Dynamic Characteristics Analysis of Xiying Steel Tube Concrete Arch Bridge

Literature Overview

The paper by Zhu Yafei, He Wei, Chen Qiaoyang, and Li Yawei (2016), published in the Journal of Henan University (Natural Science Edition), presents a comprehensive finite element analysis of the Xiying through-type steel tube concrete arch bridge located on the Nanyang-Xichuan section of a provincial highway. The study employs ANSYS as the computational platform to establish a three-dimensional finite element model of the bridge, utilizing the subspace iteration method to extract natural frequencies and mode shapes. The research was funded by the Henan Provincial Basic and Frontier Technology Research Project (152300410241), the Zhengzhou Science and Technology Bureau Development Plan Project (20130844), and the Henan Provincial Education Department Research Plan Project (13B130110).

Core Technical Methodology

The authors adopted a subspace iteration method within the ANSYS framework to solve for the bridge's eigenfrequencies and corresponding mode shapes. The model was validated against measured bridge deck vibration frequencies obtained during field testing. The first-order vertical vibration frequency measured in the field was found to be in close agreement with the theoretical value, confirming the accuracy of the finite element model.

The subspace iteration method is particularly well-suited for large-scale structural models because it iteratively converges on the dominant eigenvalues without requiring the full eigenvalue problem to be solved simultaneously. For a steel tube concrete arch bridge of this scale, the method provides computational efficiency while maintaining sufficient precision for engineering assessment purposes.

Key Findings and Mode Shape Interpretation

The analysis revealed distinct characteristics in the low-order vibration modes of the bridge:

The low-order modes are dominated by either lateral vibration of the arch ribs or vertical bending of the bridge deck system. This pattern reveals that the lateral stiffness of the arch ribs is significantly lower than their vertical stiffness, while the lateral stiffness of the bridge deck system far exceeds its vertical stiffness. This asymmetry in stiffness distribution is a characteristic dynamic performance feature of through-type steel tube concrete arch bridges.

Engineering Practice Implications for Steel Tube Fabrication

From a steel pipe manufacturing perspective, several observations are particularly relevant:

• Arch rib pipe specifications: The arch ribs are typically fabricated from large-diameter steel tubes, often seamless or longitudinally submerged-arc welded pipes conforming to standards such as GB/T 8163 or API 5L. The lateral stiffness deficiency identified in the analysis suggests that the geometric properties (particularly the weak-axis moment of inertia) of the arch rib tubes warrant careful attention during material selection and dimensional tolerance control.
• Welding quality at arch rib joints: The arch ribs are assembled from multiple steel tube segments connected by welded joints. The dynamic response of the structure is sensitive to the stiffness of these joints. Any weld defects, incomplete fusion, or excessive distortion at the butt welds would locally reduce the effective stiffness of the arch rib, potentially altering the natural frequencies and mode shapes. Quality control measures such as ultrasonic testing (UT) and radiographic testing (RT) on all butt welds are essential.
• Concrete infill uniformity: The steel tubes are filled with concrete to form composite arch ribs. The bonding interface between the steel tube inner surface and the concrete is critical for composite action. Poor compaction or voids within the concrete infill would degrade the lateral stiffness of the arch rib, which is already the weakest direction according to the dynamic analysis.

Model Validation and Verification Approach

The validation strategy employed in this study—comparing theoretical frequencies with measured field frequencies—represents a sound engineering practice. The first-order vertical frequency agreement confirms that the finite element model adequately captures the global stiffness characteristics of the bridge. However, from a manufacturing quality perspective, discrepancies in higher-order modes could indicate localized stiffness variations caused by welding defects, geometric deviations, or concrete fill quality issues that would not be apparent in the first-order response.

The study provides a valuable baseline for structural performance evaluation and seismic design. For future projects of similar type, the dynamic analysis results can be used to set acceptance criteria for arch rib fabrication tolerances, weld quality levels, and concrete fill density requirements.

Study Insights and Reflections

This paper demonstrates the importance of integrating structural dynamics analysis with fabrication quality considerations. The finding that lateral stiffness of the arch ribs is the governing dynamic characteristic has direct implications for steel pipe procurement and quality assurance. Engineers should ensure that the weak-axis properties of arch rib tubes meet design requirements and that welding procedures maintain geometric continuity along the arch rib axis. The subspace iteration method proved effective for this application, and its results provide a reliable basis for seismic design decisions. The study reinforces the principle that dynamic performance is not merely a design-stage concern but extends into fabrication, assembly, and quality control throughout the project lifecycle.