Dynamic Analysis of Through-Truss CFST Arch Bridges Considering Hanger Rope Fracture Process

Literature Overview

This study by Wu Qingxiong and colleagues from Fuzhou University, published in the Journal of Fuzhou University (Natural Science Edition) in 2023, addresses a critical safety concern in through-truss concrete-filled steel tube (CFST) arch bridges: the progressive collapse mechanism triggered by hanger rope fracture. The authors collected and analyzed the main parameters of 62 through-truss CFST arch bridges to construct six standard arch bridge models with different spans. Using MSC.Marc finite element software, they simulated the full fracture process of hanger ropes in a scaled experimental model, discussed dynamic coefficient calculation methods, and determined the dynamic coefficient values for remaining hangers and stiffening longitudinal beams when short, second-short, and long hangers fracture respectively. This work is particularly significant for engineers involved in the design, inspection, and maintenance of large-span arch bridge structures where steel pipe components serve as primary load-bearing elements.

Core Technical Points and Interpretation

Finite Element Simulation Methodology

The study employs MSC.Marc to simulate the complete hanger fracture process, which is a challenging nonlinear dynamic problem. The maximum error between simulation results and experimental measurements is only 11.25%, demonstrating acceptable accuracy for engineering applications. The simulation captures the entire sequence from fracture initiation through dynamic redistribution of loads to adjacent structural members. For engineers familiar with steel pipe manufacturing and structural analysis, this approach highlights the importance of understanding how steel pipe arch ribs respond to sudden loss of load paths, particularly at welded connections and splice joints where residual stresses from pipe fabrication processes may compound the dynamic response.

Dynamic Coefficient Determination

The key finding is that when dynamic coefficient values of 1.75 for remaining hangers and 1.80 for stiffening longitudinal beams are adopted, static calculation results are essentially consistent with the maximum values from dynamic calculations, and the results are on the safe side. This provides a practical engineering tool for simplified design checks.

Location of Maximum Dynamic Response

The study reveals that when any hanger fractures, the maximum dynamic response in both the arch rib and stiffening longitudinal beam occurs at the cross-section corresponding to the fractured hanger's position. For remaining hangers, the adjacent hangers to the fractured one experience the maximum dynamic response. This spatial distribution pattern is critical for inspection prioritization and damage assessment after any hanger failure event.

Engineering Practice Implications

For steel pipe manufacturing and welding engineers, the implications are multi-layered. First, the quality of welded connections in the stiffening longitudinal beams and arch ribs directly affects the dynamic load redistribution capacity. Any weld defects—porosity, incomplete fusion, or lack of penetration—could become initiation points for progressive failure under dynamic loading conditions. Second, the residual stress state in steel pipes used for arch ribs, influenced by manufacturing processes such as hot rolling, cold bending, and welding, affects the overall dynamic response characteristics. Third, the stiffening longitudinal beams in through-truss bridges often use welded steel pipe or box sections, and their weld quality is paramount given that they must absorb dynamic loads with coefficients approaching 1.80.

The study's recommendation to adopt dynamic coefficients of 1.75 and 1.80 in static analysis provides a practical safety margin that can be incorporated into design codes and inspection standards. However, engineers should note that these values represent an average across different span ranges and hanger fracture locations, and site-specific dynamic analysis may be warranted for critical bridges.

Key Questions and Reflections

A significant question arises regarding the applicability of these dynamic coefficients to bridges with different structural configurations, such as those using spiral-welded or submerged-arc welded steel pipes for arch ribs, where the weld geometry and heat-affected zone characteristics differ from seamless or ERW pipe. Additionally, the study does not extensively address the cumulative fatigue effects on remaining hangers and longitudinal beams following a fracture event, which is a concern for long-term operational safety. Engineers should consider incorporating fracture mechanics-based assessments for critical hanger connections in bridges with spans exceeding 300 meters, where the consequences of progressive collapse are most severe.

Study Insights and Conclusions

This research provides valuable quantitative data for the dynamic assessment of through-truss CFST arch bridges following hanger rope fracture. The established dynamic coefficient values of 1.75 and 1.80 offer a practical and conservative approach for simplified design verification, while the finite element methodology validated against experimental data provides a pathway for more detailed site-specific analyses. For steel pipe and welding professionals, the key takeaway is that the integrity of welded connections in arch ribs and stiffening beams is not merely a static strength issue but a dynamic safety-critical consideration that demands rigorous quality control throughout fabrication and installation. The work underscores the need for continued research on the interaction between manufacturing-induced residual stresses, weld quality, and dynamic structural response in large-span steel pipe structures.