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1 Background and Report Organization Commercial vehicles represent a major load to roadway bridges. These vehiclesâ weights and weight distributions, as well as their volumes, are critical to bridge safety. Farm equipment (in the form of self-propelled vehicles and their hauled wheeled tools and machines) is generally referred to as âimplements of husbandryâ (IoH). IoH have been considered to be local vehicles on farms that do not use public roads often, if at all. As a result, state and local jurisdictions vary widely in managing IoH. Apparently, the growth of IoH has far outpaced that of other legal highway vehicles, warranting concern with bridge safety. For example, IoH vehicle operators have requested permits to access public roads with axle loads above 60 kips or above 300% of current federal axle weight limit. Roadway bridges in the United States are currently designed based on AASHTO live load models that are different from IoH. Load rating of bridges also uses vehicles more commonly traveling on public roads, rather than typical IoH. Furthermore, IoH causing bridge collapse has also been reported. Those bridges carrying local roads are especially vulnerable because more are load rated low or load posted. Figure 1-1 shows a county bridge collapse in Illinois caused by a farm vehicle. The carried grain was spilled at the site. It appears to be the right time to address IoH as possible loads to roadway bridges, particularly for their load rating. To ensure public safety and preserve bridges, NCHRP Project 12-110 addressed the need to help bridge owners and engineers load rate bridges for IoH. The objectives of this research project were to (1) propose new IoH load-rating provi- sions for the AASHTO Manual for Bridge Evaluation (MBE) in load factor rating (LFR) and load and resistance factor rating (LRFR), along with related revisions to the AASHTO LRFD Bridge Design Specifications (BDS); and to (2) develop protocols to evaluate IoH with various configurations for load rating and overload permits. This report documents the research process and products. NCHRP Research Report 951 consists of four chapters. Besides this chapter, Chapter 2 presents the phased tasks of this research project, along with progress management. Chapter 3 summarizes the major findings of this research effort. Besides those from a nationwide survey on the practice of IoH management and related concerns, other technical subjects are addressed. They include 1. Modeling of IoH vehicle loads, 2. Lateral live load distribution of IoH loads mainly because of their different gauge widths from the typical 6 ft, 3. Dynamic impact of IoH vehicles, and 4. Live load factor for load rating and permit review for IoH vehicle loads. C H A P T E R 1
2 Proposed AASHTO Load Rating Provisions for Implements of Husbandry Current states of the art and the practice relevant to these technical subjects are also provided in Chapter 3 as a starting point of research. This research effort was designed to advance these states of the art and the practice to meet the needs of bridge owners and economic development. Chapter 4 summarizes the major conclusions of this research project. It also suggests further research relevant to IoH load rating and permit review. Figure 1-1. Bridge collapse in Illinois caused by a farm vehicle in 2011.