Dynamic Analysis of Under-Ribbed CFST Arch Bridge Considering Hanger Rupture Process

Literature Overview

The paper by Wu Qingxiong et al. (2023), published in Journal of Fuzhou University (Natural Science Edition), Volume 51, Issue 3, presents a systematic investigation into the dynamic behavior of under-ribbed concrete-filled steel tube (CFST) arch bridges under hanger rupture scenarios. The authors collected and analyzed the main parameters of 62 existing under-ribbed CFST arch bridges to construct six standard arch bridges with different spans. Using MSC.Marc finite element software, the full process of hanger rupture in a scaled experimental model was simulated, and the dynamic amplification factors (DAF) for residual hangers and stiffening longitudinal beams were determined for three rupture locations: short hanger, sub-short hanger, and long hanger. The maximum simulation error was only 11.25%, demonstrating good reliability of the numerical model. This work is particularly relevant to pipe and bridge structural engineers because the arch ribs in these bridges are typically fabricated from large-diameter steel tubes, often seamless or longitudinally welded, and the hanger connection nodes involve critical welding and bolted connections that must withstand dynamic overloads during rupture events.

Core Technical Points and Methodology

The study employs a two-stage approach: first, a scaled physical model test is conducted to capture the dynamic response during hanger rupture, and second, a full-scale finite element simulation using MSC.Marc is validated against the test data. The key methodology involves modeling the hanger rupture as a progressive failure event where the hanger is released in stages to simulate the dynamic unloading process. The authors discuss the calculation method for the dynamic amplification factor, which is defined as the ratio of the maximum dynamic response (displacement, stress, or force) to the corresponding static response under the same loading condition.

The following table summarizes the key findings regarding dynamic amplification factor values for different span configurations:

The authors recommend that when the dynamic amplification factors for residual hangers and stiffening longitudinal beams are taken as 1.75 and 1.80 respectively, the static analysis results are essentially consistent with the maximum dynamic calculation values, and the results are on the safe side. This is a practically important finding because it allows engineers to avoid complex dynamic analyses in many design scenarios and instead use simplified static methods with appropriate amplification factors.

Key Findings and Engineering Implications

The study reveals several important patterns regarding the dynamic response distribution. First, for each hanger rupture scenario, the maximum dynamic response in the arch rib and stiffening longitudinal beam cross-sections occurs at the position corresponding to the ruptured hanger. Second, among the residual hangers, the adjacent hangers to the ruptured one exhibit the largest dynamic response, which is consistent with the load redistribution mechanism. This means that in the event of a single hanger failure, the neighboring hangers bear the greatest additional dynamic loads, and their connections and welding details must be designed accordingly.

From a steel pipe fabrication and welding perspective, this study has several direct implications. The arch ribs of under-ribbed CFST bridges are typically fabricated from large-diameter steel tubes, often in the range of 600 mm to 1500 mm in outer diameter, with wall thicknesses of 20 mm to 60 mm. These tubes are commonly produced by seamless or longitudinally submerged arc welding (LSAW) processes. The hanger-to-arch rib connection nodes involve complex welding details, including gusset plates welded to the tube surface, which are susceptible to dynamic fatigue and brittle fracture under the sudden load redistribution caused by hanger rupture. The recommended dynamic amplification factors of 1.75 and 1.80 should be incorporated into the design of these critical welded connections, ensuring that the weld details meet the ductility and toughness requirements specified in standards such as GB/T 19804, AWS D1.1, or ISO 15614.

The simulation error of 11.25% between the MSC.Marc model and the scaled test is acceptable for engineering purposes, but it highlights the importance of accurate material constitutive models and proper representation of the hanger rupture process in finite element analysis. In practice, engineers should ensure that the material models account for strain rate effects, particularly for the steel tubes and hangers, as the dynamic loading conditions during hanger rupture involve strain rates significantly higher than those in static loading.

Connection to Welding Quality and Defect Control

The dynamic amplification factors derived in this study directly influence the allowable stress levels in the welded connections of the arch bridge. In the context of welding quality control, this means that the following considerations are essential:

The adjacent hangers, which experience the largest dynamic response after a hanger rupture, should be designed with enhanced weld details and possibly larger cross-sections to accommodate the dynamic overload. The stiffening longitudinal beams, which have a higher recommended DAF of 1.80, also require careful attention to their fabrication and welding quality, particularly at the joints where the beams connect to the arch ribs and hangers.

Study Insights and Reflections

This paper provides a valuable engineering tool for the design of under-ribbed CFST arch bridges, particularly in terms of robustness and redundancy against hanger failure. The recommendation of DAF values of 1.75 and 1.80 simplifies the design process significantly, as engineers can use static analysis methods with these amplification factors rather than performing full dynamic analyses. However, it is important to note that these values are derived from a specific set of bridge configurations and may not be universally applicable to all bridge types. Engineers should exercise judgment and consider the specific structural characteristics of their projects when applying these recommendations.

From a metallurgical and welding engineering perspective, the study underscores the importance of designing for dynamic loading conditions in steel tube structures. The arch rib tubes and hanger connection welds must be qualified for dynamic loading, which may require additional testing beyond standard static qualification procedures. The strain rate sensitivity of the steel materials used in the tubes and welds should be evaluated, and the welding procedures should be selected to minimize residual stresses and avoid brittle fracture mechanisms.

Summary

This literature provides a comprehensive framework for evaluating the dynamic behavior of under-ribbed CFST arch bridges under hanger rupture scenarios, offering practical dynamic amplification factor recommendations that can be directly applied in engineering design. The findings are particularly relevant to steel pipe fabrication and welding quality control, as the critical welded connections in these bridges must be designed to withstand dynamic overloads with appropriate safety margins.