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Pretensioned concrete box beams have been used in highway bridges for more than half a century. Due to their geometry, they have often been used as a viable alternative to the classic I-shaped girders. Box beams are highly effective in cases where speed of construction is a priority. However, the detailing and design of box beams are more complicated than that of I-shaped girders. The flow of forces at the beam’s end blocks must be understood in order to detail reinforcement adequately. The following were the objectives of this research study: (i) quantify the demands placed on box beam end blocks upon prestress transfer, (ii) characterize the demands placed on box beam end blocks upon the application of superimposed loads, (iii) evaluate the effects of alternative void geometries at skewed ends of box beams on curing temperatures, (iv) based on the knowledge gained in (i), (ii) and (iii), improve the box beam end blocks, (v) test the improved end block under worst case scenario demands at prestress transfer and under extreme loading conditions, and (vi) validate currently used shear strength design methodologies in their application to pretensioned box beams. In order to achieve these objectives, an experimental program was conducted. The experimental program included the load testing of ten 4B28 and five 5B40 box beams, for a total of twenty nine load tests. The influence of several factors that distinguish box beam behavior from the better-understood I-shaped girder behavior was studied. Additionally, the experimental program included the fabrication, instrumentation and early-age behavior study of five 5B40 box beams. The first three beams were used to vii assess the behavior of box beams fabricated with the current TxDOT standard details (from December 2006). The fourth beam incorporated modifications to the standard reinforcement details based on the observations made through the study of the first three 5B40 box beams. The last specimen corresponded to a new box beam cross section (5XB40) optimized to be used in a spread-box beams configuration. / text

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Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 184-188). Also available via the Internet.

Thesis (M.S. in Engin.)--University of Texas at Austin, 1997. / Vita. Abstract. Includes bibliographical references (leaf 107).

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Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

The strength of 102 wood box columns of air-dry dense select southern pine was investigated in order to determine formulas for their design. Constructional variables such as column slenderness; plank thickness, fastening, and arrangement; and the use of spacers for individual plank stiffening were studied as to their effects on column strength. The analysis shows that those formulas currently used for the design of other column types are suitable for box column design if properly modified. Short box columns develop (1) a strength equal to that of solid columns of equal slenderness if of 2-in. Lumber and (20 85 percent of the solid column load if of 1-in. Lumber. The Euler formulas for long columns and the constant (K) in the fourth-power Forest Products Laboratory formula for intermediate columns must be revised to account for the load capacity of long box columns which is less than that of equivalent solid columns as a result of the lower stiffness of a nailed cross-section. The incorporation of box columns rather than solid columns in timber frameworks results in savings of material. Furthermore, with standard lumber sizes a wider variety of cross-sectional areas for box columns can be built than is possible with standard timber sizes for solid columns. / Master of Science

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