EFFECT OF SEISMIC GROUND MOTION SPATIAL VARIABILITY AND DIRECTIONALITY ON THE NONLINEAR RESPONSE OF A CURVED BRIDGE

Abstract eng:
The spatial and directional characteristics of the seismic excitation may drastically affect the response of extensive or long structures, as well as structures located at irregular sites. For bridges, the incorporation of the spatial and directionality effects in their seismic assessment/retrofit/design depends on: (i) the kinematic and dynamic properties of the structure; (ii) its performance level; (iii) the site conditions, and (iv) the site seismicity. Most of bridge design codes address the effect of the spatial variability and directionality, but their contribution is partially taken into account in the definition of the seismic action. Design codes, such as AASHTO, Caltrans, JRA, mostly deal with the problem of the spatial variability of ground motions on the basis of increasing the seating length. Eurocode 8-Part 2 is the only code that proposes a detailed framework for incorporating the effect of the spatial variability of ground motions in the seismic assessment/design of bridges, presenting both a simplified and an analytical approach. Regarding the directionality effect, there is no method to pre-establish the critical orientation of the seismic waves in order to maximize the seismic forces in all structural components/elements of a specific structure. Therefore, design codes recommend that bridges should be designed to resist seismic forces acting in any possible direction. In the present study, the nonlinear dynamic response of the Mogollon Rim Viaduct, which is a tall, long-span, curved, reinforcedconcrete bridge, is investigated. The effect of the multi-support and multi-directional excitations of ground motions on the design and structural response are investigated, and their appropriate consideration in structural analysis of bridges is discussed. It is noted that the soil-structure interaction is an important factor in inducing pseudo-static forces in the bridge structure, and its appropriate simulation is essential for the safe design of bridges vulnerable to non-uniform excitations. In addition, the study illustrates how the sensitivity of the bridge response to the incident angle of seismic waves can influence the reliability of the analytical fragility curves derived from the conventional incremental dynamic analyses.

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