Geometric Nonlinear Analysis of Arch Rib Hoisting for CFST Arch Bridges

Literature Overview

This 2003 paper by Zhang Mingyuan, Wang Xueguo, Jiang Zhixue, and Lu Zhe'an, published in the Journal of Wuhan University of Technology (Vol. 25, No. 9), addresses the geometric nonlinear behavior during the hoisting of arch ribs in large-span concrete-filled steel tube (CFST) arch bridges. The authors developed a geometric nonlinear static analysis program for cable-beam-rod plane structural systems and applied it to simulate the arch rib hoisting process of the Nanlidu Bridge in Enshi Prefecture. The research was supported by the Hubei Provincial Science and Technology Project (20011g0037).

Core Technical Findings

The study focuses on the geometric nonlinear problem inherent in the arch rib hoisting process of large-span CFST arch bridges. The key contribution is the development of a specialized geometric nonlinear static analysis program capable of handling the coupled behavior of cables, beams, and rods in a plane structural system. The forward algorithm was employed as the basis for the analysis, incorporating construction control theory.

Process and Standards Analysis

The geometric nonlinear analysis is essential for arch rib hoisting because the arch rib undergoes significant geometric changes during the erection process. As the arch rib is lifted from its initial position to its final position, the load path changes continuously, and the structural behavior transitions from a cantilever or suspension system to a true arch. Linear analysis cannot capture these effects, leading to potentially unsafe design decisions.

The forward algorithm is a common approach in construction stage analysis, where the structure is analyzed in discrete stages corresponding to actual construction sequences. This approach is consistent with the requirements of GB 50010 (Code for Design of Concrete Structures) and JTJ 041 (Specifications for Design of Highway Bridges and Culverts), which emphasize the importance of construction stage analysis for large-span bridges.

The custom-developed program for cable-beam-rod plane systems is a significant technical contribution. Commercial finite element software often struggles with the geometric nonlinear behavior of cable structures because cables cannot resist compression and their stiffness is highly dependent on the tension level. The specialized program likely employs a tension-only cable element formulation with appropriate convergence criteria.

Integration with Engineering Practice

In practice, the arch rib hoisting process for CFST arch bridges is one of the most critical and complex construction activities. The analysis results directly inform the construction control strategy, including the sequence of lifting operations, the tensioning of temporary cables, and the monitoring of deflections and stresses during erection.

For steel pipe suppliers, the hoisting analysis has direct implications for the design of the steel tubes used in the arch rib. The tubes must be designed to withstand not only the final service loads but also the temporary loads during construction. The geometric nonlinear analysis provides the most accurate prediction of these temporary loads, ensuring that the steel tubes have adequate strength and stiffness at all construction stages.

The study also highlights the importance of construction monitoring. Real-time monitoring of deflections, stresses, and cable tensions during hoisting allows for comparison with predicted values and enables timely adjustments to the construction procedure. This is consistent with the FMEA (Failure Mode and Effects Analysis) approach, where potential failure modes during construction are identified and mitigated through monitoring and control measures.

The Nanlidu Bridge case study provides a practical example of the application of the analysis method. Engineers involved in similar projects can use the methodology as a reference, adapting it to the specific geometry, span, and construction method of their project. The experience gained from this project can be applied to future CFST arch bridge projects, improving the accuracy and reliability of construction stage analysis.

Key Questions and Reflections

The study raises the question of whether the plane structural system assumption is sufficient for practical applications. In reality, the arch rib hoisting process involves three-dimensional effects, particularly when the arch rib has a significant horizontal curve or when the temporary support system is asymmetric. A three-dimensional geometric nonlinear analysis would provide more accurate predictions but at the cost of increased computational complexity.

Another important consideration is the material behavior of the CFST arch rib during hoisting. The concrete in the arch rib may not have reached its design strength at the time of hoisting, particularly for long-span bridges where the concrete curing period is extended. The interaction between the steel tube and the concrete, which is a key feature of CFST structures, may not be fully developed during the construction phase. The study's focus on geometric nonlinearity is appropriate, but the interaction with material nonlinearity should also be considered for a complete analysis.

The custom-developed program, while powerful for the specific application, may not be readily available to all engineers. The increasing availability of commercial software with robust geometric nonlinear capabilities may reduce the need for specialized programs in the future. However, the understanding of the underlying physics and the ability to develop specialized analysis tools remain valuable skills for engineers working on complex bridge projects.

Study Insights and Implications

This paper represents an important contribution to the field of construction stage analysis for CFST arch bridges. The development of a specialized geometric nonlinear analysis program demonstrates the need for tailored analytical tools when dealing with complex construction processes. The application to the Nanlidu Bridge provides a validated case study that can serve as a reference for future projects.

For engineers involved in the design and construction of CFST arch bridges, the key takeaway is that geometric nonlinear analysis is not optional but essential for safe and efficient construction. The results of such analysis should be integrated into the construction control plan and used to guide real-time monitoring and decision-making during the hoisting process. The study also underscores the importance of collaboration between structural engineers, construction engineers, and steel pipe manufacturers to ensure that the design, fabrication, and construction of CFST arch bridges are all based on accurate and reliable analysis.