ANIDIS - L'ingegneria Sismica in Italia, ANIDIS XIX & ASSISi XVII - 2022

Dimensione del carattere:  Piccola  Media  Grande

Seismic Performance of Isolated Bridges under Extreme Shaking

Gilberto Mosqueda

Ultima modifica: 2022-08-10


Seismic isolation is a proven strategy for protecting critical infrastructures, such as hospitals, data centers, emergency response facilities, and important bridges, from the damaging effects of the design-level earthquake ground shaking. Seismically isolated highway bridges are expected to provide limited service under a safety evaluation-level ground shaking with minimal to moderate damage. The behavior under extreme shaking, corresponding to a large return period earthquake, could induce unexpected damage, impacting servicibility. In these rare events, the seismic isolation system can be subjected to displacement demands beyond its design capacity resulting in failure of the bearings or exceeding the clearance and pounding against the abutment backwalls. The calculation of the isolation system design displacement capacity is critical for evaluating the safety margin against failure and should be examined, especially considering findindgs from recent studies that indicate isolated buildings designed to current code standards demonstrate an unacceptable risk of collapse for Maximum Considered Earthquake (MCE) shaking. In this study, the seismic performance of a prototype highway bridge considering state-of-the-art models for the bearings and abutment pounding is subjected to a set of ground motions scaled to  and beyond design considerations. This study aims to confidently estimate the bridge lateral displacement, and the transfer of forces to the substructure to assess potential damage modes. Recen models of Lead Rubber Bearings are considered that account for heating of the lead and rubber hardening at large strains. Mitigation strategies to reduce the lateral displacement are studied, targeting the avoidance of damage to critical components such as by the use of dampers at the isolation interface or by designing the bearing to engage a stiffening regime at large displacements.

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