Stability analysis of a three-span continuous single-rib steel box tied-arch bridge

This study investigates the stability performance of a single arch ribbed steel box tied arch bridge using the Zhengzhou Xincaihong Bridge as a case study. A comprehensive analysis is conducted employing both ANSYS beam element modeling and multi-scale plate-beam modeling of instability-prone regions. The elastic stability analysis reveals that the structure exhibits relatively low lateral bending stiffness, with the first five instability modes all manifesting as out-of-plane buckling of the arch ribs. While geometric nonlinearity demonstrates minimal influence on structural stability, material nonlinearity emerges as the predominant governing factor. Under combined dead load and full live load conditions, the most critical instability position occurs at L/5 (L refers to the span of the side span) of the side arch rib. Parametric studies identify the bending stiffness of side span arch ribs and the rise-span ratio as the most significant factors affecting overall stability. Comparative analysis between modeling approaches shows that multi-scale models predict lower live load ratios than conventional beam elements, with reductions of 2.21% at the mid-span segment and 13.09% at the L/5 section, demonstrating that simplified beam models are not conservative and overestimates structural capacity by neglecting local instability effects. The research further quantifies the impact of key design parameters: structural stability improves with increasing diaphragm quantity (1-3), longitudinal stiffener plate thickness (12-18 mm), and number of top plate stiffeners (2-5 per side), as evidenced by corresponding increases in live load ratio coefficients.