FIELD TESTING OF BRIDGE DESIGN AND RETROFIT CONCEPTS. PART 1 OF 2: FIELD TESTING AND DYNAMIC ANALYSIS OF A FOUR-SPAN SEISMICALLY ISOLATED VIADUCT IN WALNUT CREEK, CALIFORNIA

The opportunity for the field testing of an isolated viaduct arose out of the demolition and reconstruction of the I-680/R-24 interchange in Walnut Creek, California. The southern section of the temporary separator bridge is seismically isolated, and this portion was the subject of a three-phase field study. This viaduct is the first new bridge in California to be seismically isolated. The primary objective of this investigation was to collect field data for the determination of the dynamic properties (mode shapes, modal frequencies, and damping ratios) of the viaduct, to assess the contribution of different structural components to the overall flexibility and damping characteristics of the structure, and to conduct analytical studies to verify the experimentally computed dynamic properties. The field testing schedule was divided into three phases. During Phase I, individual bents of the viaduct were tested. From pull-over and snap-back testing of individual bents, experimental values for the bent frequency, damping ratio, and length to point of fixity were determined. These values compared favorably with the analytical and design values. In Phase II, the steady state response of the viaduct was obtained for a wide frequency range using two vibration generators. The experimental data was used to compute modal properties in the viaduct's three principal directions. Analytical studies provided satisfactory comparison with the computed values. During Phase III, the viaduct deck was pushed longitudinally to about two-thirds of the isolation bearing design deformations, and then suddenly released. The resulting free vibration response was used to compute the viaduct dynamic properties in the nonlinear range. These properties were closely correlated by nonlinear dynamic simulations. Due to amplitude dependance of the viaduct response, the computed vibration frequencies and damping ratios of the viaduct differed from design analysis values. Ambient measurements were also recorded concurrent with the various stages of the field testing. The obtained frequencies were close to other computed values.

• Corporate Authors:

  University of California, Berkeley

  Earthquake Engineering Research Center
  Berkeley, CA  United States  94720

  California Department of Transportation

  1120 N Street
  Sacramento, CA  United States  95814
• Authors:
  • Gilani, A S
  • Mahin, S A
  • Fenves, G L
  • Aiken, I D
  • Chavez, J W
• Publication Date: 1995-12

Language

• English

Media Info

• Features: Appendices; Figures; References; Tables;
• Pagination: 262 p.

Subject/Index Terms

• TRT Terms: Bridge design; Bridge superstructures; Bridges; Dynamic tests; Earthquake engineering; Field tests; Nonlinear systems; Retrofitting; Seismicity; Structural design; Viaducts; Vibration tests
• Uncontrolled Terms: Bridge spans; Dynamic analysis; Forced vibration tests; Seismic investigations
• Geographic Terms: California
• Old TRIS Terms: Four; Snap-back tests
• Subject Areas: Bridges and other structures; Design; Highways; I24: Design of Bridges and Retaining Walls;

Filing Info

• Accession Number: 00737049
• Record Type: Publication
• Report/Paper Numbers: UCB/EERC-95/14,, Final Report
• Contract Numbers: RTA 59A018
• Files: TRIS, STATEDOT
• Created Date: May 26 1997 12:00AM