Seismic Research

Editorial by Cliff Freyermuth, Manager, ASBI

This edition of the newsletter includes a report on Phase II of the seismic research project on precast segmental bridges at the University of California San Diego (UCSD). The research project was initiated by ASBI and funded by Caltrans. The project was developed to study the seismic performance of segment-to-segment joints of superstructures with different levels of internal to external post-tensioning, as well as the behavior of segment joints incorporating the specific reinforcement details of the proposed San Francisco-Oakland East Bay Bridge.

The research has demonstrated that precast segmental concrete bridges have the capability of sustaining very high levels of seismic loading, regardless of ratios of internal to external tendons. However, a vitally important finding of this research is that ductility and displacement capacity of segmental concrete bridges can be significantly increased with 100 percent external tendons. This alternative is not presently allowed under AASHTO specifications. On the other hand, the least desirable behavior exhibited was by the specimen with 50 percent internal tendons and 50 percent external tendons, which is currently permitted by AASHTO specifications. After completion of the Phase III tests of superstructure-pier interaction later this year, the ASBI Seismic Committee will develop proposed revisions of AASHTO seismic design provisions to reflect these very important research results.

This research has again demonstrated the indispensable role of physical testing in resolving differences of opinion on complex technical issues. The American Segmental Bridge Institute and the entire bridge engineering community are indebted to Caltrans for funding this research, and to Frieder Seible and his assistants at the UCSD for conceiving and executing the tests in an exemplary manner.