Zhuojin Pipe Fitting Co., LtdConstruction Plan for Large-Span Steel Tube Concrete Tie-Arch Bridge
Literature Overview
This technical paper, published in the Journal of Dalian University of Technology (2005, Vol. 45, No. 2), presents a comprehensive construction methodology for the Dandong Moon Island Bridge, a large-span steel tube concrete (STC) tie-arch bridge. Authored by Qiu Wenliang and colleagues from the School of Civil and Hydraulic Engineering at Dalian University of Technology, the study addresses the critical challenges of structural stability and stress control during the construction phase of STC arch bridges.
Core Technical Challenges
Large-span STC tie-arch bridges face unique construction challenges due to the sequential nature of steel tube installation, concrete pumping, and structural load transfer. During construction, the structure is in a partially completed state where stress concentrations are elevated and stability safety factors are reduced compared to the final design condition.
| Construction Phase | Key Challenge | Critical Parameter |
|---|---|---|
| Steel tube erection | Temporary lateral stability | Wind load resistance |
| Concrete pumping (lower chords) | Asymmetric loading | Differential settlement |
| Concrete pumping (upper chords) | Arch thrust development | Bearing capacity of temporary supports |
| Cross-beam installation | Load redistribution | Connection integrity |
| Deck concrete placement | Global stability | Composite action |
The stability safety factor during construction is significantly lower than in the completed structure because the tie rods have not yet been tensioned, the arch has not fully developed its thrust, and the structure relies on temporary supports and connections to maintain equilibrium.
Technical Analysis of Construction Scheme
The recommended construction sequence for the Moon Island Bridge involved several key decisions:
- Temporary fixation using sulfur mortar pads: The approach of using sulfur mortar pads to temporarily fix the pile caps to the arch seats provides a controlled release mechanism. Sulfur mortar offers adequate compressive strength for temporary loading while allowing subsequent removal without damaging the concrete surfaces.
- Simultaneous pumping of lower chord tubes: Pumping concrete into both lower chord tubes simultaneously ensures symmetric loading, preventing asymmetric deformation that could compromise structural stability. This is critical because differential concrete placement creates unbalanced moments that the partially constructed structure may not resist.
- Sequential pumping of upper chord tubes: After the lower chords are filled, the upper chord tubes are pumped to complete the arch ribs. This sequence ensures that the lower chords have developed sufficient stiffness to support the additional weight during upper chord filling.
- Segmented construction of cross-beams and deck: The deck concrete is placed in segments to limit the maximum unbalanced load at any time during construction, maintaining the stability safety factor above acceptable thresholds.
Stability Assessment Methodology
The analysis employed a combination of structural finite element modeling and construction stage simulation. Key stability parameters included:
- Lateral buckling resistance of individual steel tubes before concrete filling
- Global stability of the arch system during asymmetric loading phases
- Stress concentration at temporary connection points
- Load path verification during each construction stage
Integration with Engineering Practice
This case study provides a valuable reference for similar STC tie-arch bridge projects. The construction methodology can be adapted for different span lengths and structural configurations, provided that the specific stability characteristics are evaluated through detailed construction stage analysis.
Key lessons for practicing engineers include:
- Always perform construction stage analysis with actual construction sequences, not just the final structural state.
- Symmetric loading is essential during critical construction phases to prevent asymmetric deformation.
- Temporary connections must be designed for the maximum construction loads, which may exceed service loads.
- The pumping sequence must be carefully planned to maintain structural stability throughout the entire construction duration.
- Real-time monitoring of structural response during construction (strain gauges, displacement sensors) is essential to verify that actual behavior matches predictions.
Study Insights and Reflections
The Moon Island Bridge construction study exemplifies the critical importance of integrating structural design with construction methodology. In STC bridge engineering, the construction phase often represents the most critical period for structural safety, as the structure is in a transient state with reduced redundancy and elevated stress concentrations. Engineers must adopt a systems approach that considers material properties, structural configuration, construction logistics, and environmental conditions simultaneously. The sulfur mortar temporary fixation technique, while simple in concept, demonstrates the value of practical engineering solutions that address specific site conditions. Future STC bridge projects should incorporate advanced monitoring systems and real-time structural health assessment to provide additional safety margins during the most vulnerable construction phases.