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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.

The strength and durability of reinforced concrete (RC) bridges are adversely affected by the deterioration of their structural members. When investigating bridges in need of maintenance and repair, the deterioration due to the corrosion of steel rebars is commonly found to be a primary source of structural damage and degradation. To ensure the safety and performance of RC bridges while reducing their direct and indirect costs, an accurate estimate of the extent of reinforcement section loss has central importance for a wide spectrum of engineers and decision-making authorities. This research project investigated the steps required to achieve such rebar section loss estimates. To achieve this purpose, field assessments of rebar section loss were correlated with available predictive models and later calibrated to condition-specific field data. The outcome, which has been delivered in the form of steel reinforcement section loss guidance tables, directly contributes to understanding variability in rebar section loss when making loss predictions for use in structural evaluation. This facilitates planning preventive and/or corrective actions tailored to the condition state of deteriorating bridge elements.

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.