Failures of US bridge rocker bearings

Bridge bearings made of iron or steel, first used in early railroad bridges about 150 years ago, are relatively small structural components that support the loads of bridge superstructures. Fixed bearings directly transfer forces from a bridges superstructure to its substructure. Movable bearings, such as sliding bearing plates, rollers and rockers, accommodate the thermal expansion of the superstructure without transferring it to the substructure. Rocker bearings tilt to accommodate thermal movement, theoretically without imposing stresses on the substructure. This paper concerns rocker bearings which are non-redundant components and have two states: stable and toppled over. When these bearings topple over, no alternate load paths exist, which results in a failed superstructure. As such, rocker bearings are critical bridge components. An overview is given of the history of use and failures of rocker bearings from nineteenth-century railroad bridges to US highway bridges with tall and slender rocker bearings that date from the late 1950s.