The National Academies

NCHRP 20-07/Task 285 [Final]

Recalibration of the LRFR Load Factors in the AASHTO Manual for Bridge Evaluation
[ NCHRP 20-07 (Research for AASHTO Standing Committee on Highways) ]

  Project Data
Funds: $100,000
Research Agency: HNTB Corporation
Principal Investigator: Bala Sivakumar
Effective Date: 3/4/2010
Completion Date: 5/27/2011

The object of this study is to use recent national weight-in-motion (WIM) data to recalibrate the Load and Resistance Factor Rating (LRFR) live load factors for permit load ratings given in the AASHTO Manual for Bridge Evaluation and to adjust these live load factors based on the method of analysis used during the load rating process. This study has also taken into consideration current WIM data to verify that the AASHTO LRFR produce acceptable and uniform levels of reliability for typical U.S. bridges under current loading conditions. The target reliability index set for the permit load recalibration is βtarget=2.5 with the goal of achieving reliability index values for all conditions that remain above a minimum βmin=1.50 . A minimum live load factor of 1.10 was also maintained for all permit ratings. The protocols established in NCHRP Report 683 were adapted to the application here of bridge rating recalibration. This report presents the results of the reliability calibration of the permit live load factors for use in proposed revisions to the AASHTO LRFR. Permit load factors are provided for routine permits and special or trip permits for use with the AASHTO LRFD distribution factors and with refined methods of distribution analysis. These new load factors will result in improved permit load ratings in most cases when used in conjunction with the LRFR methodology.

Products Availability: Agency final report was submitted to AASHTO Technical Committee on Bridge Management, Evaluation, and Rehabilitation (T-18). (NCHRP Staff: W. Dekelbab)

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