The Extradosed Prestressed Bridge represents a relatively new bridge type. The first of this type bridge was constructed in Japan in 1994, and Japan has since built at least 29 examples of this bridge type. Throughout the rest of the world, another 34 of this bridge type have been built, with most countries having only one, or at most a few, examples. A broader application of this bridge type has been hampered by lack of design information and in particular lack design criteria for the stay cables. The purpose of this dissertation is to progress the understanding and application of this bridge type by providing (1) a summary and discussion of extradosed bridges constructed worldwide, (2) an assessment and recommendations on proportioning parameters, characteristics and features of extradosed prestressed bridges, and (3) a contribution of a new design approach for the stay-cable design for extradosed prestressed bridges. Also presented is an application of the above to a real-world prototype design to assess and comment on the application of the recommended proportioning parameters, characteristics, features and the new approach to stay cable design criteria.

An experimental study was conducted at the Ferguson Structural Engineering Laboratory in order to investigate the shear behavior of 54-inch deep prestressed concrete U-beams. The primary goal of this research was to improve the design and detailing of the skewed end-blocks commonly used in these beams. As U-beams had been in service for several decades without incident, it was anticipated that there would be little need for change in the design, and the findings of the research would involve a slight tweaking to improve the overall performance. Unfortunately, during the first phase of shear testing (testing of the current design standard) it was found that the U-beam was not reaching the code calculated shear capacity. During this phase of testing the premature failure mechanism was isolated as the breakdown of the web-to-flange interface in the end region of the girder. Therefore, the second phase of testing sought to prevent the breakdown of this boundary by three options: (1) increasing the web width while maintaining current levels of mild reinforcement, (2) increasing the web width while also increasing the amount of reinforcement crossing the web-to-flange boundary, or (3) by increasing the amount of reinforcement at the boundary while maintaining the current web width. Two acceptable solutions to the premature failure method were developed and tested during this phase both of which included an increase in the amount of mild reinforcement crossing the web-to-flange interface (with and without an increase in web width). The research into refining of these new details is ongoing as part of the Texas Department of Transportation’s Research Project number 0-5831. / text

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Development of shear databases attracted a great deal of attention in the shear research community within the last decade. Although a few shear databases have already been developed by several research groups, there is no comprehensive shear database that is focused on prestressed concrete members. This thesis aims to develop a shear database for prestressed concrete members with an intensive literature review. This literature review resulted in a database that contained a total of 1,696 tests reported in North America, Japan, and Europe from 1954 to 2010. The database was used to evaluate shear design provisions available in North America, Japan, and Europe. The variations in measured versus calculated shear strength using twelve shear design equations were analyzed. The analysis results indicated that design expressions based on the Modified Compression Filed Theory (MCFT) produced the best performance to estimate the shear strength of prestressed concrete members with sufficient shear reinforcement. The MCFT-based design expressions, however, provided unconservative strength estimations for members that failed in shear but exhibited signs of horizontal shear damage and/or anchorage zone distress. The ACI 318-08 detailed method was found to be less conservative than the MCFT-based design expressions. Additionally, on the basis of a careful examination of test results included in the database, a new limit for the minimum shear reinforcement was proposed. The database was also used to investigate the shear behavior of prestressed concrete members. This investigation revealed that there was no evidence of size effect in the shear strength of prestressed concrete members with sufficient shear reinforcement. Additionally, it was found that prestress force and shear reinforcement increased the shear strength although there was an upper limit on the effectiveness of shear reinforcement. / text

Split Concrete Model (SCM) is a unified approach towards modeling shear behavior in concrete. SCM is essentially a rational model which is evaluated and modified using a large experimental database.The shear strength of the concrete beam is modeled as the sum of the contribution of concrete, transverse reinforcement, longitudinal reinforcement and bond between concrete and longitudinal reinforcement. Concrete does not contribute to the shear strength after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the second branch of the critical crack while computing the contribution of concrete towards shear strength of the beam. Formation of the second branch of the critical crack and immediate subsequent failure of the beam has been compared to the split-cylinder test, which forms the conceptual basis of SCM.SCM computes the concrete contribution using the split tensile strength and the area under compression of the concrete beam. For cases where a split-cylinder test is not performed, a mathematical model is proposed to compute the split tensile strength using the compressive strength of concrete available from experimental results. This model is proposed using advanced statistical methods, including weighted residuals and Box-Cox transformation and is validated using various statistical procedures. The transverse reinforcement contributes to the shear strength of the concrete beam only after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the first branch of the critical crack while computing the contribution of the transverse reinforcement towards shear strength of the beam, instead of the conventional approach of considering the entire length of the crack. The contribution of the longitudinal steel and bond between concrete and longitudinal steel and concrete is accurately modeled unlike the conventional approaches which do not consider this contribution.Evaluation using the database shows that SCM can predict accurate results for all ranges of strength, depth, reinforcement ratio, and shear span to depth ratio of the beam. This shows that all the influencing parameters for concrete shear strength have been correctly modeled in SCM. SCM gives more accurate results as compared to current codified approaches as verified with design examples. Finally, specific recommendations have been made indicating how the shear design requirements in the current ACI code can be modified.

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Thesis (M.App.Sc.) - Carleton University, 2002. / Includes bibliographical references (p. 108-112). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 306-312). Available also in a digital version from Dissertation Abstracts.