Zhuojin Pipe Fitting Co., LtdSeismic Performance of Prefabricated Square Steel Tube Constrained Concrete Bridge Piers with Hybrid Joints
Literature Overview
This paper by Ou Zhijing, Cao Lei, and Xue Wenhao from Fujian Engineering University investigates the seismic behavior of prefabricated square-section concrete bridge piers that incorporate a hybrid joint system combining grouted sleeves with steel tube shear keys, and are further confined by square steel tubes. Published in Bridge Construction (Vol. 53, No. 1, 2023), the research addresses a critical gap in the seismic design of modular bridge pier systems. Three specimens were fabricated and tested under quasi-static loading: one with hybrid joint plus square steel tube confinement, one with grouted sleeve joint only plus confinement, and one with grouted sleeve joint without confinement. The study was supported by the National Natural Science Foundation of China (51878172) and Fujian Provincial funding programs.
Core Technical Findings
All three specimens exhibited a similar failure mode of compression-bending failure, which is consistent with the expected behavior of slender bridge piers under cyclic lateral loading. However, significant differences emerged in terms of seismic performance indicators. The square steel tube confined specimens demonstrated higher peak horizontal load capacity and displacement ductility coefficients compared to the unconstrained specimen. More notably, the hybrid joint specimen produced fuller hysteresis loops with no obvious pinching, indicating superior energy dissipation capacity and more stable cyclic response compared to the grouted sleeve-only joint configuration.
Key Performance Indicators
| Performance Parameter | Hybrid Joint + Confinement | Grouted Sleeve + Confinement | Grouted Sleeve Only |
|---|---|---|---|
| Failure Mode | Compression-bending | Compression-bending | Compression-bending |
| Peak Horizontal Load | Highest | Moderate | Lowest |
| Displacement Ductility | Highest | Moderate | Lowest |
| Hysteresis Loop Fullness | Full, no pinching | Some pinching | Significant pinching |
| Residual Displacement | Lower | Moderate | Higher |
| Stiffness Degradation Rate | Slower | Moderate | Faster |
Influence of Design Parameters
For the hybrid joint prefabricated square steel tube confined concrete bridge pier, the authors identified several critical design parameters through parametric finite element analysis. Increasing the axial compression ratio and decreasing the slenderness ratio improve bearing capacity but reduce ductility. Conversely, increasing the confinement coefficient enhances both bearing capacity and ductility. Based on these findings, the authors recommend an axial compression ratio of 0.3 or less, a slenderness ratio of 12 or less, and a confinement coefficient in the range of 0.58 to 0.90 for optimal seismic performance.
Technical Interpretation and Engineering Implications
From a steel pipe fabrication and welding perspective, this study highlights several important aspects. The square steel tube confinement acts as a passive restraint system that prevents concrete spalling and maintains core integrity during seismic events. The steel tube shear keys within the hybrid joint serve as additional load transfer mechanisms that supplement the grouted sleeve connection, providing redundancy in the joint design. This dual-mechanism approach is particularly valuable for prefabricated systems where field connection quality is difficult to guarantee.
The hybrid joint concept deserves careful consideration in engineering practice. Grouted sleeves alone rely heavily on the bond strength between the steel bar and grout, which can be sensitive to grout quality, curing conditions, and surface preparation. The addition of steel tube shear keys introduces a mechanical interlock that is less dependent on material interface quality. In terms of welding, the steel tube shear keys require precise fabrication with controlled weld quality, as any weld defects could compromise the load transfer capacity of the joint. The square steel tube confinement itself must be fabricated with attention to dimensional accuracy, particularly at the corners where bending stresses concentrate during seismic deformation.
Welding and Fabrication Considerations
- Square steel tubes require careful corner weld inspection to ensure full penetration and absence of porosity or lack of fusion defects.
- Steel tube shear keys demand high-precision cutting and welding to maintain proper engagement with the grouted sleeve assembly.
- The confinement coefficient depends on the steel tube dimensions and material grade, requiring precise dimensional control during fabrication.
- Residual stresses from welding the square steel tube frame can affect the initial stiffness of the confined concrete section and should be managed through appropriate welding sequences and post-weld stress relief.
Study Insights and Reflections
This research contributes meaningfully to the seismic design methodology for modular bridge piers. The recommendation of confinement coefficient between 0.58 and 0.90 provides a practical design window that balances material efficiency with structural performance. The finding that the hybrid joint eliminates hysteresis pinching is particularly significant, as pinching behavior in joints is a major contributor to cumulative damage in seismic events. For steel pipe manufacturers and fabricators, this study underscores the growing demand for high-quality square steel tubes with controlled tolerances and certified weld quality for seismic-resistant prefabricated bridge components. The integration of steel tube confinement with advanced joint systems represents a promising direction for resilient infrastructure construction, and the parametric recommendations provide a solid foundation for further design code development.