Longitudinal Restraint Response of Existing Bridge Bearings

Fifteen rocker bridge bearings were cyclically tested to determine their bearing response to simulated seismic longitudinal loads. The objective of the tests was to examine the load-deformation characteristics and energy dissipation capabilities of bearings that have been in service for many years. The results are to be used to determine if existing in-place bearings may be utilized in seismic retrofitting of earthquake-susceptible bridges. The bearings were cycled within working ranges in each direction in the as-received state. The desired friction force hysteretic loops were determined from the net horizontal force-deformation test results. The cycles were applied in a sinusoidal manner in deflection control with a 4-s period to simulate dynamic demand on the bearing. An equivalent friction coefficient was calculated for each bearing. Four of the bearings were tested statically to failure to examine the limit state response. The ultimate limit tests produced horizontal load-deformation data. The horizontal force was applied slowly in deflection control while data were acquired until failure. The ultimate bearing tests showed that all four bearings had large deflection capacities before instability.