Calibration of the live load factor in LRFD design guidelines : [revised].
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Calibration of the live load factor in LRFD design guidelines : [revised].

Filetype[PDF-2.04 MB]


English
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  • Creators:
  • Corporate Creators:
  • Subject/TRT Terms:
  • Publication/ Report Number:
    OR 11 - 003
  • Resource Type:
    Tech Report
  • Geographical Coverage:
    Missouri
  • Edition:
    Final report.
  • Corporate Publisher:
    Missouri. Dept. of Transportation. Organizational Results
  • 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 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 slightly lower than 3.5

    mainly due to the adopted projection method to predict 75 year load. For many bridges in rural areas with Average Daily Truck

    Traffic (ADTT) of 1,000 or less, the average reliability indices are higher than the average reliability index of bridges with ADTT

    of 5,000. 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.

  • Format:
    PDF
  • Funding:
    TRyy0913
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