Engineering Application and Research Progress of Concrete-Filled Steel Tube Bridge Towers

Literature Overview

This comprehensive review by Liu, Sun, Zhou, Xian, Zhang, and Li (2022), published in the China Journal of Highway and Transport (Vol. 35, No. 6, pp. 1-21), provides an in-depth examination of the engineering application and research progress of concrete-filled steel tube (CFST) bridge towers for cable-supported bridges. Funded by the National Natural Science Foundation of China (Grant 51778058) and the Central University Basic Scientific Research Fund (Project 300102211709), the paper reviews existing CFST bridge tower configurations, identifies design challenges, proposes structural optimizations, and evaluates the mechanical performance and economic viability of CFST towers compared to conventional reinforced concrete and steel towers.

Current Engineering Application Status

CFST bridge towers have been applied in cable-stayed bridges, suspension bridges, and hybrid cable-supported bridges in China. The review identifies several common structural configurations:

• Single-cell circular CFST towers: Simplest form with a single circular steel tube filled with concrete.
• Multi-cell CFST towers: Multiple steel tubes arranged in H, A, or diamond configurations.
• Composite CFST towers: CFST members combined with steel or reinforced concrete elements.

The paper notes that current CFST tower designs tend to be overly complex due to insufficient understanding of the steel-concrete composite action, particularly regarding the local buckling behavior of steel plates under one-sided concrete confinement and the load transfer mechanism at the steel-concrete interface.

Key Design Challenges and Structural Optimization

The authors identify three primary design challenges:

1. Insufficient understanding of steel-concrete composite load-carrying mechanisms: The interaction between the steel tube and concrete infill under combined axial, bending, and shear loading is not fully characterized.
2. Weak theoretical foundation for local buckling of one-sided confined steel plates: The local buckling behavior of steel plates confined by concrete on only one side differs significantly from that of fully confined steel plates, yet theoretical models are limited.
3. Unclear steel-concrete interface load transfer performance: The bond strength, slip behavior, and load transfer mechanism at the steel-concrete interface under cyclic loading remain inadequately understood.

To address these challenges, the authors propose an optimized CFST tower configuration known as the PBL (Plate Beam-Lattice) stiffened CFST tower, which features:

• Simplified stiffening configurations that enhance the constraining effect of the steel wall on the concrete
• Streamlined steel-concrete connection details that reduce fabrication complexity
• Elimination of internal reinforcement requirements, reducing steel consumption and simplifying the manufacturing process
• Improved industrialization potential for prefabricated tower segments

Mechanical Performance and Design Methods

The paper reviews the research progress on the mechanical performance of CFST tower members:

• Local buckling of steel wall plates: The local buckling behavior is governed by the slenderness ratio (D/t), material properties, concrete strength, and the degree of concrete confinement. The proposed design method accounts for local buckling effects in the stiffened steel wall plate configuration.
• Tower member load-carrying capacity: The recommended design method incorporates the interaction between axial force, bending moment, and shear force, with explicit consideration of local buckling degradation.
• Steel-concrete interface behavior: The interface bond strength and slip capacity are critical for the composite action of CFST tower members, particularly under cyclic loading conditions typical of wind and traffic-induced vibrations.

Economic Comparison and Technical Advantages

The economic analysis demonstrates that CFST towers offer construction and maintenance costs significantly lower than steel towers, while being competitive with reinforced concrete towers. The key advantages include design flexibility, construction efficiency, and high disaster resilience due to the composite action of steel and concrete.

Engineering Practice and Quality Control Implications

From a steel pipe manufacturing and welding engineering perspective, the CFST bridge tower application presents several critical considerations:

1. Steel tube manufacturing for tower segments: Tower segments typically require large-diameter steel tubes (1,000-3,000 mm diameter) with wall thicknesses of 20-50 mm. UOE forming or plate-welded fabrication methods are employed, with strict dimensional tolerances and material certification requirements.
2. Welding of tower segment joints: Field welding of tower segments is performed at elevated heights with complex access conditions. Multi-pass submerged arc welding (SAW) or flux-cored arc welding (FCAW) is typically employed, with rigorous welder qualification and welding procedure qualification requirements.
3. Steel-concrete interface quality: The quality of the steel-concrete interface is critical for composite action. Surface preparation of the steel tube interior, concrete mix design with appropriate workability, and proper concrete placement methods (including vibration) are essential for achieving adequate bond strength.
4. Non-destructive testing: Critical welds at tower segment joints, stiffener connections, and cable anchorages must undergo comprehensive NDT including UT, MT, and PT. The acceptance criteria should be stringent given the safety-critical nature of bridge towers.
5. Corrosion protection: The steel components of CFST towers are exposed to atmospheric and potentially marine environments. Coating systems, galvanization, and cathodic protection must be specified to ensure adequate service life.

The research presented in this paper demonstrates that CFST bridge towers represent a promising structural solution for cable-supported bridges, offering a favorable combination of structural performance, construction efficiency, and economic viability. The proposed PBL stiffened CFST tower configuration addresses the key design challenges identified in current practice and provides a practical pathway toward wider adoption. Engineers involved in the design and fabrication of CFST bridge towers should closely follow the research progress in this field, particularly regarding local buckling theory, steel-concrete interface behavior, and advanced design methods that account for composite action under complex loading conditions. The continued refinement of manufacturing techniques, welding procedures, and quality control protocols will be essential for realizing the full potential of CFST bridge towers in future bridge engineering projects.