Abstract
This paper investigates the quantitative effects of ground motion directionality on fragility curves of highway bridges. For this purpose, the influence of soil-structure interaction (SSI) is also included in finite-element modeling, and models of reinforced concrete bridges are generated assuming five different skew angles to account for geometric irregularity. A set of horizontal pairs of ground motions is imposed to the bridge models through nonlinear dynamic analyses. Twelve various angles of seismic incidence, ranging from 0° to 180°, are considered to account for ground motion directionality. Probabilistic seismic demand models are constructed for four structural components (i.e., column, deck at abutment seat, shear key, and elastomeric bearing), and fragility curves are developed. Additionally, the spatial distribution of column demand is investigated using a method giving the maximum resultant of column responses along the bridge horizontal axes. The results show that the most critical angle of seismic excitations does not necessarily coincide the orthogonal axes of the bridge. Response sensitivity of the bridge components to ground motion directionality effects varies from 30% to 50%. Furthermore, when the spatial distribution of column demand is considered, the results are up to 20% more conservative than those obtained along the bridge principal axes only. Fragility results also indicate that the response sensitivity of components to variation in the angle of seismic incidence and the response sensitivity of columns to the method of obtaining curvature ductility demand are more pronounced in SSI models compared to those in fixed-base models.
Published Version
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