Development of recommended resistance factors for drilled shafts in weak rocks based on o-cell tests.

Details

• Creators:
  Yang, Xiaoming ; Han, Jie ; Parsons, Robert L.
• Corporate Creators:
  University of Kansas. Dept. of Civil, Environmental and Architectural Engineering
• Subject/TRT Terms:
  • Bridge design
  • Design load
  • Load factor
  • Geotechnical engineering
  • Calibration
  • Weak rock
  • Field tests
  • Resistance (Mechanics)
• Publication/ Report Number:
  K-TRAN: KU-07-4
• Resource Type:
  Tech Report
• Geographical Coverage:
  Kansas
• Corporate Publisher:
  Kansas. Dept. of Transportation. Bureau of Materials & Research
• Abstract:
  From October 1, 2007, the new bridges on federal-aid funded projects are mandated to be designed to meet ; American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design ; (LRFD) Bridge Design Specifications. LRFD is a simplified form of reliability-based design. By multiplying calibrated ; factors to load and resistance components, the designed structure will maintain a specific level of reliability (or ; probability of failure). By concept, the load and resistance factors should be calibrated by large number of test data; ; however, they are often unavailable in geotechnical engineering. Significant efforts are needed to calibrate load and ; resistance factors based on test data of good quality. In this study, 26 O-Cell test data were collected from Kansas, ; Colorado, Missouri, Ohio, and Illinois. Seven methods available in the literature were selected to estimate the load ; capacities of 25 out of 26 drilled shafts. The “FHWA 0.05D” method was found to yield the closest and conservative ; predictions of the nominal resistances to the representative values; therefore, it was adopted in this study when ; calibrating the resistance factors for Strength Limit State design. These test data were analyzed and used to calibrate ; side and base resistance factors for drilled shafts in weak rock. ; Resistance factors were calibrated at two different target reliability indices: 2.3 (i.e., failure probability, Pf≈1/100) ; for shafts with greater redundancy and 3.0 (Pf ≈ 1/1000) for shafts with less redundancy. Side resistance factors were ; calibrated from two different datasets of measured resistance: total side resistance and layered unit side resistance. ; The resistance factors calibrated from layered unit side resistance are considered more reliable, therefore, they are ; recommended for design. The recommended resistance factors from this study are compared with those in AASHTO ; specifications. Some of those calibrated resistance factors from this study are considerably lower than those in ; AASHTO specifications. The main reasons for such lower resistance factors are mainly attributed to the low efficiency ; of the FHWA design method and the limited quality and number of O-Cell test data. These resistance factors may ; be improved by increasing the size and the quality of the test data in the future. At present, field load tests on drilled ; shafts are recommended as an alternative to using lower resistance factors, which will also accumulate more test ; data for future improvement.
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• Format:
  PDF
• Funding:
  C1616
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/27783/dot_27783_DS1.pdf
• File Type:
  [PDF - 972.65 KB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:3073f78a8f56f12d555981063929ac64335310161063df79885ac43d980561ad