SEISMIC RETROFIT OF SOUTHERN FREEWAY VIADUCT, ROUTE 280 (SINGLE-LEVEL SEGMENT), SAN FRANCISCO, CALIFORNIA

The Loma Prieta earthquake of 1989 generated the need to strengthen the single-level Southern Freeway Viaduct. The double-deck portion just south of this project was damaged, and the whole viaduct was closed to traffic. The Southern Freeway Viaduct is a continuous reinforced concrete box girder bridge built in 1964 in accordance with the AASHO (now AASHTO) standard specifications. The viaduct is composed of three main lines, as follows: ES Line, SE/A Line, and R1 Line. The columns are rectangular with inadequate tied reinforcement. The columns at most multicolumn bents are pinned at the bottom. Several of the fixed-base columns have lap splices. The majority of footings are supported on steel HP piles; however, some are spread footings. The footings do not have top mat and shear reinforcing. Several of the A-Line bents north of 25th Street are outriggers. Soil conditions at the southern section (south of Bent 73 on the main lines) can be classified as soft bay mud sites, whereas more generally, the site has a combination of a thick soft bay mud layer and a large depth to bedrock. The northern segment is founded on bedrock or stiff soils. Most of the deficiencies found in the viaduct are related to the original design of the hinges, columns, footings, and outriggers. Solutions to retrofitting the viaduct were limited by the existing conditions and existing features (i.e., railroad lines, streets, leased airspace below the viaduct, utilities, etc.) within the project limits. The retrofit strengthening concepts used on the project included the following: hinge retrofits, separation of two level bents, steel column casings, column strengthenings (additional vertical steel encased within a steel casing), grade beam retrofit, new drop caps (bent replacements), elimination or retrofit of outriggers, and footing retrofits. This final retrofit strategy met the required seismic performance goals established by the California Department of Transportation for this project to prevent collapse and provide serviceability after a maximum credible earthquake.

Language

  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 88-100
  • Monograph Title: FOURTH INTERNATIONAL BRIDGE ENGINEERING CONFERENCE, SAN FRANCISCO, CALIFORNIA, AUGUST 28-30, 1995. CONFERENCE PROCEEDINGS, 2 VOLUMES
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00711714
  • Record Type: Publication
  • ISBN: 0309061091
  • Files: TRIS, TRB
  • Created Date: Sep 6 1995 12:00AM