Zhuojin Pipe Fitting Co., LtdDesign and Construction of Concrete-Filled Steel Tubular Columns in Wuhan Jianghan Third Bridge
Literature Overview
This paper by Ding Qingjun, Guan Binjun, and Hu Shuguang from Wuhan University of Technology and Hubei University documents the design and construction of concrete-filled steel tubular (CFST) columns in the Jianghan Third Bridge in Wuhan, China. Published in the journal Concrete in 2000, the study was supported by the Ministry of Transport's Ninth Five-Year Key Project. The paper provides a practical case study of CFST column construction in a major bridge project, focusing on concrete mix design, pumping technology, and quality verification methods.
Concrete Mix Design and Construction Technology
The CFST columns in the Jianghan Third Bridge required high-strength, early-strength, and slightly expansive concrete to ensure reliable structural performance and construction efficiency. The concrete mix design incorporated the following key considerations:
| Mix Design Parameter | Specification | Purpose |
|---|---|---|
| Compressive strength | High-strength grade | Meet structural load requirements |
| Early strength development | Rapid strength gain | Accelerate construction schedule |
| Expansion characteristics | Micro-expansion | Compensate for shrinkage and ensure full concrete-steel bond |
| Pumpability | Workable mix | Enable vertical pumping through steel tubes |
The construction process involved pumping concrete through the top opening of the steel tube. Given the vertical height of the bridge columns, the concrete mix was specifically designed to maintain its workability during pumping without excessive segregation. The micro-expansion characteristic of the concrete was particularly important for ensuring complete filling of the steel tube without voids, especially in regions with complex geometry such as the interface between the main tube and the缀板 (tie plates).
Quality Verification Methods
The paper describes a comprehensive quality verification program employing multiple non-destructive and destructive testing methods:
- Hammer testing: Visual and tactile inspection of the filled steel tubes to detect surface irregularities or incomplete filling.
- Ultrasonic testing (UT): Non-destructive evaluation to detect internal voids, cracks, or incomplete concrete placement within the steel tubes.
- Core drilling: Destructive sampling to verify concrete strength, density, and homogeneity at various locations within the filled tubes.
The inspection results confirmed that the concrete within the steel tubes and between the tie plates was dense and free of cracks. This comprehensive verification approach is consistent with the quality control principles outlined in GB 50936-2014 and provides a model for quality assurance in CFST construction projects.
Engineering Practice Implications
From a welding and fabrication standpoint, the steel tubes used in bridge CFST columns are typically manufactured from carbon structural steel such as Q235 or Q345. The fabrication process involves rolling, cutting, forming, and welding of the steel tubes. For large-diameter tubes used in bridge columns, longitudinal submerged-arc welding (LSAW) is commonly employed, while smaller diameter tubes may be produced by electric resistance welding (ERW) or high-frequency welding (HFW). The welding quality of the steel tubes is critical for the overall structural integrity, as weld defects can propagate under service loads and compromise the composite action between the steel tube and the concrete infill.
The pumping process requires careful management of the concrete delivery system. The use of tremie pipes or internal vibrators ensures proper consolidation of the concrete within the confined space of the steel tube. The pumping rate must be controlled to prevent excessive pressure buildup that could cause local buckling of the steel tube, particularly in regions with reduced wall thickness or at welded joints. From a metallurgical perspective, the residual stresses induced by the pumping process and the thermal effects of concrete hydration can influence the long-term behavior of the steel tube. Therefore, the selection of steel grade with adequate toughness and the control of welding residual stresses through post-weld heat treatment or mechanical stress relief are important considerations.
Study Insights and Implications
This case study provides practical guidance for the design and construction of CFST columns in bridge engineering. The emphasis on concrete mix design optimization, particularly the incorporation of micro-expansion characteristics, demonstrates the importance of material engineering in achieving reliable structural performance. The multi-method quality verification approach highlights the need for comprehensive non-destructive testing in CFST construction, consistent with the quality control requirements of standards such as GB 50936 and JTG/T 3512-2019.
In my experience with steel pipe manufacturing, I have observed that the surface quality of the steel tube interior significantly affects the bond between the steel and the concrete. Tubes with excessive mill scale or rust contamination may exhibit reduced bond strength, leading to slippage under cyclic loading. Therefore, the surface preparation of steel tubes before concrete placement, including shot blasting or chemical cleaning to achieve a clean, roughened surface, is an essential quality control step. The findings of this study reinforce the importance of integrating material science, fabrication technology, and quality assurance in the successful implementation of CFST construction.