SEISMIC PROTECTION OF BRIDGES

During the past 2 decades, bridge engineers have gained a better understanding of the behavior of structures during an earthquake. The ductility-design philosophy is the mainframe of modern seismic-design guidelines in the United States and most countries abroad. While this design philosophy provides safety against collapse, it tends to be costly because of the damage induced in plastic-hinge zones and to the severe lateral displacements that can occur even in a moderate earthquake. Therefore, in recent years, design engineers have sought an alternative design philosophy that avoids or limits damage to a bridge to maintain postearthquake serviceability. Seismic isolation has emerged as one of the most promising retrofitting strategies for improving the seismic performance of existing bridges. It is also an attractive approach for new construction when conventional design is not suitable or economical. In January 1994, the Federal Highway Administration, California Department of Transportation, and the Highway Innovative Technology Evaluation Center cooperated in launching a full-scale, dynamic testing and evaluation program of readily available seismic isolation and energy dissipation systems. A total of 11 domestic and international manufacturers completed the testing program. The program is expected to increase the confidence level of bridge owners and lead them to consider and use isolation/damping technology cost-effectively to protect otherwise vulnerable structures from more severe earthquake damage. In addition, it will provide useful data to academic researchers.