In recent years many highway overcrossings have been severely damaged by ground shakings of high intensity. Most of the observed damages, such as deck pounding and bearing unseating, are the results of undervalued seismic displacements and deflections. Such deficiencies are the results of dated design approaches which neglect, or wrongly account for, the deformability of the soil-foundation-pier system and of the abutment-embankment system. In particular, the interaction arising between the abutment and the embankment may sensibly affect the seismic response of bridges which are transversally or longitudinally anchored to the abutments and should be taken into account in the analyses.
Some works are available in the literature dealing with the behaviour of bridge embankments; the simplest methods are based on the so-called Shear-Wedge model that considers a unit-length embankment section and accounts for the actual longitudinal dimension by introducing an effective length. The most accurate methods are based on solid finite element models that are characterized by a huge number of dof and require long calculation times.
A new model for the dynamic analysis of embankments is presented in this paper. The higher order formulation proposed permits reducing the 3D problem into a 2D problem obtaining straightforwardly the dynamic impedances and the kinematic response of the system. Applications to abutment-embankment systems with different geometry and soil mechanical properties are reported to demonstrate the importance of including the embankment deformability in the evaluation of the abutment impedances and the bridge input motion.