Investigating Importance of Friction between Elastomer Bearing and Its Support on the Seismic Performance of Skew Seat-type Bridges

Seat-type bridges compose a large portion of bridge inventories in different countries. There is evidence of excellent performance of these bridges in Iran during past earthquakes, that could be attributed to the slip of elastomeric bearings. This study investigates how the coefficient of friction between elastomeric bearing and its support and skew angle of the bridge could affect the performance of seat-type bridges. This assessment is done using incremental dynamic analyses on a three-span model bridge. The finite element model accounts for the slip of bearings, backfill passive resistance, and plastic deformation of columns. The results show that while the skew angle predominantly affects the required seat width in different codes, the correlation between the required seat width and coefficient of friction is much stronger. It is also established that, considering the mean response, there is no possibility of unseating even for maximum considered level ground motion. At the same time, the possibility of a loss of access due to abutment displacement is quite probable even for a design-basis earthquake. Furthermore, it is shown that the slip of the bearings significantly reduces seismic demand on the substructure. The findings show the paramount importance of modeling bearing slip in any seismic assessment of these bridge types