Two uncertainties in simulating spatially varying seismic ground motions: incoherency coefficient and apparent propagation velocity

The main focus of this paper is on uncertainties associated with the selection of the incoherency coefficient and apparent propagation velocity in the simulation of asynchronous seismic excitations based on the provisions of CEN Comité Européen de Normalisation] (Eurocode 8: Design of structures for earthquake resistance—part 2: bridges, BS EN 1998-2:2005, Brussels, Belgium 2005). To this effect, the importance of utilizing appropriate values of these two parameters in the simulation of spatially varying seismic excitations is highlighted, and practice-oriented recommendations are provided for their selection. In addition, preliminary probability distributions are proposed for the consideration of the effect of uncertainty in the selection of the apparent propagation velocity for reliability (fragility) analyses. The effect of multi-support input motions on the seismic response of bridges is also discussed.