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Their initial curvature make steel-cured girder bridges more susceptible to lateral-torsional bucking during construction. Critical in assessing the strength and fatigue life of the bridge components, predicting stresses in the main girders and the crossframes proves more complex than in straight bridges. In this project, researchers investigated the correlation between measured and computed results in a two-span, four-girder, continuous composite steel curved girder bridge with skew supports. A previous phase involved computing the stresses through a linear elastic grillage finite element computer project and comparing the results with a typical third-party curbed girder analysis program. The project's second phase further investigated the correlation between measured and computed stresses by running two additional live load tests on the bridge. This report summarizes research to investigate the behavior of the curved girder bridge system through all phases of construction, as well as to a series of live load field tests. In addition, researchers investigated the effects of change in temperature on the bridge behavior and tracked any changes in behavior of the bridge system over time and under service load conditions.

This report investigates a method of repairing fatigued steel bridge girders using carbon fiber reinforced polymer (CFRP) strips. This type of repair would be used to prevent the propagation of cracks which could lead to failure of the bridge girders. The main advantage of using CFRP is it is lightweight and durable, resulting in ease of handling and maintenance. Therefore, it would not require the closing of traffic on the bridge during rehabilitation. Effective bond length was determined by a series of experimental tests with actual materials, as well as through the use of analytical equations. Finally, tests were conducted on full-scale cracked girders; the application of the CFRP strips to the steel girders resulted in significant strain reduction, except in the case of small cracks where it was difficult to clearly identify the benefits.

Traffic signs and signals are often supported by flexible cantilevered structures that are susceptible to wind-induced vibration and fatigue. The latest version of the design specifications published by the American Association of State Transportation Officials (AASHTO) now considers fatigue as a limit state. However, most of the fatigue classifications for welded details were not based on full-scale testing, and are thought to be overly conservative. This research will address the fatigue resistance of two common mast arm-to-pole connections used in the state of Minnesota. The resistance attained experimentally aligned with current predictions using AASHTO procedures, except for in-plane loading of box connection details. As a consequence of specimen design, a variety of tube-totransverse plate connections were also tested using multi-sided tube cross-sections with different tube diameters, tube thicknesses, as well as base plate thicknesses. The standard tube-to-transverse plate connection exhibited Category K2 resistance, two categories lower than the E' specified by AASHTO. This resistance was enhanced to Category E' through impact treatment or Category E by doubling the base plate thickness. Gusset plates could not prevent cracking of the tube at the base plate, but the tips of the gusset plate exhibited Category E resistance.

This study sought to determine the dominant parameters that lead to premature transverse cracking in bridge decks and to make recommendations that help reduce cracking tendency in bridge decks. The project includes two main parts: a field study and a parametric study. The field study identified 72 bridges in the Minneapolis/St. Paul area and explored the correlation between the observed cracking of those bridges and available design, material, and construction-related data. The parametric study investigated the relative influence of the factors that affect transverse deck cracking through a controlled nonlinear analysis study. Variables included: shrinkage, end restraint, girder stiffness, supplemental steel bar cutoff, cross frames, splices, deck concrete modulus of elasticity, and temperature history. In addition, four bridges from the companion field study were modeled to compare the analytical results with the actual crack patterns. Based on these results and correlation with other research, the study identified the following dominant factors affecting transfer cracking: shrinkage, longitudinal restraint, deck thickness, top transverse bar size, cement content, aggregate type and quantity, air content, and ambient air temperature at deck placement. Recommended practical improvements to bridge deck construction, in order of importance, include: using additives to reduce shrinkage of the deck concrete, using better curing practices, and minimizing continuity over interior spans.

Steel curved I-girder bridge systems may be more susceptible to instability during construction than bridges constructed of straight I-girders. The primary goal of this project is to study the behavior of the steel superstructure of curved steel I-girder bridge systems during all phases of construction, and to ascertain whether the linear elastic analysis software used by Mn/DOT during the design process represents well the actual stresses in the bridge. Sixty vibrating wire strain gages were applied to a two-span, four-girder bridge, and the resulting stresses and deflections were compared to computational results for the full construction sequence of the bridge. The computational results from the Mn/DOT analysis software were first shown to compare well with results from a program developed specifically for this project (called the "UM program"), since the latter permits more detailed specification of actual loading conditions on the bridge during construction. The UM program, in turn, correlated well with the field measurements, especially for the primary flexural stresses. Warping stresses induced in the girders, and the stresses in the crossframes, were more erratic, but showed reasonable correlation. It is concluded that Mn/DOT's analysis software captures the behavior well for these types of curved girder bridge systems, and that the stresses in these bridges may be relatively low if their design is controlled largely by stiffness.

Current techniques for rating of horizontally curved composite steel I-girder bridges often use approximate methods of analysis based on assessment of individual straight girders with altered properties to account for member curvature. This project investigates the behavior and rating of these bridges through load testing with heavy trucks. A five-span continuous two-girder horizontally curved steel I-girder bridge was load tested. Strain and displacement measurements were obtained for the main girders, diaphragms, lateral wind bracing, bearings, composite interaction, and areas of high strain concentrations near stiffener details. Forty-three static tests with different truck load patterns were conducted along with thirteen dynamic tests to assess the bridge response. A linear elastic grillage-based model of the bridge was used to simulate the load patterns. A sensitivity study was carried out based on the tested bridge along with simulations of two other bridges previously tested elsewhere so as to assess the robustness of grillage analysis for use in load rating of horizontally curved steel I-girder bridges. Recommendations are made outlining rating of horizontally curved composite steel I-girder bridges through the use of grillage-based analysis, with and without the use of load testing, and within the context of the AASHTO Load and Resistance Factor Rating (LRFR) and Load Factor Rating (LFR) procedures.

A vertical-lift bridge, the Stillwater Bridge, Bridge 4654, opened in 1931 across the St. Croix River between Minnesota and Wisconsin. To assess the remaining fatigue life of this bridge, strain gages were installed on an interior floorbeam and on a tension chord of a typical through truss span. The maximum stress range was 32 MPa at the centerline of the floorbeam. The measured data were rationalized by performing an analysis of the floor system and truss. The greatest ratio of the maximum expected stress range (18 MPa) to the fatigue strength (31 MPa) is at the centerline of the severely floorbeams located at the ends of the spans. Therefore, fatigue cracking is not expected in the steel members of a typical truss and taking the trucks off the bridge will have no significant effect on the fatigue life of the steel members in a typical through truss span. As a staff paper, this publication is intended for internal use by the Minnesota Department of Transportation (Mn/DOT). Distribution is limited