Zhuojin Pipe Fitting Co., LtdSurvey and Analysis of Steel Tube Concrete Arch Bridges in China
Literature Overview and Historical Context
This survey paper by Chen Baocun and Yang Yalin from Fuzhou University, published in World Bridges (2006), provides a comprehensive review of steel tube concrete (STC) arch bridges constructed and planned in China. As one of the pioneering studies in this field, it documents the rapid development of STC arch bridge technology in the Chinese infrastructure sector during the early 2000s.
The paper collects data on the number, span, structural form, construction methods, and materials used in existing and planned STC arch bridges, serving as a foundational reference for structural design and construction practices.
Key Findings and Data Summary
The survey reveals several important trends in the development of STC arch bridges:
| Category | Key Observations |
|---|---|
| Number of bridges | Rapid increase from 2000 onwards |
| Span range | Primarily 100–300 m for medium-span applications |
| Structural forms | Single arch, three-hinged arch, two-hinged arch, fixed arch |
| Construction methods | Cantilever construction, suspension cable method, segmental assembly |
| Steel pipe materials | Q235, Q345 carbon structural steel |
| Concrete grades | C30–C50 standard concrete |
| Pipe specifications | Round steel tubes, D/t ratios typically 40–80 |
Steel Pipe Specification and Manufacturing Requirements
From a steel pipe manufacturing perspective, the survey highlights several critical requirements:
Pipe Material Selection
The selection of steel pipe material directly affects the structural performance and durability of the arch rib. Based on the survey data:
| Application | Recommended Steel Grade | Standard Reference | Minimum Yield Strength |
|---|---|---|---|
| Small span (< 150 m) | Q235B | GB/T 3274 | 235 MPa |
| Medium span (150–300 m) | Q345B | GB/T 1591 | 345 MPa |
| Large span (> 300 m) | Q390 or Q420 | GB/T 1591 | 390–420 MPa |
| Corrosive environments | Q345B with coating | GB/T 3274 | 345 MPa |
Pipe Manufacturing Methods
The survey indicates that the primary manufacturing methods for arch rib steel pipes are:
- Seamless pipe: Preferred for high-stress applications due to uniform material properties and absence of longitudinal welds.
- ERW (Electric Resistance Welded): Economical for smaller diameters; requires rigorous weld inspection.
- HFW (High-Frequency Welded): Widely used for medium to large diameters; good mechanical properties.
- LSAW (Longitudinal Submerged Arc Welded): Used for large-diameter pipes (D > 600 mm); requires extensive NDE.
Welding and Fabrication Challenges in Arch Rib Construction
The construction of STC arch bridges involves significant welding activities that present unique challenges:
| Welding Activity | Challenge | Mitigation Strategy |
|---|---|---|
| Pipe segment joint welding | Large diameter, thick wall | Multi-pass SAW with backing ring |
| Arch rib segment splicing | Field welding in difficult positions | Pre-fabrication in shop preferred |
| Connection to bearings | High stress concentration | Full-penetration groove welds |
| Internal stiffener welding | Confined access | Robotic or semi-automatic GTAW |
| Diaphragm attachment | Circumferential weld distortion | Symmetric welding sequence |
The field welding of arch rib segments is particularly challenging due to:
- Positional constraints: Overhead and horizontal welding positions requiring specialized equipment.
- Environmental factors: Weather protection for field welds, particularly in rainy or cold conditions.
- Access limitations: Internal welding for stiffeners and diaphragms requires manholes or robotic systems.
- Residual stress accumulation: Sequential welding of multiple segments can lead to cumulative distortion affecting the arch geometry.
Quality Control and Inspection Protocols
For STC arch bridge applications, the following quality control measures are essential:
| Inspection Stage | Method | Acceptance Criteria |
|---|---|---|
| Incoming pipe material | Mechanical testing, chemical analysis | Per GB/T 8163 or equivalent |
| Pipe surface condition | Visual inspection | No cracks, pits, or scale > 0.5 mm |
| Longitudinal weld (if applicable) | UT + MT | No defects above acceptance level II |
| Circumferential welds | RT or UT | No defects above acceptance level I |
| Post-weld distortion | Geometric measurement | Ovality ≤ 1%, out-of-round ≤ 2 mm |
| Hydrostatic test | Per GB/T 24511 | No leakage at 1.5× design pressure |
| Coating application | DFT measurement | Minimum 200 μm total thickness |
| Concrete placement | Slump test, cube sampling | Per design specification |
Engineering Practice Insights
The survey paper, while primarily focused on structural design and construction methods, provides valuable insights for steel pipe manufacturers and welding engineers. The trend toward larger spans and higher-performance materials indicates increasing demands on pipe quality and welding standards. The adoption of Q345 and higher-grade steels for arch ribs requires careful attention to weldability, particularly the carbon equivalent control (CE ≤ 0.45) and preheating requirements for thick sections.
In my practice, the most critical quality issue in STC arch bridge pipe fabrication is the control of ovality and out-of-roundness after welding. The circumferential welds at segment joints, if not properly controlled, can introduce significant geometric deviations that affect the arch geometry and stress distribution. The use of backing rings with controlled root gap and the application of back-strap welding techniques are essential for achieving the required geometric accuracy. Additionally, the internal diaphragms and stiffeners, which provide critical lateral support to the arch rib, must be welded with full penetration to ensure effective load transfer between the steel pipe and the concrete fill.