Zhuojin Pipe Fitting Co., LtdConstruction Analysis and Control of Steel Tube Concrete Tie-Arch Bridges
Project Background and Research Significance
The paper by Li Jie, Chen Huai, and Feng Guanjie from Zhengzhou University presents a detailed construction analysis and control study for a steel tube concrete (SRC) tie-arch bridge on the South-to-North Water Transfer Central Route project. Published in Journal of Zhengzhou University (Science Edition) (Vol. 48, Issue 1, 2016, pp. 110–115), and supported by the Henan Provincial Basic and Frontier Technology Research Program (162300410264), this research addresses the critical challenges of construction monitoring and control for large-span SRC tie-arch bridges. The study combines finite element numerical analysis with on-site construction monitoring to ensure structural safety and quality throughout the construction process.
Structural System and Construction Sequence
A tie-arch bridge consists of an arch rib that transfers loads to the piers, a deck (tie beam) that resists the horizontal thrust from the arch, and hanger rods that connect the arch to the deck. In the SRC configuration, the arch rib is constructed as a steel tube filled with concrete, combining the high strength and ductility of steel with the compressive capacity and durability of concrete. The construction sequence typically involves:
- Erection of the steel tube arch rib segments
- Concrete infill of the arch rib steel tubes
- Installation of the deck structure (tie beam)
- Tensioning of the hanger rods
- Final adjustment and quality verification
Construction Phase Analysis
| Construction Phase | Primary Structural Action | Key Monitoring Parameters |
|---|---|---|
| Arch rib erection | Self-weight and assembly loads | Arch deformation, node forces |
| Concrete infill | Increased arch self-weight | Arch stress, deformation |
| Deck installation | Dead load transfer through hangers | Hanger forces, deck deflection |
| Hanger tensioning | Load redistribution and stress adjustment | Hanger tension, arch thrust, deck line shape |
| Final state | Full service loads | Overall line shape, force distribution |
The finite element model was established using MIDAS/Civil software, a specialized structural analysis program widely used in bridge engineering. The model incorporated the nonlinear material behavior of steel and concrete, the geometric nonlinearity associated with large deformations, and the sequential construction effects. Each construction stage was modeled as a separate analysis step, with the results of the previous stage carried forward as initial conditions for the subsequent stage.
Numerical Analysis Results
The numerical analysis revealed that the structural deformations during construction remained within acceptable limits throughout all construction phases. The stress distribution in the arch rib, tie beam, and hanger rods satisfied design code requirements at every stage. The analysis confirmed that the SRC arch rib exhibited favorable structural behavior, with the steel tube providing initial stiffness during the erection phase and the concrete infill contributing additional compressive capacity and stiffness after curing.
Key Analysis Findings
| Parameter | Analysis Result | Design Requirement | Status |
|---|---|---|---|
| Maximum arch deflection | Within acceptable range | Code-specified limits | Satisfied |
| Arch rib stress | Below allowable stress | Material design strength | Satisfied |
| Hanger tension (dead load) | Within design range | Hanger capacity | Satisfied |
| Deck deflection | Within serviceability limits | Span ratio limits | Satisfied |
The analysis also examined the hanger tension distribution under different construction scenarios. An important finding was that the dead load hanger tension (the tension in hangers due to the self-weight of the structure alone) could serve as a reliable reference for the final hanger tension adjustment. This finding has significant practical implications for construction control, as it simplifies the tensioning procedure by providing a clear target value that accounts for the actual construction sequence.
Construction Control Strategy
The construction control employed an adaptive control method, which involves comparing measured structural responses with predicted values at each construction stage and making adjustments as needed. This approach is particularly suitable for SRC tie-arch bridges because the stiffness of the arch rib and tie beam is relatively flexible compared to conventional reinforced concrete arches, leading to greater sensitivity to construction sequence variations and environmental effects.
Adaptive Control Methodology
| Step | Action | Purpose |
|---|---|---|
| 1 | Predict structural response for next construction phase | Establish expected baseline |
| 2 | Execute construction phase | Implement planned activity |
| 3 | Measure actual structural response | Capture real-world behavior |
| 4 | Compare measured vs. predicted values | Identify deviations |
| 5 | Adjust subsequent phase parameters if needed | Correct deviations |
The control strategy recommended using the dead load hanger tension as the target tension value for hanger adjustment. After the structure reaches its final configuration, the hanger tensions were fine-tuned based on the measured line shape of the tie beam and arch rib. This two-step approach ensures that both the force distribution and the geometric shape meet design requirements.
The on-site monitoring results confirmed that the final bridge line shape and force distribution satisfied design requirements. The final hanger tensions were found to be in close agreement with the dead load hanger tensions predicted by the numerical analysis, validating the proposed control strategy.
Engineering Practice Considerations
Monitoring Instrumentation
Effective construction monitoring requires a comprehensive instrumentation plan. For SRC tie-arch bridges, the monitoring system should include:
- Strain gauges on the arch rib at critical sections to measure stress levels
- Displacement transducers at arch crown, haunches, and springings to track deformation
- Load cells or strain gauges on hanger rods to measure tension forces
- Total station or GNSS for overall line shape monitoring
- Temperature sensors to account for thermal effects on structural response
Quality Control for SRC Arch Rib
The concrete infill process for the steel tube arch rib is a critical construction activity that directly influences the structural performance. Key quality control measures include:
- Verification of steel tube cleanliness and internal surface preparation before concrete placement
- Control of concrete mix design, including slump, air content, and admixture dosage
- Use of appropriate concrete pumping and vibration methods to ensure complete fill without voids
- Monitoring of concrete curing conditions, particularly temperature and moisture
- Non-destructive testing of the concrete infill to verify fill quality and detect voids
Key Reflections and Study Insights
This study demonstrates the importance of integrating numerical analysis with on-site monitoring for the successful construction of complex bridge structures. The adaptive control approach proved effective in managing the construction process and ensuring that the final structure met design expectations. The finding that dead load hanger tensions serve as reliable target values for hanger adjustment is a practical insight that simplifies the construction control procedure.
The research also highlights the unique characteristics of SRC tie-arch bridges compared to conventional reinforced concrete arch bridges. The steel tube concrete arch rib provides higher initial stiffness during construction, which is advantageous for the erection phase. However, the relatively flexible nature of the SRC system compared to solid reinforced concrete arches requires more careful construction control to manage deformations and force distributions.
From a welding and fabrication perspective, the quality of the steel tube arch rib segments is paramount. The steel tubes must be manufactured to precise dimensional tolerances, and the segment joints must be designed and fabricated to ensure proper load transfer. Welding procedures for the steel tube segments, including the end plates and connection details, must be qualified through weld procedure qualification testing and documented in welding procedure specifications. Non-destructive testing of critical welds, including ultrasonic testing and magnetic particle testing, is essential to verify weld integrity.
Summary
The construction analysis and control study for the SRC tie-arch bridge on the South-to-North Water Transfer Central Route project provides a comprehensive case study in bridge construction engineering. The integration of finite element analysis with adaptive construction control demonstrated the effectiveness of this approach in managing complex construction sequences and ensuring structural safety. The proposed strategy of using dead load hanger tensions as target values for hanger adjustment offers a practical and efficient control method for SRC tie-arch bridges. For practicing bridge engineers, this study reinforces the importance of thorough numerical modeling, comprehensive monitoring instrumentation, and systematic adaptive control in the construction of large-span arch bridges.