Passive Force Behavior for Skewed Bridge Abutments During Combined Lateral and Rotational Loading

As part of pooled fund study TPF-5(264), led by the Utah Department of Transportation (UDOT) and supported by the Federal Highway Administration (FHWA) and a few other state departments of transportation (DOTs), large-scale passive force-deflection tests were performed on a simulated bridge abutment to investigate the effect of skew angle on passive force behavior. Tests were conducted at abutment skew angles of 0°, 15°, 30°, and 45° with a backwall that was 11 ft wide and 5.5 ft tall. Backfills included sand and sandy gravel compacted to 95% of the modified Proctor maximum dry unit weight. Test results indicate that the passive force decreases significantly as the abutment skew angle increases to 45° relative to non-skewed walls. The results also indicate that the reduced passive force for a skewed abutment, Pp(skew), can be predicted using a simple reduction factor, Rskew, multiplied by the passive force for a non-skewed abutment with the same roadway width. The skew reduction factor was relatively consistent for all soil types, wingwall styles, and backfill width-to-height ratios investigated. The Phase II part of the previous study included testing of additional backfill materials and an inclined loading (push-and-rotate) condition for a 30° skew angle. No significant effect on the passive force skew reduction factor was observed in the inclined loading testing that involved relatively small rotation. Based on the previous study results, the skew reduction factor has already been implemented in the California Department of Transportation (Caltrans) Seismic Design Criteria, along with geotechnical guidelines for Oregon DOT and UDOT. However, as designers have started applying this approach, several questions have arisen. For example, in most of the field abutment tests, the simulated bridge abutment was forced to move longitudinally into the backfill soil.  In contrast, during earthquake loadings, the abutment has been observed to rotate. Although this rotation angle is quite small, it can lead to a significant difference in longitudinal displacement from the edges of the abutment from rotation. This would be expected to lead to a triangular distribution of pressure on the backwall of the abutment. Designers want to know (1) if the skew reduction factors remain the same when rotation is involved, and (2) if it is necessary to distribute the passive force non-uniformly along the backwall of the abutment. OBJECTIVES: The objective of this new study is to assist with the calibration of numerical models by conducting a series of large-scale skewed abutment, passive force-displacement tests with enough abutment offset from rotation to evaluate the skew reduction factor and backwall pressure distribution. The maximum rotation and displacement would be larger than in the previous testing. As availability allows, the tests would be conducted at the same Salt Lake Airport test site used in the previous study.

• Record URL:
  http://www.pooledfund.org/Details/Study/775

Language

• English

Project

• Status: Programmed
• Funding: $385000
• Contract Numbers:

  TPF-5(542)

• Sponsor Organizations:

  California Department of Transportation

  1227 O Street
  Sacramento, CA  United States  95814

  Idaho Department of Transportation

  P.O. Box 7129
  3311 W. State Street
  Boise, ID  United States  83707-1129

  Utah Department of Transportation

  4501 South 2700 West
  Project Development
  Salt Lake City, UT  United States  84114-8380

  Washington State Department of Transportation

  Transportation Building
  Olympia, WA  United States  98504

  South Carolina Department of Transportation

  955 Park Street
  P.O. Box 191
  Columbia, SC  United States  29202-0191

  New York State Department of Transportation

  50 Wolf Road
  Albany, NY  United States  12232
• Managing Organizations:

  Utah Department of Transportation

  4501 South 2700 West
  Project Development
  Salt Lake City, UT  United States  84114-8380
• Project Managers:

  Stevens, David

• Start Date: 20240912
• Expected Completion Date: 0
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Backfilling; Bridge abutments; Calibration; Deflection tests; Mathematical models; Seismicity; Skewed structures
• Subject Areas: Bridges and other structures; Geotechnology; Highways; Maintenance and Preservation;

Filing Info

• Accession Number: 01930054
• Record Type: Research project
• Source Agency: Federal Highway Administration
• Contract Numbers: TPF-5(542)
• Files: RIP, USDOT, STATEDOT
• Created Date: Sep 12 2024 5:01PM