BRIDGE BEARINGS AND STABILITY

The designers of bridges must assure themselves that bridge bearings can transmit the high horizontal loads of current designs. The proportion of horizontal to vertical load is increasing due to the current trend toward continuous, joint-free, redundant structures. From the 10-20% level of some years ago, horizontal forces are now found at and above the corresponding vertical loads. These horizontal forces require that bearing stability be investigated. Two levels of stability criteria, for normal conditions and for extraordinary temporary conditions, are presented. An overturning factor of safety of 3.0 for rectangular surfaces (5.0 for circular surfaces) is proposed under normal (i.e., dead, wind, and live) loads, while a factor of 1.5 for rectangular surfaces (2.0 for circular surfaces) is proposed under extraordinary (i.e., seismic or construction) temporary loads. Examples of pot, disc, and spherical bearing stability checks are presented.