Nonlinear Stability Analysis of Long-Span Concrete-Filled Steel Tube Arch Bridge During Construction

Literature Overview

This paper by Xu Kaiming, Zhang Mingzhong, and Wang Ji, published in the Journal of Xi'an University of Architecture and Technology in 2008 (Vol. 40, No. 4, pp. 556-560), presents a nonlinear stability analysis of the Jingyanghe Bridge, a large-span concrete-filled steel tube (CFST) arch bridge with a clear span of 260 m and a deck width of 9 m. The research, funded by the Hubei Provincial Department of Transportation, employs finite element methods using ANSYS to evaluate the elastic buckling, geometric nonlinear, and material nonlinear stability of the bridge during various construction stages. The study is significant for bridge engineers and steel pipe structural engineers who must ensure the structural integrity of large-span CFST arch bridges throughout the complex construction sequence.

Core Technical Content and Methodology

The Jingyanghe Bridge is a deck-type CFST arch bridge characterized by a small width-to-span ratio, which makes stability a critical concern during construction. The construction of such bridges typically involves sequential erection of steel arch ribs, temporary support systems, concrete infilling, and deck installation, each stage presenting unique stability challenges.

The authors employ three levels of stability analysis: elastic buckling analysis, which provides the theoretical upper bound of stability; geometric nonlinear analysis, which accounts for the P-Δ effect and changes in geometry under load; and material nonlinear analysis, which considers the plastic behavior of steel and concrete under high stress states. The finite element model captures the spatial configuration of the arch ribs, the interaction between steel tubes and infilled concrete, and the boundary conditions imposed by temporary supports at each construction stage.

The key finding is that the stability coefficients for all construction stages exceed 10, indicating a low probability of overall instability of the arch ribs. However, the study also reveals that geometric nonlinearity has a relatively minor effect on stability, while material nonlinearity is more significant and cannot be neglected. This is an important distinction because it means that the transition from elastic to inelastic behavior in the steel arch ribs, driven by high compressive stresses during construction, is the primary factor governing stability, rather than geometric imperfections or large displacements.

Process and Standards Analysis

The following table summarizes the stability analysis results and their implications for construction planning:

From a standards perspective, the analysis aligns with the requirements of Chinese codes such as JTG D60 (General Specifications for Design of Highway Bridges and Culverts) and GB 50017 (Standard for Design of Steel Structures), which mandate stability verification for arch bridges under construction loads. The use of ANSYS for spatial finite element modeling is consistent with modern engineering practice, and the inclusion of material nonlinearity reflects the sophisticated understanding of steel-concrete interaction that has developed in recent decades.

For the steel pipe components of the arch ribs, the analysis implicitly assumes that the steel tubes are manufactured to meet the requirements of relevant standards such as GB/T 14976 (Seamless Steel Tubes for Fluid Transport) or SY/T 5037 (Welded Steel Pipe for Oil and Gas Industry). The quality of the steel pipe material, including its yield strength, elongation, and toughness, directly affects the material nonlinear response and thus the stability assessment. Any material defects or inconsistencies in the steel pipe could reduce the actual stability below the predicted values.

Integration with Engineering Practice

In practice, the construction of large-span CFST arch bridges involves a carefully sequenced erection process. The steel arch ribs are typically erected in segments, with temporary cable-stayed supports or temporary truss supports used to carry the weight of the steel and concrete until the arch reaches its final shape and can act as a stable structural element. The stability analysis must be performed for each critical construction stage, including:

1. Initial segment erection with temporary supports
2. Progressive removal of temporary supports
3. Concrete infilling of steel tubes
4. Deck and superstructure installation
5. Final load condition with all permanent loads applied

The finding that material nonlinearity is the dominant factor means that the stress state in the arch ribs during construction must be carefully monitored. If the compressive stresses in the steel tubes approach the yield strength, local buckling of the tube walls can occur, leading to premature failure. This is particularly relevant for the steel pipe fabrication and welding processes, as welding residual stresses and distortion can create localized stress concentrations that reduce the buckling resistance of the tube walls.

From a welding quality control perspective, the welds in the arch rib steel tubes must be inspected thoroughly to ensure full penetration and the absence of defects such as lack of fusion, porosity, or cracks. Any weld defect can serve as a stress concentrator that initiates local buckling under compressive loading. Non-destructive testing methods such as ultrasonic testing (UT), radiographic testing (RT), and magnetic particle testing (MT) should be employed to verify weld integrity in accordance with relevant standards such as GB/T 11345 or ISO 17640.

Key Questions and Reflections

The study raises an important question: how do manufacturing defects and weld quality in the steel arch ribs affect the predicted stability coefficients? The finite element model likely assumes perfect material properties and idealized geometry, but in reality, steel pipes may have thickness variations, residual stresses from manufacturing, and weld defects that reduce the actual stability below the theoretical predictions. Future research should incorporate statistical models of material variability and weld quality into stability analyses to provide more realistic safety assessments.

Additionally, the study does not address the effect of construction tolerances on stability. In practice, the erected arch ribs may deviate from the ideal geometric shape due to erection errors, thermal effects, and support settlement. These deviations can significantly affect the stability, particularly for slender arch ribs with low width-to-span ratios. The integration of construction monitoring data with stability models could provide a more accurate assessment of the actual structural behavior during construction.

Study Insights and Conclusions

The nonlinear stability analysis of the Jingyanghe Bridge provides valuable guidance for the construction planning of large-span CFST arch bridges. The conclusion that stability coefficients exceed 10 for all construction stages offers confidence in the structural safety, while the finding that material nonlinearity is the dominant factor highlights the importance of accurate material characterization and stress monitoring during construction. For steel pipe engineers and fabricators, this study underscores the critical role of material quality and weld integrity in ensuring the stability of CFST arch bridges. The integration of advanced finite element analysis with rigorous material and weld quality control is essential for the safe and successful construction of these complex structures. This work represents a significant contribution to the field of bridge engineering and provides a methodological framework that can be adapted for similar large-span CFST structures.