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Over the past few decades, the national industry has seen the number of farms decrease with a simultaneous increase in the average farm size. With larger farms and continuously improving farming techniques, the need to increase production and efficiency has affected equipment carrying capacity and completely changed the tools being used. During select seasons, it is common to have single -axle loads on secondary roads and bridges that exceed normal load limits (typical examples are grain carts and manure wagons). Even though these load levels occur only during a short period of time of the year (fall for grain carts and spring for manure wagons), there is concern that they can do significant damage to pavements and bridges. Currently, the only limitation placed upon farm implements is a metric based upon the load per unit width of tire. This metric does not appear to be consistent with the metrics commonly used during design of infrastructure. The objective of the work presented in this report was to perform a synthesis study related to the impacts of heavy agriculture vehicles on Minnesota pavements and bridges and to identify those impacts. The synthesis and associated analyses were completed using metrics that are consistent with engineering design and evaluation concepts. The conclusion of this study validates the years of close observation of highway and bridge engineers that the heavy agricultural loads can cause potential problems in terms of both safety to the traveling public and added costs to the maintenance of the local system of highway infrastructure.

The primary objective of this work is to provide formal guidance to county engineers throughout Minnesota for repairing timber bridge components. The benefit of having such a resource will be measured by improving the overall condition of the transportation system and reducing system failures through implementation by local officials. As is often the case, funds required to complete repairs are limited and, as a result, any method used must not only be structurally feasible but also economically feasible. This report provides bridge owners and caretakers several routine maintenance and repair options aimed to meet the goals of simplicity and affordability. The economic impact of repairing timber bridges was assessed for multiple scenarios: a comparison was made between the net present value of repair at varying repair costs over time and the net present value of varying reconstruction costs over time. Through this exercise, for each scenario, a point in time was identified when repair or reconstruction makes most economic sense. An additional assessment of overall costs (direct plus indirect) was completed, which included the increased user costs due to bridge posting or closure. This assessment made clear that when indirect costs are included, the benefits of maintaining or repairing a bridge to prevent posting or closure become great. A standalone manual, Cost-Effective Timber Bridge Repairs: Manual for Repairs of Timber Bridges in Minnesota, and a technical summary, Manual gives cost-effective techniques to extend timber bridge life spans, were also developed for this project.

One of the primary objectives of this project, Development of Cost-Effective Timber Bridge Repair Techniques for Minnesota, was to produce a timber bridge repair manual. This manual is comprised of some of the content from the final report for the project, along with an extended presentation of timber maintenance options. This final manual is a standalone document from which the maintenance and repair options can be implemented. A final report (2015-45A, "Development of Cost-effective Timber Bridge Repair Techniques for Minnesota") and a technical summary (Manual Gives Cost-Effective Techniques to Extend Timber Bridge Life Spans) were also developed.

The Minnesota Department of Transportation (MnDOT) constructed its first glass fiber polymer (GFRP) reinforced bridge deck on MN 42 over Dry Creek just north of Elgin; Minnesota. Successful implementation of the GFRP reinforced bridge decks would eliminate the steel corrosion problems that often shorten the life of the deck. Although there has been wide use of GFRP reinforcement in bridge decks in some parts of Canada; there have been relatively few GFRP reinforced bridge decks built in the United States. The Canadian decks were primarily designed using the empirical design method in the Canadian Highway Bridge Design Code. This method differs significantly from thee design guidelines produced by AASHTO and ACI Committee 440 on fiber-reinforced polymer (FRP) reinforcement. To maximize the knowledge and experience gained in constructing this type of bridge decks; this research project investigates the performance of a case-study bridge deck focusing on key issues such as cracking; deck stiffness; load distribution factors; and GFRP rebar strains. The main goals of this project are: • Collect behavior information and response characteristics of the bridge deck under service loads ·Identify the load distribution characteristics; especially for the bridge girders supporting the deck • Examine the short- and long-term durability of the bridge deck in terms of formation and propagation of cracks • Assess the impact of using non-conventional; corrosion-resistant deck reinforcement on maintenance needs and life-cycle cost with a specific interest in including service-life design philosophies. The outcome of this project will directly contribute to the development of guidance and details for the construction of corrosion-resistant bridges with service lives beyond 100 years.

Many state Departments of Transportation (DOT) across the US; including MnDOT; are experiencing problems associated with loose anchor bolts used in support structures (e.g.; overhead signs; high-mast light tower (HMLT); and tall traffic signals). Specifically; MnDOT inspection crews have found loose nuts at most anchor bolt locations; even at some newly installed signs. Many of these nuts became loose in less than two years; even after being tightened by the maintenance crew following current recommended procedures. This situation has placed great strain on the resources from the districts' maintenance group and also causes concerns related to inspection frequency and public safety. This project investigated causes of the loose anchor bolts and proposes solutions based on site surveying; field monitoring; laboratory study; and numerical analysis. The research team found that the tightening process proposed in AASHTO's specification is a sufficient alternative for MnDOT; though it requires modification in three key areas: defining snug-tight; accounting for grip length; and recommending verification procedures. The research team quantified snug-tight values; and defined the relationship between torque; tension; and nut rotation through empirical constants. Recommendations are made for a new specification for MnDOT structures.

Throughout the US; many state departments of transportation (DOTs) are experiencing issues with the loosening of anchor bolt nuts on overhead sign; luminaire; and traffic signal (SLTS) structures. Retightening loose nuts imposes a significant drain on state DOT resources. In addition; loosening of these nuts increases fatigue stresses on the anchor bolts; possibly increasing the risk of failure. Loose anchor bolt nuts were recorded on both old and new structures; some immediately after installation. Even after retightening by Minnesota Department of Transportation (MnDOT) maintenance workers; anchor bolt nuts were found to come loose within two years. In a previous project; new retightening specifications were developed based on laboratory testing; field monitoring; surveys of current practices; and finite element modeling. This project focused on implementation and evaluation of the proposed specifications from the previous project. Structural monitoring also continued on a previously instrumented overhead sign structure. Difficulties were discovered with the proposed procedures during implementation; including structure clearance; instruction clarity; and retightening timing. Overall; though; the proposed procedures were found to be effective in preventing loosening. Revisions to the specifications were suggested along with recommendations for further review to simplify the procedures through a future laboratory study.

The Minnesota Department of Transportation (MnDOT) funded two projects in an effort to mitigate anchor bolt connection loosening and develop improved pre-tensioning steps for its sign, luminaire, and traffic signal (SLTS) structures. The Phase I study proposed new pre-tensioning procedures, completed laboratory testing, did an in-depth literature review, and set up instrumentation. The next part of the work started by implementing the proposed procedures in the field and suggesting revisions to be investigated further in Phase II. Through this work, the structural monitoring objective was to better understand field fatigue forces on the anchor rods and develop a testing procedure to replicate field stresses accurately in the laboratory. In the Phase II project, lessons learned from both the field results and additional literature review were tested in the laboratory to balance the efficiency and efficacy of the revised pre-tensioning procedures. Feedback from stakeholders and experience from in-field inspections were considered for the revised procedures. Testing methods and conclusions were validated with finite element models and structural health monitoring. This final report brings all aspects of the work together and recommends improved procedures and additional studies.

In 2018, the Minnesota Department of Transportation (MnDOT) constructed a pair of side-by-side bridges on TH 169 over Elm Creek, with glass fiber-reinforced polymer (GFRP) reinforcement used in one deck and conventional epoxy-coated steel reinforcement used in the other. To understand the behavior of GFRP reinforcement and compare the performance and durability of the GFRP- and steel-reinforced decks, the following efforts were undertaken: (1) collect structural behavior information and response characteristics of the two bridge decks under service loads; (2) examine the short- and long-term performance characteristics of the two bridge decks; and (3) assess the advantages of using non-conventional, corrosion-resistant deck reinforcement. From the outcome of this four-year monitoring program, both bridge decks behaved similar to each other and as expected. The GFRP-reinforced deck showed no unusual behavior or sign of deterioration compared to the steel-reinforced deck. Although similar patterns of surface and full-depth cracks were observed in both decks, the structural integrity of both bridges was found to be consistent with design specifications. The short- and long-term comparison of the decks indicated that the use of GFRP bars can be a promising alternative in bridge deck reinforcement.