Assessment of seismic behavior of r.c. bridges under asynchronous motion and comparison with simplified approaches

The seismic motion is characterized by temporal and spatial variability, that become significant in structures with long longitudinal development, such bridges and viaducts. In those cases, the differential displacements of the supports may have adverse effects, either on the piers responses either on the deck deformations. In this paper, asynchronous and synchronous dynamic analyses on continuous-span bridges are carried out using the finite element method. To assess when considering the synchronous action becomes disadvantageous, a parametric analysis, varying the geometry of the bridge and the soil foundation characteristics, is conducted. The bridges are subjected to sets of artificial accelerograms generated on the base of previous study of the authors (Nuti and Vanzi, 2005). The study is part of a research project, funded by Italian Ministry for Research, that deals the response of bridges subjected to asynchronous motion, including local site amplification.