provide confinement that prevents premature lateral buckling of the steel tube walls.
- Discontinuous plate configuration: Failure is more uniformly distributed across chambers because the plates do not create rigid constraints at the base. The concrete crushing occurs more gradually, but the overall ductility is somewhat reduced due to less effective composite action at the base.
The directional asymmetry in the continuous plate configuration is particularly important for seismic design. When loading is applied along the symmetry axis, the column behaves differently than when loaded perpendicular to it. This asymmetry must be accounted for in seismic design through appropriate capacity design procedures.
Engineering Practice Considerations
For steel pipe manufacturers and structural engineers involved in multi-chamber STC column design, several practical aspects emerge:
- Steel tube wall thickness: The outer steel tube and internal chamber-separating plates must be designed with sufficient thickness to resist buckling under combined axial and flexural loading. The internal plates, being thinner than the outer tube, are particularly susceptible to local buckling.
- Welding of chamber-separating plates: The longitudinal welds connecting the internal steel plates to the outer tube wall must be designed for fatigue and cyclic loading. The weld quality directly affects the composite action between chambers.
- Base detailing: The choice between continuous and discontinuous plate configurations at the base has significant implications for fabrication and erection. Continuous plates require precise alignment and welding at the foundation interface, which can be challenging in large-diameter mega-columns.
- Concrete placement: Multi-chamber columns require careful concrete placement to ensure full filling of each chamber without voids. The presence of internal plates creates additional challenges for concrete flow and compaction.
Numerical Scale and Testing Methodology
The use of 1/7.5-scale models represents a practical compromise between full-scale testing feasibility and geometric similarity. The scale factor affects several aspects of the test results:
| Scale Effect | Implication |
|---|---|
| Size effect on concrete crushing | Smaller specimens may show higher apparent strength |
| Weld scale | Welds are proportionally smaller, potentially affecting weld quality |
| Loading rate effects | Must maintain strain-rate equivalence |
| Boundary condition representation | Simplified boundary conditions may not fully represent actual behavior |
The experimental program design, with two configurations and two loading directions per configuration, provides a comprehensive dataset for evaluating the seismic performance of multi-chamber STC columns. The low-cycle reversed loading protocol simulates the cyclic nature of seismic loading and allows assessment of ductility and energy dissipation capacity.
Key Reflections
This research addresses a critical gap in the understanding of unconventional cross-sectional STC columns. The pentagonal multi-chamber configuration is a departure from conventional circular or square STC columns, and the seismic behavior is fundamentally different due to the complex interaction between chambers. The finding that continuous plate configuration provides superior seismic performance but with directional asymmetry, while discontinuous configuration provides more symmetric response but with slightly reduced capacity, offers designers a clear trade-off to consider.
From a steel pipe fabrication standpoint, the internal chamber-separating plates represent additional steel components that must be manufactured, transported, and erected within the column assembly. The welding requirements for these plates, particularly at the base where continuous or discontinuous configurations diverge, demand careful procedural planning and quality control.
Summary
The experimental investigation of multi-chamber STC columns with different base-level steel plate configurations reveals important trade-offs between seismic performance and construction practicality. Continuous vertical steel plates at the base provide higher load-bearing capacity, better ductility, and stronger energy dissipation, but introduce significant directional asymmetry in seismic response. Discontinuous plates offer nearly symmetric seismic performance with slightly reduced capacity. Engineers designing multi-chamber STC columns must carefully evaluate the seismic loading scenarios and construction constraints to select the optimal configuration, while ensuring that welding quality and concrete placement practices support the predicted structural performance.