Zhuojin Pipe Fitting Co., LtdAnalysis of Mixed Construction Methods for Steel Tube Concrete Arch Bridges
Literature Overview
The paper by Tang Jishun, Hu Tao, Chen Yuanjiu, and Wu Xuwei from Southwest Jiaotong University, published in Sichuan Building Science (2017, Vol. 43, No. 6, pp. 122-126), addresses a practical construction challenge in steel tube concrete (CSTC) arch bridge erection. The study proposes a hybrid construction method that combines formwork-supported construction for the arch foot segments with cable-sling (hanging) construction for subsequent segments. This approach was developed for a specific through-arch CSTC bridge with complex site constraints, and the feasibility was verified through Midas/Civil finite element analysis.
Construction Methodology Comparison
The study compares two construction approaches:
| Construction Method | Applicable Segments | Equipment Required | Key Advantage | Key Limitation |
|---|---|---|---|---|
| Formwork-supported (scaffolding) | Arch foot segments | Scaffolding, formwork, concrete pump | High accuracy, stable working platform | Requires extensive ground support, site-dependent |
| Cable-sling (hanging) | Main arch segments | Cable-sling system, lifting equipment | Suitable for large spans, less ground interference | Line shape control is more challenging |
| Mixed method (proposed) | Combined approach | Both systems | Best of both methods | Complex transition between methods |
Technical Analysis of the Mixed Method
Design Rationale
The mixed construction method was proposed based on the following considerations:
- Arch foot segments: These segments experience the highest bending moments and require precise positioning and high-quality concrete placement. Formwork-supported construction provides the necessary stability and accuracy for these critical segments.
- Main arch segments: These segments benefit from the cable-sling method's ability to handle large spans with minimal ground support, reducing construction time and site disruption.
- Transition zone: The interface between the two construction methods requires careful engineering to ensure continuity of the arch structure and compatibility of internal forces.
Finite Element Analysis Results
The Midas/Civil analysis revealed the following key findings:
- Internal force distribution: The final internal force distribution in the completed arch is approximately the same regardless of whether the pure cable-sling method or the mixed method is used. This indicates that the construction method has limited influence on the final structural capacity.
- Line shape accuracy: The mixed construction method produces a final arch line shape that more closely matches the design line shape compared to the pure cable-sling method. This is because the formwork-supported arch foot segments provide a more accurate foundation for the subsequent cable-sling segments.
- Construction feasibility: The mixed method is technically feasible for bridges with suitable site conditions and high line shape accuracy requirements.
Key Technical Parameters
| Parameter | Design Consideration | Typical Value |
|---|---|---|
| Arch foot segment length | Depends on scaffolding span capability | 10-20 m |
| Cable-sling segment length | Determined by lifting capacity and stability | 8-15 m |
| Cable-sling angle | Affects vertical and horizontal force distribution | 30-60 degrees |
| Line shape tolerance | Depends on design requirements | ±10-20 mm |
| Concrete strength at cable-sling removal | Must develop sufficient strength | ≥70% of design strength |
Engineering Practice Considerations
Quality Control Points
For the successful implementation of the mixed construction method, the following quality control measures are essential:
- Scaffolding stability: The scaffolding system for arch foot segments must be designed for the combined weight of formwork, wet concrete, and construction loads, with adequate factor of safety.
- Transition zone treatment: The joint between formwork-supported and cable-sling segments must be designed for structural continuity, with proper reinforcement detailing and concrete compatibility.
- Line shape monitoring: Real-time monitoring of the arch line shape during construction is essential, with corrections applied through cable-sling tension adjustments.
- Concrete placement sequencing: The timing of concrete placement in each segment must be coordinated with the cable-sling system to avoid excessive deformation before concrete hardening.
Risk Assessment (FMEA Approach)
| Potential Failure | Cause | Effect | Prevention |
|---|---|---|---|
| Scaffolding collapse | Overloading or inadequate design | Safety hazard, construction delay | Structural analysis, load testing, inspection |
| Line shape deviation | Inaccurate cable-sling positioning | Aesthetic and structural issues | Survey monitoring, real-time adjustment |
| Transition joint cracking | Differential settlement or shrinkage | Structural integrity concern | Proper reinforcement, controlled concrete placement |
| Cable-sling failure | Overloading or fatigue | Safety hazard | Load rating, inspection, redundancy |
Study Insights and Conclusions
This research provides practical guidance for the construction of CSTC arch bridges in challenging site conditions. The key insight is that the mixed construction method offers a balanced solution that combines the accuracy of formwork-supported construction with the efficiency of cable-sling methods. The finding that the final internal force distribution is largely independent of the construction method is reassuring from a structural safety perspective, as it means that the construction method can be selected based on practical considerations without compromising the final structural performance. However, the superior line shape accuracy achieved with the mixed method is a significant advantage for bridges with stringent geometric requirements, such as those carrying railway or high-speed road traffic. For engineers planning CSTC arch bridge construction, this study demonstrates that the construction method selection should be driven by site conditions, line shape requirements, and construction resources, rather than structural performance concerns alone. The finite element analysis approach used in this study, while not capturing all construction details, provides a reliable framework for evaluating construction method alternatives. Future research could extend this analysis to include time-dependent effects such as concrete shrinkage and creep, which may influence the long-term line shape and internal force distribution of the completed bridge.