Nonlinear Analysis of Cable Hoisting for Large-Span CFT Arch Bridges

Literature Overview

The paper by Dai Peng, Xie Gongyuan, Hao Xianwu, and Zhou Yongchao, published in the Journal of Wuhan University of Technology (2007, Vol. 29, No. 2, pp. 114–117), presents a nonlinear analysis methodology for cable hoisting of large-span steel tube concrete (CFT) arch bridges. The research was conducted at the Shaanxi Key Laboratory of Bridge and Tunnel Engineering, Chang'an University, with collaboration from the Hubei Provincial Transportation Engineering Quality Supervision Station. The study established a spatial finite element model using the moving coordinate iteration method to account for geometric nonlinearity, and developed an optimization model for cable hoisting forces based on optimization theory.

Core Technical Content

Nonlinear Analysis Methodology

The cable hoisting process for large-span arch bridges involves significant geometric nonlinearity due to large displacements and changes in structural configuration. The authors employed the moving coordinate iteration method to account for these nonlinear effects, which is essential for accurate prediction of structural behavior during the hoisting process. The conventional linear analysis approach is insufficient for this application because:

Cable Hoisting Force Optimization

The authors developed an optimization mathematical model for cable hoisting forces based on optimization theory. The objective function minimizes the deviation between the actual and target positions of control points during the hoisting process. The constraints include cable force limits, structural stress limits, and geometric compatibility requirements. The optimization ensures that the cable forces are distributed efficiently to achieve the target structural configuration with minimal deviation.

Engineering Case Study: 368 m Span CFT Arch Bridge

The methodology was validated using a 368 m span CFT arch bridge as an engineering case study. The forward analysis method was employed to simulate the entire hoisting process step by step, accounting for the progressive assembly of arch rib segments and the corresponding changes in structural configuration.

Welding and Assembly Considerations

Field Welding of Arch Rib Segments

The cable hoisting process requires that arch rib segments be welded together in the elevated position during the hoisting operation. This presents unique challenges:

The welding quality at elevated positions is critical because any defects would be difficult to repair and could compromise the structural integrity of the arch rib. The cable hoisting process requires that welds be inspected immediately after completion, before the next segment is hoisted, to ensure that defects are detected and repaired promptly.

Steel Tube Specifications for Arch Ribs

Construction Process Analysis

Step-by-Step Hoisting Sequence

The forward analysis method simulates the hoisting process in discrete steps, each corresponding to the hoisting and welding of one or more arch rib segments:

1. Initial setup: Cable system installation and tensioning
2. First segment hoisting: Initial arch rib segment raised to position
3. Segment welding: Field welding of segment joints
4. Concrete filling: CFT filling of completed segments
5. Subsequent segments: Progressive hoisting and assembly
6. Final configuration: Complete arch rib structure achieved

At each step, the nonlinear analysis updates the structural configuration and recalculates the cable forces required to maintain the target geometry. The optimization model adjusts the cable forces to minimize deviations at control points.

Quality Control During Hoisting

Study Insights and Reflections

The nonlinear analysis methodology presented in this paper is essential for the safe and efficient hoisting of large-span CFT arch bridges. The geometric nonlinearity that becomes significant in large-span structures cannot be ignored, and the moving coordinate iteration method provides a practical approach to accounting for these effects. The optimization of cable hoisting forces is particularly valuable because it reduces the number of adjustment iterations during actual construction, saving time and resources.

From a welding perspective, the elevated welding operations during cable hoisting represent a significant quality challenge. The 6G positional welding requires highly skilled welders and careful process control. The residual stresses from welding can interact with the cable hoisting forces, potentially causing unexpected distortions in the arch rib. The nonlinear analysis should ideally incorporate welding residual stresses to provide a more accurate prediction of the structural configuration.

The validation with the 368 m span bridge case study demonstrates the practical applicability of the methodology. The small deviations at control points indicate that the nonlinear analysis and force optimization approach are effective for real-world applications. However, the study could benefit from additional discussion on the sensitivity of the results to variations in cable force, welding quality, and concrete filling density, which are all sources of uncertainty in practice.

Summary

This research provides a robust nonlinear analysis framework for cable hoisting of large-span CFT arch bridges, validated with a 368 m span engineering case. The moving coordinate iteration method and cable force optimization model offer practical tools for construction planning and execution. The methodology ensures that geometric nonlinearity is properly accounted for, leading to accurate predictions of structural behavior during the hoisting process. Engineers should integrate this analysis with rigorous welding quality control and concrete filling verification to ensure the successful construction of large-span CFT arch bridges. The combination of nonlinear analysis, force optimization, and quality control forms a comprehensive approach to managing the complex construction process of these structures.