Earthquake Retrofit of California Bridge Route 242/680 Separation


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Title: Earthquake Retrofit of California Bridge Route 242/680 Separation

Author(s): R. C. Fish and G. L. Rowe

Publication: Special Publication

Volume: 187


Appears on pages(s): 361-374

Keywords: bearings; bridges; isolation; retrofit; seismic.

Date: 6/1/1999

The bridge investigated consists of two very different structure types joined by a voided pier at Bent 4 that serves as a central abutment for both. The final retrofit design strategy used some "standard" Caltrans retrofit techniques and incorporated some innovative and unique design elements. It is the unique elements of the " South" structure's retrofit that is the focus of this paper. The bearings at Abutment 1 and Bents 4 were replaced with Dynamic Isolation Bearings. The fixed bearing at Bents 2 and 3 were replaced with low friction Spherical Expansion Bearings. This system "Highly" isolate the superstructure from the Bents 2 and 3 eliminating a costly foundation retrofit. Additional structural modifications included four buttress walls attached to a pile supported grade beam at Bent 4 and modification to the bearing pedestals at Abutment 1. These served to resist the Forces transferred from the Dynamic Isolation Bearings. Also, steel frame to act as a seat extension for the slab spans and concrete blocks to prevent crushing of the slabs was installed. Construction was completed in 1995. The innovative techniques used in the seismic retrofit of this bridge, resulted in savings compared to a more costly conventional retrofit. It significantly reduces impact during construction to the high volume of traffic on both Route 242 and Route680 and will reduce the susceptibility to damage during an earthquake as compared to a conventional column strengthening retrofit.