Calibration of the live load factor in LRFD design guidelines.

Details

• Creators:
  Kwon, Oh-Sung ; Orton, Sarah ; Salim, Hani ; Kim, Eungsoo ; Hazlett, Tim
• Corporate Creators:
  Missouri. Dept. of Transportation. Organizational Results
• Subject/TRT Terms:
  • Load factor
  • Design load
  • Calibration
  • Live loads
  • Guidelines
  • Bridges
  • Load factor design
  • Bridges--Missouri
• Publication/ Report Number:
  OR11-003
• Resource Type:
  Tech Report
• Geographical Coverage:
  Missouri
• Edition:
  Final report.
• Corporate Publisher:
  Missouri. Department of Transportation
• Abstract:
  The Load and Resistant Factor Design (LRFD) approach is based on the concept of structural reliability. The approach is ; more rational than the former design approaches such as Load Factor Design or Allowable Stress Design. The LRFD ; Specification for Bridge Design has been developed through the 1990s and 2000s. In the development process, many factors were ; carefully calibrated such that a structure designed with LRFD can achieve a reliability index of 3.5 for a single bridge girder ; (probability of failure of about 2 in 10,000). As the initial development of the factors in the LRFD Specification was intended to ; be applied to the entire nation, state-specific traffic conditions or bridge configuration were not considered in the development ; process. In addition, due to lack of reliable truck weigh data in the early 1990s in the U.S., the truck weights from Ontario, ; Canada measured in the 1970s were used for the calibration. Hence, the reliability of bridges designed with the current LRFD ; specification needs to be evaluated based on the Missouri-specific data and the load factor needs to be re-calibrated for optimal ; design of bridges. ; The objective of the study presented in this report is to calibrate the live load factor in the Strength I Limit State in the ; AASHTO LRFD Bridge Design Specification. The calibration is based on the Missouri-specific data such as typical bridge ; configurations, traffic volume, and truck weights. The typical bridge configurations and the average daily truck traffic of the ; bridges in Missouri are identified from statistical analyses of 2007 National Bridge Inventory. The Weigh-In-Motion (WIM) data ; from 24 WIM stations in Missouri are used to simulate realistic truck loads. Updated material and geometric parameters are also ; used to update the resistance distributions. ; From this study, it was found that most representative bridges in Missouri have reliability indices higher than 3.5. For ; many bridges in rural areas with Average Daily Truck Traffic (ADTT) of 1,000 or less, the average reliability indices are higher ; than 5.0. This study proposes a table of calibration factors which can be applied to the current live load factor of 1.75. The ; calibration factor is developed as a function of ADTT such that bridge design practitioners can select a calibration factor ; considering the expected ADTTs of a bridge throughout its life span. Impact of the calibration factor on the up-front bridge ; construction cost is also presented.
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• Format:
  PDF
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/18380/dot_18380_DS1.pdf
• File Type:
  [PDF - 1.83 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:ab2f7746b25f7c74a045197246e69f383392d8a040387c9b62437bdae075632c