Zhuojin Pipe Fitting Co., LtdConstruction Force Performance and Stability of CFST Tied-Arch Bridges
Project Background and Technical Context
This study by Chen Fan and colleagues, conducted in the context of the South-to-North Water Diversion Project's Yaowan Canal Crossing Road Bridge in Nanyang, Henan Province, addresses a critical practical challenge in steel tube-confined concrete (CFST) tied-arch bridge construction. Tied-arch bridges are increasingly favored for their aesthetic appeal and efficient use of materials, but the construction sequence introduces complex temporary load states that differ significantly from the final design conditions. The paper employs three-dimensional finite element analysis to simulate the entire construction process, providing theoretical guidance for construction monitoring.
Construction Sequence Analysis
Construction Stages and Load Evolution
The construction of a CFST tied-arch bridge involves multiple sequential operations, each introducing distinct load patterns:
| Construction Stage | Primary Load Source | Critical Monitoring Parameter |
|---|---|---|
| Steel arch rib erection | Self-weight of steel tubes | Temporary support reactions |
| Concrete pouring (branch-by-branch) | Wet concrete weight, differential filling | Branch tube stress distribution |
| Concrete creep period | Stress redistribution due to creep | Long-term stress state |
| Hanger cable tensioning | Cable tension forces | Arch rib axial force and moment |
| Tie beam multi-stage tensioning | Tie beam prestress | Arch-thrust equilibrium |
| Deck casting and loading | Superstructure self-weight | Final stress state verification |
Concrete Pouring Sequence Effects
One of the most significant findings is that the compressive stress in the concrete within each branch tube is strongly dependent on the pouring sequence. When branches are poured sequentially rather than simultaneously, the first-poured branches experience higher initial stresses due to the asymmetrical loading of the arch rib. This creates a non-uniform stress distribution across the arch cross-section that may persist into the service condition. From a steel pipe quality perspective, this means that the steel tubes in the first-poured branches experience higher hoop stresses, potentially leading to earlier onset of local buckling if the wall thickness is insufficient.
Creep-Induced Stress Redistribution
The paper highlights that concrete creep within the steel tubes causes significant stress redistribution over time. As the concrete creeps under sustained load, it transfers stress from the concrete core to the steel tube, progressively increasing the hoop tension in the steel tube wall. This long-term stress redistribution is a critical consideration for the durability and long-term stability of CFST arch ribs. For steel pipe suppliers, this implies that the steel tube's long-term strength retention and resistance to creep-induced fatigue must be verified, particularly for tubes with thinner wall-to-diameter ratios.
Stability Analysis of Construction Supports
The temporary support system (shoring) for the arch ribs during construction must satisfy both global stability and branch stability requirements. The analysis confirms that the support system meets these criteria, but the study emphasizes that:
- Global stability: The overall support structure must resist the combined effects of arch rib self-weight, concrete pouring loads, and potential wind loads during construction.
- Branch stability: Individual support legs must resist local buckling under concentrated loads from the arch rib contact points.
- Dynamic effects: The pouring of concrete introduces dynamic impact loads that may not be captured in static analysis but can trigger local instability in slender support members.
Engineering Practice Recommendations
For steel pipe manufacturers supplying tubes for CFST arch bridges, the following quality control measures are recommended:
- Wall thickness uniformity: Tight tolerance control (within ±10% of nominal) is essential, as non-uniform wall thickness creates weak sections susceptible to local buckling under the high hoop stresses developed during and after construction.
- Material certification: Each steel tube batch must be accompanied by full mechanical property documentation, including yield strength, ultimate tensile strength, elongation, and impact toughness at the service temperature.
- Weld quality verification: For multi-branch arch ribs assembled from welded tubes or tube segments, ultrasonic testing (UT) and radiographic testing (RT) of all welds are mandatory, with acceptance criteria aligned to GB/T 3323 or ASME Section V.
- Surface preparation: The internal surface of the steel tubes must be clean, free from rust, scale, and contaminants, to ensure proper bond between the steel tube and the poured concrete. Shot blasting to Sa 2.5 grade is recommended.
Study Insights
This research reinforces the principle that construction-stage analysis is not merely a procedural requirement but a fundamental engineering necessity for CFST structures. The stress states developed during construction—particularly during the transient phases of concrete pouring and creep—may govern the design more critically than the final service loads. Steel pipe engineers and quality control inspectors should be aware that the manufacturing tolerances and material properties of the steel tubes directly influence the construction-stage behavior, and any deviation from specification can compromise the structural integrity during the most vulnerable construction phases.