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Bridge-approach guardrail provides protection for vehicles from collision with bridge components, such as the blunt end of the bridge rail or abutment, and other types of run-off-the-road collisions. The primary objective of this research was to determine the average daily traffic (ADT) at which the benefit/cost ratio for the installation of approach guardrail at county-state-aid (CSAH) bridges in Minnesota becomes greater than 1.0. A survey of state transportation agencies found that 26 of 35 responding agencies have policies or guidelines requiring placement of approach guardrail on any bridge if the bridge was built using state funds. Results of the research analyses showed that bridge-approach guardrail was effective at reducing the severity of run-off-the-road crashes occurring on the approach or departure to CSAH bridges. Fatalities and A-injury crashes accounted for only 6 percent of the crashes occurring at bridges with approach guardrail compared to 28.5 percent at bridges without approach guardrail. The subsequent benefit/cost analysis showed that bridge-approach guardrail is cost-effective (i.e., B/C > 1) for CSAH bridges with ADT greater than or equal to 300 vehicles per day (vpd). Overall, approach guardrail has a benefit/cost ratio of approximately 3.5 to 5.5. The researchers recommended that the ADT threshold for approach guardrail on CSAH bridges be set at 400 vpd, which is consistent with previous Mn/DOT standards and AASHTO low-volume local road guidelines. Approach guardrail should be considered on a case-by-case basis for bridges with ADT between 150 and 400 vpd, especially those between 300 and 400 vpd. Placement of approach guardrail at bridges with ADT less than 150 vpd is not cost-effective in most cases.

Prior to 1985, it was common practice to avoid welding the connection plates to the tension flange of the girders of steel bridges. However, extensive fatigue cracking has developed in the unstiffened web gaps because of out-ofplane distortion. A new retrofit option was investigated that uses a room-temperature-cured two-part epoxy (3M Adhesive DP460-NS) to join a small length of 3/4-inch thick steel angle to the tension flange and the connection plate. A field test on two skewed bridges showed that the adhesive-angle retrofit system decreased the out-of-plane strain range by 40 to 50% when the original strain range was more than 50 microstrains. The ten adhesive-angle retrofits remained in place and were in good condition after three and a half years, suggesting that the chosen adhesive had good environmental durability. A laboratory large-scale specimen test with 8 web gaps showed that the retrofit system stopped or retarded most cracks even without stop holes when the measured out-of-plane strains were approximately 600 microstrains. Coupon tests conducted to investigate the environmental durability of the chosen adhesive showed that the chosen adhesive is suitable for applications at room or low temperature, even with high relative humidity.

The behavior of concrete integral abutment bridges was investigated through a field experiment and a numerical parametric study. The field investigation focused on Bridge #55555 in Rochester, Minnesota, which was monitored from November 1996 to February 2004. Over 150 instruments were installed during construction of the bridge to measure abutment horizontal movement, abutment rotation, abutment pile strains, earth pressure, pier pile strains, prestressed girder strains, concrete deck strains, thermal gradients, and weather. The collected data were used to understand the behavior of Bridge #55555 due to the effects of temperature, creep and shrinkage. Two live load tests were conducted in 1997 and 1999, to examine the behavior of the bridge under live load. The overall performance of the integral abutment bridge was good. Bridge shortening was observed from the readings of different sensors. A steadily increasing tendency of average pile curvatures was observed from the measured data. Possible reasons were investigated through a time-dependent numerical analysis. A 3D finite element model of the test bridge was developed which took into account soil-structure interaction. The model was calibrated using data collected from the truck tests and the data from the seasonal and daily temperature variations. A parametric study was conducted to extend the results of the test bridge to other integral abutment bridges with different design variables including pile foundation type, bridge span and length, and orientation and length of wingwalls. Several design recommendations are made regarding the temperature range, use of predrilled holes around the piles, pile analysis method, and the applications of simplified design approaches for concrete integral abutment bridges.

Multi-girder steel bridges are found as part of the transportation infrastructure of countries throughout the world. These bridges are typically constructed with a steel reinforced concrete deck rigidly attached to the top flange of steel girders. The deck and the transverse steel members distribute loads laterally between bridge girders. The weld connecting transverse stiffeners to the girder web are commonly terminated several inches away from the girder flanges to avoid overlapping with the web-to-flange connection weld, leaving a short, unstiffened portion of the girder web-the web gap. The large flexibility of the web gap region relative to the other components forces it to accommodate the majority of the distortion. Since 1998, several research efforts have investigated methods for predicting the amount of web gap stress a bridge will experience during its service life. Phase I of this research resulted in a simple equation for estimating web gap stress using data collected during field testing and subsequent finite modeling of a skew supported bridge with staggering bent-plate diaphragms. Phase II produced an approximate method for predicting diaphragm differential deflection of skew supported bridges with bent-plate diaphragms. The combined result of Phase I and Phase II was a useful method for predicting peak web gap stress in skewed multi-girder steel bridges with staggered bent-plate diaphragms. The next step was to develop a reliable procedure for the rapid assessment of distortional stresses in steel bridges that includes a test of the applicability of this procedure to bridges with geometries differing from those that formed the basis of the previous research. As a consequence of this most current research, the authors propose changes and recommend modifications of previously developed methods of field measurement and assessment.

A number of countries have incorporated precast components in bridge superstructures and substructures. Precast components include deck, abutment, and wall elements. Benefits of using precast elements in bridge construction include the high level of quality control that can be achieved in plant cast production compared to field cast operations and speed of construction afforded by the assembly of precast elements at the site rather than the time consuming on site forming and casting required in cast-in-place construction. Key components in the application of precast concrete to bridge structures are the connection elements. Connection details include the use of posttensioning systems, and various connection details such as weld plates, studs in grout pockets, and shear keys. The Minnesota Department of Transportation (Mn/DOT) constructed a bridge incorporating precast elements to enable rapid construction. The objective of this study was to develop an instrumentation plan to enable investigation of the performance of this bridge. Researchers developed an instrumentation plan based on information provided by the Mn/DOT bridge office regarding the specific bridge details and behaviors to be investigated. The instrumentation plan included the types and locations of the instruments.

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 Minnesota Department of Transportation (Mn/DOT) documented the appearance of excessive cracks in the reinforced concrete pier cap overhangs of State Highway Bridges 19855 and 19856. As a part of this study, the ultimate capacity of the pier cap overhangs was estimated by comparing predicted capacities calculated using standard design specifications to experimental results published in the worldwide literature. It was determined that the ultimate capacity of the pier cap overhangs was more than sufficient to assure that a cracked, but undeteriorated, pier cap is not prone to structural failure. An estimate of the initial cracking load of the pier cap overhangs was also created to determine what changes to pier cap design would be required to prevent future overhangs from cracking. It was determined that the depth of the overhangs would have to be increased by approximately 20% to prevent them from cracking. The changes to pier cap overhang design required to prevent cracking or meet recommendations to reduce crack widths may not be economically feasible. Therefore, other methods for controlling crack widths must were examined. An experimental study was conducted to investigate the use of externally bonded (EB) FRP sheets and near surface mounted (NSM) FRP tape for shear strengthening of reinforced concrete beams. This report describes the experimental program, presents the results of the study, and discusses the outcome of that investigation.

A total of 12 sealant products were applied on the Smith Avenue High Bridge in St. Paul and evaluated over a three-year period. Details, such as surface preparation and application methods, were documented for each product and are conditions specific to each product. Sealant performance was evaluated through field permeability testing, visual observations, and petrographic examination. Visual observations provided evidence that approximately 67 percent of test sections were performing effectively after one winter but only 4 percent after two winters. After three winters, 58 percent of the test locations were visually characterized as ineffective and 42 percent as partially effective. Product performance significantly reduced over the third winter, primarily due to major loss of sealant and surface sand materials. Coring was performed after the second winter, and the cores were photographed and subjected to a petrographic evaluation. The observed depth of sealant penetration was highly variable and likely is dependent on the presence of debris within the crack, original crack width, and the deck temperatures during application. The predominant failure mode observed under magnification was detachment from the crack face and not within the sealant materials. Based on numerous factors, four epoxy and three methacrylate products were recommended for consideration on MnDOT's Approved Products List. Each product recommendation contains the surface preparation and application method conditions under which they were applied. It is also recommended that MnDOT look into increasing the frequency of its routine crack sealing maintenance program from the current five-year cycle.

The Minnesota Department of Transportation has typically used epoxy-coated, straight-legged stirrups anchored in the tension zone as transverse reinforcement in prestressed concrete bridge girders. This configuration is readily placed after stressing the prestressing strands. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) specifications require stirrups with bent legs that encompass the longitudinal reinforcement to properly anchor the stirrups. Such a configuration is specified to provide mechanical anchorage to the stirrup, ensuring that it will be able to develop its yield strength with a short anchorage length to resist shear within the web of the girder. AASHTO specifications for anchoring transverse reinforcement are the same for reinforced and prestressed concrete; however, in the case of prestressed concrete bridge girders, there are a number of differences that serve to enhance the anchorage of the transverse reinforcement, thereby enabling the straight bar detail. These include the precompression in the bottom flange of the girder in regions of web-shear cracking. In addition, the stirrup legs are usually embedded within a bottom flange that contains longitudinal strands outside the stirrups. The increased concrete cover over the stirrups provided by the bottom flange and the resistance to vertical splitting cracks along the legs of the stirrups provided by the longitudinal prestressing reinforcement outside the stirrups help to enhance the straight-legged anchorage in both regions of web-shear cracking and flexure-shear cracking. A two-phase experimental program was conducted to investigate the anchorage of straight-legged, epoxy-coated stirrups, which included bar pullout tests performed on 13 subassemblage specimens that represented the bottom flanges of prestressed concrete girders, to determine the effectiveness of straight-legged stirrup anchorage in developing yield strains. Additionally, four girder ends were cast with straight-legged stirrup anchorage details and tested in flexure-shear and web-shear. The straight leg stirrup anchorage detail was determined to be acceptable for Minnesota Department of Transportation (MnDOT) M and MN shaped girders as nominal shear capacities were exceeded and yield strains were measured in the stirrups prior to failure during each of the tests.

Bridge scour is the removal of sediment around bridge foundations and can result in the failure of the bridge. Scour monitoring is performed to identify unacceptable scour on bridges considered to be scour critical and determine when scour reaches elevations that could cause potential bridge failure. Two types of monitoring are available: portable monitoring and fixed monitoring. Prior to this project, MnDOT was only using portable monitoring devices, which requires the deployment of personnel to make physical measurements of scour depths. For some scour critical bridges, especially during high-water events, fixed instrumentation capable of continuous scour monitoring was preferred, but MnDOT lacked the experience or expertise to install this type of equipment. This project installed fixed monitoring equipment at two bridge sites and monitored them for three years to determine the effectiveness and reliability of fixed scour monitoring deployments. Several device options were installed to allow MnDOT to analyze the installation and performance of different types of sensors. Both systems operated for the three years with some outages due to various causes but overall performance was acceptable. The outages were mostly related to power issues and communication issues. Valuable lessons were learned through the deployment, which may be applied to future installations. The deployment executed in this project has provided the confidence to deploy other fixed scour monitoring equipment at key bridges around the state of Minnesota. In addition, the data collected during deployment of the scour monitoring equipment has been stored and provides insight into scour processes. This data can be used by other research groups for design or research purposes.