The National Academies

NCHRP 15-54 [Final]

Proposed Modifications to AASHTO Culvert Load Rating Specifications

  Project Data
Funds: $500,000
Research Agency: Michael Baker, Jr., Inc.
Principal Investigator: Mr. Mark Mlynarski
Effective Date: 7/7/2015
Completion Date: 3/31/2019
Comments: Available as NCHRP Web-only Document 268 in January 2020

The choice of load rating method may affect the transportation of goods and services over the nation’s highways by imposing load limits on routes that were previously unrestricted. For culvert load rating, engineers use the load and resistance factor rating (LRFR), load factor rating (LFR), or allowable stress rating (ASR) of highway bridges according to the AASHTO Manual for Bridge Evaluation. However, culverts respond to live loads differently than bridges as a result of surrounding soils. Moreover, the LRFR is calibrated based primarily on bridge response to gross truck weight, while culvert response should be calibrated based on a single axle or a single wheel. As a result, the current specifications may be either overly conservative or inadequate, which may lead to expensive replacements or upgrades, or premature deterioration or failure, respectively. Therefore, there is an immediate need to develop a load rating process for culvert structures to maintain an acceptable level of culvert reliability without unnecessary restrictions on commerce.
The TRB National Cooperative Highway Research Program's Web-Only Document 268: Proposed Modifications to AASHTO Culvert Load Rating Specifications proposes modifications to the culvert load rating specifications in the Manual for Bridge Evaluation and revises the AASHTO LRFD Bridge Design Specifications accordingly.

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