Seismic response of single-span simply supported and continuous slab-on-girder steel bridges is studied. Linear elastic and nonlinear inelastic analyses are conducted for various ground-acceleration inputs. Bearings with higher stiffnesses that are closer to the edge of the deck are found to attract larger forces than other bearings, whereas bearings with small stiffness attract almost equal forces regardless of the width of the brid e. Assuming that the anchors of otherwise stable bearings are severed, sliding of the bridges is also a investigated. It is found that narrower bridges with longer spans may have considerable sliding displacements and may fall off their supports if adequate seat width is not provided. Wider bridges with shorter spans can survive rather severe earthquakes, even more so in eastern North America. It is found that if bearings are not damaged, 2- and 3-lane continuous bridges with two spans of up to 40 and 50 m each, respectively, are capable to resist earthquakes with 0.4g peak acceleration without any damage to columns. However, bridges with only about 80% of these spans can survive similarly intense earthquakes if the bearings are damaged.