Abutments are bridge-supporting structures at the interface of the bridge deck and the soil embankment. During strong seismic events, longitudinal motion of the bridge causes a collision between the deck and the abutment backwall---which is lightly reinforced and is designed to break---and plastic deformations are induced in the backfill. This mechanism is intended to dissipate energy, and concentrate or limit the seismic damage to the abutments (Caltrans SDC, 2010). Reversals of inertial forces can cause the deck to unseat from the abutment, and thus, sufficient seat length is required. Seat type abutments also feature exterior shear keys that are used to counter possible transverse deck movements. They are proportioned and detailed to act as fuses that will break off under the design earthquake (Kaviani et al., 2014).
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