Seismic Response Analysis of Large-Span Concrete-Filled Steel Tube Arch Bridges

Literature Overview

The paper by Wu Naishen, Wang Yuansheng, and He Tao (2009), published in the Journal of Zhengzhou University (Engineering Science), presents a finite element analysis of the seismic response of a large-span concrete-filled steel tube (CFST) arch bridge. The study establishes a structural model using the finite element method to compute the natural vibration characteristics, then applies time-history analysis to evaluate the dynamic properties and seismic response considering the effects of hanger tension and initial arch stress. The results compare the seismic behavior with and without these initial stress effects, ultimately concluding that the initial stress has a minor influence on the mechanical performance of the arch ribs and that the bridge meets design requirements with good seismic performance.

Core Technical Points

From a steel pipe engineering perspective, the key technical contributions of this paper revolve around the interaction between the steel tube arch rib and the infill concrete under dynamic seismic loading. The arch ribs in CFST arch bridges are typically fabricated from high-strength steel tubes, often conforming to standards such as GB/T 14976 or API 5L, with wall thicknesses ranging from 12 mm to 40 mm depending on span and load requirements. The concrete infill provides lateral confinement to the steel tube, enhancing the ductility and energy dissipation capacity of the arch rib under cyclic loading.

The study highlights that the initial stress state in the arch rib—arising from the pre-tensioned hangers and the self-weight of the structure—does not significantly alter the fundamental dynamic characteristics of the bridge. This is a critical finding for engineers involved in the fabrication and welding of CFST arch ribs, as it suggests that the residual stresses introduced during the welding and forming of the steel tube segments do not critically compromise the seismic performance of the completed structure, provided the welding quality meets the relevant standards.

Welding and Fabrication Implications

The fabrication of large-span CFST arch bridge ribs involves the welding of large-diameter steel tubes, typically using submerged arc welding (SAW) or flux-cored arc welding (FCAW) for longitudinal seams. The weld quality directly affects the fatigue and seismic performance of the arch rib. The following table summarizes the typical welding parameters and quality requirements for such applications:

The study's conclusion that initial stress has limited effect on seismic performance is reassuring for fabrication engineers, but it does not eliminate the need for strict weld quality control. Residual stresses from welding can still contribute to local buckling of the steel tube wall under compressive loading, particularly in the arch rib segments subjected to high axial forces during seismic events.

Engineering Practice and Reflections

In practice, the fabrication of CFST arch bridge ribs involves several critical steps: tube forming and welding, segment assembly, concrete pumping and compaction, and final joint welding. Each step introduces potential quality risks that must be managed through systematic quality control procedures. The finite element model used in the study assumes idealized material properties and perfect bond between the steel tube and concrete, which may not fully capture the real-world behavior affected by welding defects, concrete voids, or incomplete compaction.

The comparison between models with and without initial stress effects is particularly relevant for engineers who must decide on the level of analytical sophistication required for seismic assessment. For routine design verification, simplified models that neglect initial stress may be acceptable, but for critical bridges or those in high-seismic zones, the inclusion of initial stress effects is recommended to ensure a more conservative and reliable assessment.

This paper provides valuable guidance for the seismic design and fabrication quality control of CFST arch bridges. Engineers involved in the manufacturing of steel tube arch ribs should ensure that welding procedures are qualified in accordance with GB/T 19866 and that the final products undergo comprehensive non-destructive testing to guarantee the structural integrity required for seismic resistance.