Structural robustness assessment of single cable-plane tied arch bridges: lessons from cable-loss-induced progressive collapse of the Nanfang’ao Bridge in Taiwan

In comparison to the double cable-plane arch bridges, the single cable-plane tied arch bridge is notably susceptible to progressive collapse due to the vulnerability and failure of its unique unilateral cable system during service, highlighting its insufficient structural robustness. The Nanfang’ao Bridge, a collapsed structure located on the seashore of Taiwan, China, featuring a single cable-plane tension-tied arch, was selected as an analytical model for the cable-loss-induced progressive collapse study. A novel robustness assessment methodology, utilising a cable loss block, is proposed for the structural assessment of tension-tied-arch steel bridges after a sudden cable breakage event. The progressive collapse analysis suggests that the single-cable-plane configuration results in inadequate robustness of the weak arch-strong deck bridge, subsequently leading to complete collapse following the fracture of cables due to corrosion. Furthermore, a parametric study on robustness, considering traffic loads, cable pretension, area, and corrosion, reveals that the shortest cables at the bridge ends are critical for robustness, and increasing the cable area improves the structural robustness of the single-arch bridges. Failure risk can be mitigated both by increasing the design bearing capacity of the structural components and by conducting more frequent inspection and maintenance actions.