SEISMIC PERFORMANCE OF SLIDING ISOLATION BEARINGS DURING VERTICAL MOVEMENT OF BRIDGE GIRDERS

The behavior of sliding isolation bearings with respect to vertical movement due to earthquake excitation is investigated through experiments and simulations. Bridge girders may undergo vertical motion during severe earthquake events, and since the friction damping provided by sliding isolation bearings is dependent on maintaining contact between the bearing and the girder, there remains an issue as to whether sliding isolation bearings are appropriate for this application. It was shown in this study that multi-layer rubber horizontal load distribution (HLD) devices with steel plate reinforcement are essential for bridge applications, as non-reinforced HLD devices are likely to fail under severe vertical tensile loads. The bearing surface, however, is found to be resilient to impact with an uplifted girder, and simulations demonstrate that contact is maintained with at least one bearing during severe ground motion due to lateral rocking of the girder. The results therefore suggest that appropriately designed sliding isolation bearings are suitable for bridge applications.