Bridge Bearings - Caltrans

M e mo t o D e s ig n e r s 7-1 * J u n e 1994. Bridge Bearings Introduction AASHTO defines a bearing as a structural device that transmits loads while facilitating translation and/or rotation . 1 In the past Caltrans has used a variety of Bearings with varying degrees of success. These include rockers, rollers, pins, pots, steel girder hangers, PTFE/elastomeric, and elastomeric pads. Of all the Bearings mentioned, the reinforced elastomeric bearing (introduced in 1955) has been the most widely used the past four decades. As design trends have shifted toward designs that favor structures with longer frames and fewer joints for seismic reasons, not to mention the widespread use of curved and skewed bridges, the demands on Bearings have increased. Provisions must be made for large longitudinal displacements due to temperature, prestress shortening, shrink- age, creep and seismic activities, as well as rotations produced by changes in camber, live load, and misalignment of bearing seats due to construction tolerances.

The minimum shape factor (5) for any reinforced bearing shall be 5.0. Unless shear deformation is prevented, the average compressive stress, 5C, in any layer of any reinforced bearing with an . S > 5.0 shall not exceed 800 psi. The minimum average compressive stress due to dead load will not be less than 200 psi. The Transportation

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