published_or_final_version / Civil Engineering / Master / Master of Philosophy

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Thesis (M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ. 202-207)

Thesis (Ph.D.) - University of Glasgow, 1999. / Ph.D. thesis submitted to the Department of Civil Engineering, University of Glasgow, 1999. Print version also available.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references (p.195-207).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisors: Sharon L. Wood and Ned H. Burns. Vita. Includes bibliographical references.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed May 8, 2007). PDF text: iii, 251 p. : ill. (some col.) ; 2.75Mb UMI publication number: AAT 3237783. Includes bibliographical references. Also available in microfilm and microfiche formats.

Doctor of Philosophy / Department of Civil Engineering / Robert J. Peterman / A comprehensive study was conducted to determine the variation in transfer length of pre-tensioned prestressed concrete railroad ties with different parameters, including prestressing steel type and concrete variables. The in-depth evaluation included different prestressing reinforcement types that are employed in concrete railroad ties worldwide. The study consisted of two phases; Lab-Phase and Plant-Phase. Throughout the study, transfer lengths were determined from surface strain measurements of pre-tensioned concrete members. During the Lab-Phase, pre-tensioned concrete prisms were fabricated to replicate plant manufactured crossties. Different groups of prisms were fabricated during this phase, with each group used to determine the influence of selected prestressing steel or concrete variables on transfer length. A special jacking arrangement was employed to ensure that each of the reinforcements was tensioned to the same force. During the Lab-Phase, an 8-inch Whittemore gage was utilized to determine concrete surface displacements and thereby calculate surface strains. Later, during the Plant-Phase, pre-tensioned concrete railroad ties were fabricated at a concrete crosstie manufacturing plant with the same group of reinforcements. In-plant concrete surface strains were determined by utilizing both the Whittemore gage and two automated laser-speckle imaging (LSI) devices. Later, a long-term study was conducted on plant-manufactured crossties that were cast exclusively to utilize the mechanical (Whittemore) gage system. Various results from both the Lab-Phase and Plant-Phase are presented along with discussion. Potential benefits of laboratory prisms in estimating transfer lengths is also discussed. Results from both phases indicated that large variations in transfer lengths are due primarily to variations in the bond quality of the different prestressing tendons and the concrete strength at detensioning. Results pertaining to the variation in bond quality due to other concrete variables are also presented.

The present approach to the design of prestressed beams is antiquated and time consuming. Neither SLS or ULS requirements are satisfied directly. There is a need for a new approach using plastic principles to design the prestressing requirements at ULS considering a whole span at a time, with checks made for SLS requirements afterwards. For a plastic design, the designer would need to know the limits of the bending moment redistribution for the beam under consideration. An equation is therefore necessary to assist the designer in this regard. Such an equation should take into account the cross-section shape of the beam and the prestress to reinforcing steel ratios. Many examples would have to be investigated using a rigorous plastic analysis to formulate such an equation. A computer program has been written as part of this thesis to perform such a rigorous analysis. It's accuracy has been evaluated by comparison with laboratory test beam results. The comparison was favourable, although more results would have to be compared to establish the accuracy that could be expected. A few examples were investigated and the observations noted. Two extreme cases were examined, those of a T-beam and I-beam. The redistribution of bending moments was similar in both cases, but the percentage of the central moment capacity reached was considerably less for the T-beam. For both beams it was impossible to reach the ultimate capacity at the centre before the strain capacity at the supports was exhausted. It was concluded that a plastic design procedure should be introduced, based on the ULS capacity of a span at a time. SLS requirements could then be checked afterwards. This approach would provide a design procedure corresponding to those used for other forms of modern structural design and would be much quicker, safer, more accurate and less costly that the existing design procedures.

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