Technical Reports, Civil and Environmental Engineering

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Browsing Technical Reports, Civil and Environmental Engineering by Subject "Anchorage zone reinforcement"

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    Anchorage Zone Design for Pretensioned Precast Bulb-T Bridge Girders in Virginia
    E.D. Crispino; Cousins, Thomas E.; Roberts-Wollmann, Carin L. (Virginia Center for Transportation Innovation and Research, 2009-06-01)
    Precast/prestressed concrete girders are commonly used in bridge construction in the United States. The application and diffusion of the prestress force in a pretensioned girder cause a vertical tension force to develop near the end of the beam. Field surveys of the beam ends of pretensioned bridge girders indicate that many of the precast bulb-T (PCBT) beams used in Virginia develop cracks within the anchorage zone region. The lengths and widths of these cracks range from acceptable to poor and in need of repair. Field observations also indicate deeper cross sections, very heavily prestressed sections, and girders with lightweight concrete tend to be most susceptible to crack formation. This research examined a new strut-and-tie based design approach to the anchorage zone design of the PCBT bridge girders used in Virginia. Case study girders surveyed during site visits were used to illustrate the nature of the problem and support the calibration of the strut-and-tie-based model. A parametric study was conducted using this proposed design model, and the results of this study were consolidated into anchorage zone design tables. The results of the parametric study were compared to the results obtained using existing anchorage zone design models, international bridge codes, and standard anchorage zone details used by other states. A set of new standard details was developed for the PCBT girders that incorporates elements of the new design approach and is compatible with the anchorage zone design aids. A 65-ft PCBT-53 girder was fabricated offsite and tested at the Virginia Tech Structures Lab to verify the new strut-and-tie-based design model. This girder contained anchorage zone details designed with the new model. The new anchorage zone details were successful at controlling the development of anchorage zone cracks. The new design approach is recommended for implementation by the Virginia Department of Transportation.
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    Live Load Test and Failure Analysis for the Steel Deck Truss Bridge Over the New River in Virginia
    Hickey, Lucas; Roberts-Wollmann, Carin L.; Cousins, Thomas E.; Sotelino, Elisa; Easterling, William Samuel (Virginia Center for Transportation Innovation and Research, 2009-05-01)
    This report presents the methods used to model a steel deck truss bridge over the New River in Hillsville, Virginia. These methods were evaluated by comparing analytical results with data recorded from 14 members during live load testing. The research presented herein is part of a larger endeavor to understand the structural behavior and collapse mechanism of the erstwhile I-35W bridge in Minneapolis, Minnesota, that collapsed on August 1, 2007. Objectives accomplished toward this end include investigation of lacing effects on built-up member strain measurement, live load testing of a steel truss bridge, and evaluation of modeling techniques in comparison to recorded data. The most accurate model was used to conduct a failure analysis with the intent of then loading the steel truss bridge to failure. Before any live load testing could be performed, it was necessary to confirm an acceptable strain gage layout for measuring member strains. The effect of riveted lacing in built-up members was investigated by constructing a two-thirds mockup of a typical bridge member. The mockup was instrumented with strain gages and subjected to known loads to determine the most effective strain gage arrangement. The results of the testing analysis showed that for a built-up member consisting of laced channels, one strain gage installed on the middle of the extreme fiber of each channel's flanges was sufficient. Thus, laced members on the bridge were mounted with four strain gages each. Data from live loads were obtained by loading two trucks to 25 tons each. Trucks were positioned at eight locations on the bridge in four different relative truck positions. Data were recorded continuously and reduced to member forces for model validation comparisons. Deflections at selected truss nodes were also recorded for model validation purposes. The model validation process began by developing four simple truss models, each reflecting different expected restraint conditions, in the hopes of bracketing data from recorded results. The models included a simple truss model, a frame model with only the truss members, and a frame model that included the stringers. The final, most accurate model was selected and used for a failure analysis. This model showed where the minimum amount of load could be applied to learn about the bridge's failure behavior and was to be used for a test to be conducted at a later time. Unfortunately, the project was terminated because of a lack of funding before the actual test to failure of the steel truss bridge was conducted. Nevertheless, findings from the study led to two important recommendations: 1.) When instrumenting a steel truss bridge for load testing by placing strain gages on built-up members, four gages, one placed on each flange of each channel, should be used. 2.) When modeling deck truss bridges, the system should be considered to be a frame and should include the stringers in the model.