Equivalent Static Calculation Method for CFST Arch Bridges Under Hanger Rupture Dynamic Action

Literature Overview

The research by Chen Kangming and colleagues, published in the China Civil Engineering Journal (2023, Vol. 56, No. 6), presents an equivalent static calculation method that accounts for the dynamic effects of hanger rupture in mid-span and lower-deck concrete-filled steel tube (CFST) arch bridges. This work, supported by the National Key R&D Program (2017YFE0130300), the National Natural Science Foundation (52078137, 51678154), and the Fujian Provincial Natural Science Foundation Distinguished Young Scholars Program (2019J06009), addresses a critical structural safety issue in cable-stayed arch bridge design. The study combines large-scale experimental testing with finite element simulation to establish practical dynamic coefficients for equivalent static analysis.

Core Technical Content

Experimental Methodology

A large-scale scaled model of a 20-meter span lower-deck CFST arch bridge was designed and constructed. A novel electromagnetic hanger rupture trigger device was developed to achieve instantaneous hanger failure within 0.1 seconds, accurately simulating real-world hanger rupture scenarios. The experimental program focused on measuring the dynamic response of the remaining bridge structure following hanger rupture, including longitudinal beam displacements, stresses, and arch rib responses.

Finite Element Modeling

ANSYS/LS-DYNA was employed to establish a finite element model capable of simulating the hanger rupture process. The model was validated through comparison with experimental results, demonstrating good agreement between numerical and experimental predictions. The validated model was then used for parametric studies on 11 different span standard CFST arch bridges.

Dynamic Coefficient Determination

Key Experimental Findings

1. The electromagnetic rupture trigger achieves hanger failure within 0.1 seconds, providing an accurate simulation of actual rupture dynamics.
2. Hanger rupture has a significantly greater impact on longitudinal beam displacement and stress than on arch rib response.
3. Longer hanger rupture causes larger displacement and stress effects on both longitudinal beams and arch ribs.
4. The rupture of the second-shortest hanger has the greatest impact on adjacent hanger cable forces.

Technical Analysis and Design Implications

Dynamic Amplification Mechanism

When a hanger ruptures, the sudden release of prestress creates a dynamic load that propagates through the bridge structure. The dynamic coefficient amplifies the static redistribution of forces to account for this dynamic effect. The difference between longitudinal beam and hanger dynamic coefficients in lower-deck bridges (1.8 vs. 1.7) reflects the different dynamic characteristics of these components under rupture-induced loading.

Structural Robustness Assessment

The finding that hanger rupture primarily affects the longitudinal beam system rather than the arch ribs suggests that the arch rib serves as a robust load-bearing element that can effectively redistribute loads following hanger failure. This characteristic is particularly advantageous for CFST arch bridges, as the arch rib provides a continuous load path that maintains structural integrity even under partial cable failure.

Span Length Influence

The parametric study across 11 different span lengths reveals that dynamic coefficients remain relatively constant across the span range studied. This consistency simplifies design practice by allowing engineers to apply uniform dynamic coefficients without span-specific calibration, provided the bridge configuration falls within the studied range.

Engineering Practice Integration

The equivalent static calculation method presented in this research offers a practical and efficient approach for assessing the structural response of CFST arch bridges to hanger rupture. Compared to full dynamic time-history analysis, the equivalent static method significantly reduces computational complexity while maintaining acceptable accuracy for design purposes. This makes it particularly suitable for:

1. Preliminary design assessment: Rapid evaluation of structural robustness during the conceptual design phase.
2. Code compliance checking: Verification of redundancy and robustness requirements in bridge design codes.
3. Existing bridge evaluation: Assessment of in-service bridge performance under potential hanger rupture scenarios.
4. Mitigation measure design: Optimization of structural modifications to improve hanger rupture resistance.

The electromagnetic rupture trigger device developed in this study represents a significant advancement in experimental methodology for bridge robustness testing. The ability to achieve controlled instantaneous rupture within 0.1 seconds enables accurate simulation of the dynamic effects that are difficult to capture through quasi-static testing methods.

Study Insights and Implications

This research makes a substantial contribution to the structural safety assessment of CFST arch bridges by providing validated dynamic coefficients for equivalent static analysis of hanger rupture scenarios. The experimental validation through large-scale testing combined with finite element simulation provides high confidence in the proposed method's accuracy and applicability. Engineers should note that the proposed dynamic coefficients are derived from specific bridge configurations and loading conditions, and extrapolation beyond the studied parameter ranges should be performed with caution. Future work should extend to considering multiple simultaneous hanger ruptures, progressive collapse scenarios, and the influence of different hanger material properties on dynamic response characteristics. The developed methodology and dynamic coefficients provide a valuable foundation for incorporating hanger rupture robustness requirements into bridge design codes and standards.