Vulnerability assessment of single-pylon cable-stayed bridges using plastic limit analysis

Vulnerability of a structure hazards can be regarded as the study of its strength and robustness against damages caused by these hazards. Measures to quantify vulnerability of a structure provide an insight into its possible performance and help to identify critical components or damage locations that can lead to a catastrophic consequence. From structural viewpoint, one possible quantitative measure for structural vulnerability assessment is the ultimate load-carrying capacity. In this study, a technique based on the plastic limit analysis is proposed for the vulnerability assessment of single-pylon cable-stayed bridges. The limit analysis assumes that, for a steady-state collapse without an inertia effect, the power done by the external forces is dissipated by the yielding components. Hence the ultimate load-carrying capacity of a bridge can be calculated directly if a proper collapse pattern is assumed. Such a concept is illustrated by assuming plastic hinge models for the healthy and the damaged bridge. The technique is illustrated on a single-pylon cable-stayed bridge with two equal side spans of 200 m. Results show that the load-carrying capacities of both the healthy and the damaged bridges can be accurately determined using this technique. The proposed technique not only provides an efficient tool to assess the vulnerability of a single-pylon cable-stayed bridge but also can be used to study the effects of different design parameters on the load-carrying capacity and the vulnerability of cable-stayed bridges.