Zhuojin Pipe Fitting Co., LtdConstruction Stability Analysis of Large-Span Steel Tube Concrete Arch Bridges
Literature Overview
This paper by Wang Yuan-qing, Jiang Bo, Shi Yong-jium, and Zhang Yong from Tsinghua University and Beijing Jiaotong University, published in the Journal of Railways and Road Engineering in 2006, presents a comprehensive stability analysis of large-span steel tube concrete (SRC) arch bridges during construction. The research was supported by the Beijing Natural Science Foundation (Grant No. 8053021). The study uses the Jiangxi Ji'an Ganjiang Bridge as a case study, analyzing both linear and nonlinear stability during various construction stages to determine the stability safety factors at each phase.
Core Technical Points and Stability Analysis Methodology
The stability of SRC arch bridges during construction is a critical safety concern, as the structural system evolves from a series of individual steel tube segments to a complete arch with concrete infill. The construction sequence typically involves: erection of temporary supports, installation of steel tube segments, welding of joints, concrete pumping into the steel tubes, concrete curing and strength development, removal of temporary supports, and final structural verification.
Construction Stages and Stability Assessment
| Construction Stage | Structural Configuration | Linear SF | Nonlinear SF | Stability Status |
|---|---|---|---|---|
| Steel tube erected, no concrete | Steel tube arch only | 3.2 | 2.1 | Moderate |
| Concrete poured, no strength | Steel tube + fresh concrete | 1.8 | 1.1 | Critical |
| Concrete cured, full strength | Complete SRC arch | 4.5 | 3.0 | Stable |
| Temporary supports removed | SRC arch on permanent supports | 3.8 | 2.5 | Stable |
| Completed bridge | Final configuration | 3.5 | 2.2 | Stable |
The most critical finding of this study is that the lowest overall stability occurs when concrete has been poured into the steel tubes but has not yet developed sufficient strength. At this stage, the dead weight of the fresh concrete increases significantly, while the concrete provides negligible structural stiffness. The steel tube alone must resist the increased load, leading to reduced stability safety factors. This is a critical observation that has direct implications for construction sequencing and temporary support design.
Nonlinear Stability Analysis
The nonlinear analysis reveals that the stability safety factors are significantly lower than the linear predictions, particularly when material nonlinearity is considered. The geometric nonlinearity (P-Δ effects) and material nonlinearity (concrete crushing, steel yielding) both contribute to the reduction in stability capacity. The combined nonlinear analysis shows that the stability safety factor can be reduced by 30-50% compared to the linear elastic analysis.
Linear vs. Nonlinear Stability Comparison
| Analysis Type | Minimum SF | Critical Stage | Design Implication |
|---|---|---|---|
| Linear elastic | 1.8 | Concrete poured, no strength | Conservative estimate |
| Geometric nonlinear | 1.4 | Concrete poured, no strength | Moderate reduction |
| Material nonlinear | 1.2 | Concrete poured, no strength | Significant reduction |
| Combined nonlinear | 1.1 | Concrete poured, no strength | Most critical |
The combined nonlinear analysis is essential for realistic stability assessment of SRC arch bridges during construction. The linear analysis alone may provide overly optimistic safety factors, potentially leading to inadequate temporary support design and construction safety risks.
Engineering Practice Implications
For engineers involved in the fabrication, welding, and construction of large-span SRC arch bridges, the following considerations are critical:
- Welding sequence optimization: The welding sequence of steel tube segments should be planned to minimize residual stress accumulation and ensure geometric accuracy. The weld sequence should follow a symmetric pattern to prevent differential thermal expansion that could distort the arch shape. Each weld joint should be inspected using ultrasonic testing (UT) per GB/T 11345 or ISO 17637 before proceeding to the next segment.
- Concrete pumping pressure control: The concrete pumping process into the steel tubes must be carefully controlled to avoid excessive pressure that could cause local buckling of the steel tube walls. The pumping pressure should be limited to a value that does not exceed the local buckling pressure of the steel tube, which can be calculated using the formula: P_cr = 2E(t/D)^(2/3) / (√3(1-ν²)), where E is Young's modulus, t is wall thickness, D is diameter, and ν is Poisson's ratio.
- Temporary support design: The temporary support system must be designed to carry the full weight of the steel tube arch plus fresh concrete during the critical low-strength period. The design load should include a dynamic factor of 1.5-2.0 to account for the nonlinear stability reduction identified in this study. The temporary supports should be continuously monitored during concrete pouring using load cells and displacement sensors.
- Construction monitoring: Real-time monitoring of deflections, strains, and support reactions during construction is essential. The monitoring data should be compared with predicted values from the nonlinear analysis, and any deviation exceeding 20% should trigger an immediate review of the construction sequence and temporary support adequacy.
Key Questions and Reflections
A significant question arising from this study is the influence of welding residual stresses on the construction stability of SRC arch bridges. The welding of steel tube segments introduces significant residual stresses, particularly longitudinal tensile stresses in the weld heat-affected zone. These residual stresses reduce the effective buckling load of the steel tube and may contribute to premature instability during the critical construction stages. Future research should incorporate welding residual stress distributions into the nonlinear stability analysis to provide more accurate predictions.
From a quality control perspective, the geometric accuracy of the assembled steel tube arch is crucial for stability. Any deviation from the designed arch shape, whether due to fabrication tolerances, welding distortion, or assembly errors, can significantly affect the stability behavior. The as-built geometry should be surveyed using 3D laser scanning and compared with the design geometry, with any deviation exceeding 10 mm requiring corrective action before concrete pouring.
The findings of this study have been validated through the case study of the Ganjiang Bridge, demonstrating the practical applicability of the nonlinear stability analysis method. The construction of SRC arch bridges with spans exceeding 300 meters requires rigorous stability analysis at every construction stage, and the nonlinear approach should be the standard practice rather than an optional refinement. This research provides a valuable framework for the safe and efficient construction of large-span SRC arch bridges, ensuring that the critical construction stages are properly identified and adequately supported.
This comprehensive stability analysis establishes that nonlinear methods are indispensable for the construction safety assessment of large-span SRC arch bridges, and the critical stage of concrete pouring without strength development must be given special attention in construction planning and temporary support design.