Generalized Fragility Curves for Bearing-Supported Skew Bridges, for Arbitrary Angle of Incidence of the Seismic Action

Abstract eng:
In a previous work by the authors and their co-workers an analytical methodology for the derivation of seismic fragility curves for bridges was proposed. Bridges were classified into three main categories according to their seismic energy dissipation mechanism: bridges with yielding piers of the column type, bridges with bearings and non-yielding piers of the wall type, and bridges with bearings and yielding piers of the column type. Then, damage states were defined using deck displacement at characteristic points of ‘typical’ bridge pushover curves, which are related to the seismic energy dissipation mechanism, consistently with the proposed classification scheme. Only one horizontal component of the seismic action was considered to act along the principal directions of the bridge. This methodology was subsequently extended by the authors to take into account the angle of incidence of the seismic action, considering only the single-component case. In the present work the methodology is further extended to the general case wherein the minor principal horizontal component of the earthquake is also taken into account (dual-component seismic action). Furthermore, damage states for bridges with bearings are redefined in a broader manner, to take into account biaxial shear effects, and all possible failure mechanisms of the bearings. The methodology is applied here to a skew bridge, subjected to either single- or dual-component seismic action. The main difference between straight and skew bridges is that the modal principal bridge directions are rotated with respect to the geometric principal bridge directions, for a specific angle of incidence. The proposed methodology is formulated in terms of modal principal directions. The CQC rule is used for the combination of the projections of the control point displacement and of the base shear in the single-component case, while in the dual-component case the SRSS rule is used and it is found adequate for all excitation angles. From the derived generalized fragility curves it is concluded that when the minor principal horizontal component of the earthquake is taken into account, bridge fragility is significantly increased, while it remains practically unaffected by the angle of incidence.

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