The National Academies

NCHRP 12-110 [Final]

Proposed New AASHTO Load Rating Provisions for Implements of Husbandry

  Project Data
Funds: $566,864
Research Agency: E&T Consulting Engineers
Principal Investigator: Dr. Gongkang Fu
Effective Date: 10/21/2016
Completion Date: 10/20/2019

NCHRP Research Report 951: AASHTO Load Rating Provisions for Implements of Husbandry presents bridge load rating procedures for implements of husbandry (IoH). The procedures are presented as a proposed AASHTO manual, a set of protocols, and examples of bridge load ratings for IoH. Comprehensive weigh-in-motion data collection and analysis were performed to develop the recommended live load factors.  Various bridge spans and vehicle configurations were analyzed in order to develop the new live load distribution factors. This report will be of immediate interest to bridge engineers responsible for bridge rating and ensuring public safety while allowing IoH to safely cross bridges.

The size, geometry, and weight of farm equipment known as implements of husbandry (IoH) have increased and changed significantly to meet the needs of the modern agricultural industry. While intended primarily for use on the farm or in the field, IoH frequently travel on roads and bridges. A review of the history of bridge design vehicles, and the evolution of truck size and weight legislation clearly show that the growth of IoH has exceeded legal vehicles.  Bridges are designed based on the AASHTO live loads that are different from IoH. Therefore, research was needed to provide guidance to help bridge owners and engineers load rate bridges for IoH in order to both ensure public safety and preserve bridges.


Research was performed under NCHRP Project 12-110 by E&T Consulting Engineers to (1) propose new implements of husbandry (IoH) load rating provisions for the AASHTO Manual for Bridge Evaluation (load factor rating “LFR” and load and resistance factor rating “LRFR”) and related revisions to the AASHTO LRFD Bridge Design Specifications; and (2) develop a set of protocols to evaluate IoH with various configurations for load rating and overload permits.

Appendix B: Proposed AASHTO Guide Manual for Bridge Evaluation for Implements of Husbandry of NCHRP Research Report 951 is available to download at:


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