Zhuojin Pipe Fitting Co., LtdLine Shape Control Technology Research of Steel Tube Concrete Arch Bridges
Literature Overview
This technical paper by Yao Changrong and Li Yadong (Southwest Jiaotong University, published in 2006 in Highway Traffic Science and Technology) addresses the critical issue of line shape control during the construction of steel tube concrete arch bridges. The study focuses on the relationship between different types of line shapes (design line shape, construction line shape, erection line shape, and final line shape) and proposes a systematic method for calculating and controlling the erection line shape during the cantilever assembly of steel arch rib segments.
Research Background
Steel tube concrete arch bridges are constructed by first erecting the empty steel arch ribs through cantilever assembly or incremental launching, and then filling the steel tubes with concrete to form the final CFST arch rib. The line shape (geometric profile) of the arch is critical for:
- Structural efficiency and load distribution
- Aesthetic appearance
- Long-term performance and durability
- Compliance with design specifications
During construction, the arch rib undergoes several geometric changes:
- The steel arch rib is erected in a specific line shape (erection line shape)
- After concrete filling, the arch rib deforms due to the weight of the concrete and the resulting additional stresses
- The final line shape of the CFST arch rib should match the design line shape
Accurate control of the erection line shape is therefore essential to ensure that the final CFST arch rib achieves the desired design geometry.
Line Shape Relationships
Types of Line Shapes
| Line Shape | Definition | Determination Method |
|---|---|---|
| Design line shape | The intended final geometry of the arch | Structural analysis and design |
| Construction line shape | The geometry during construction phases | Construction planning and calculation |
| Erection line shape | The geometry of the steel arch rib before concrete filling | Back-calculated from design line shape |
| Final line shape | The actual geometry after concrete filling | Surveying and measurement |
Deformation Components
The difference between the erection line shape and the design line shape is composed of several deformation components:
- Self-weight deformation of the steel arch rib: The elastic and plastic deformation of the empty steel arch rib under its own weight
- Concrete self-weight deformation: The additional deformation caused by the weight of the concrete fill
- Thermal deformation: Deformation due to temperature changes during and after construction
- Creep and shrinkage of concrete: Long-term deformation of the concrete fill
- Support settlement: Settlement of the temporary supports during construction
Proposed Calculation and Control Method
Calculation Methodology
The authors propose a systematic method for calculating the erection line shape:
- Step 1: Determine the design line shape from the structural design
- Step 2: Calculate the total deformation components (self-weight, concrete weight, thermal, creep, shrinkage, settlement)
- Step 3: Back-calculate the erection line shape by subtracting the predicted deformations from the design line shape
- Step 4: Verify the calculated erection line shape through structural analysis
- Step 5: Adjust the erection line shape based on construction monitoring data
Key Technical Parameters
The accuracy of the line shape control depends on several key parameters:
| Parameter | Typical Value | Sensitivity |
|---|---|---|
| Steel elastic modulus (E_s) | 206 GPa | High |
| Concrete elastic modulus (E_c) | 30-35 GPa | High |
| Steel arch rib self-weight | Design-dependent | Medium |
| Concrete density | 2400-2500 kg/m³ | Medium |
| Temperature range | -10°C to +40°C | Medium |
| Concrete creep coefficient | 1.5-2.5 | Low-Medium |
| Support settlement | 5-20 mm | Medium |
Construction Control Procedure
The proposed construction control procedure follows a PDCA (Plan-Do-Check-Act) cycle:
- Plan: Calculate the erection line shape and establish control points and tolerances
- Do: Erect the steel arch rib segments according to the calculated erection line shape
- Check: Monitor the actual line shape during and after erection using surveying equipment
- Act: Adjust the erection line shape based on monitoring data and proceed to the next phase
Engineering Practice Applications
Steel Arch Rib Segment Fabrication
From a steel pipe manufacturing perspective, line shape control has several implications:
- Segment length accuracy: The length of each steel arch rib segment must be manufactured to tight tolerances (typically ±2-3 mm) to ensure proper assembly and alignment.
- Segment curvature: Each segment is manufactured with a specific curvature that corresponds to its position in the arch. The curvature accuracy directly affects the assembled line shape.
- Segment connection interfaces: The geometry of the segment connection interfaces (flanges, joints) must be precisely manufactured to ensure proper alignment during assembly.
- Welding distortion control: Welding of segments can cause local distortions that affect the line shape. Pre-welding alignment and post-welding straightening are necessary.
Construction Monitoring
Effective line shape control requires comprehensive construction monitoring:
- Total station surveying at multiple points along the arch
- Leveling measurements for vertical position control
- GPS or GNSS monitoring for overall geometry
- Strain and stress monitoring to verify structural behavior
- Temperature monitoring to account for thermal effects
Study Insights and Reflections
The paper provides a practical and systematic approach to line shape control for CFST arch bridge construction. The key insight is that the erection line shape is not simply the design line shape minus the self-weight deformation, but must account for all deformation components including the concrete fill weight, thermal effects, and long-term deformations.
The PDCA-based construction control procedure is particularly valuable because it provides a feedback loop that allows for adjustments during construction. This is essential because the calculated deformations are predictions based on material properties and boundary conditions that may not perfectly match the actual construction conditions.
From a steel pipe manufacturing perspective, the research emphasizes the importance of dimensional accuracy in steel arch rib segment fabrication. The line shape control method is only as good as the accuracy of the manufactured segments. Any deviation in segment geometry must be accounted for in the erection line shape calculation or corrected during assembly.
The methodology proposed in this paper has been successfully applied to several CFST arch bridge projects in China and can be adapted for other bridge types with similar construction sequences. The systematic approach to line shape control represents a significant advancement in CFST arch bridge construction technology and has contributed to the successful construction of numerous CFST arch bridges with spans exceeding 300 meters.