Browsing by Subject "Box girders"
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Item Measurements of deformations and stresses due to plate out-of-flatness in a steel twin box girder bridge system(2007-05) Espinoza, Omar Rene, 1983-; Helwig, Todd Aaron, 1965-Trapezoidal box girders are frequently used in curved bridge interchanges due to advantages in aesthetics, maintenance, and structural performance compared to comparable I-shaped girders. The smooth shape provides an aesthetic system and also results in fewer regions where corrosion causing agents such as moisture and debris collect thereby leading to decreased maintenance issues. The improved structural performance is due to the closed cross section that results in a large torsional stiffness which is important in curved bridge applications. Although there are several advantages to box girder system, the background and knowledge of the behavior of these systems is generally less than that of standard I-girders. One of the key elements of current studies, as well as the nature of this thesis, is the behavior of the slender plate elements that make up the box girder cross-section. Because of their wide and slender nature, the plate elements are susceptible to local instabilities. In addition, the formulation of excessive plate deformations due to construction processes, as well as loading, can have detrimental effects on the structural behavior of the plate elements. The objective of the research documented in this thesis is to document the impact of plate imperfections on the behavior of steel bridge box girders. Measurements of the stresses and deformations in the plate elements of a twin box girder bridge constructed at Ferguson Structural Engineering Laboratory were carried out during construction and subsequent simulated live loading. Stress patterns are compared with imperfection measurements to document the impact on the girder behavior. This study is part of a larger project sponsored by the Texas Department of Transportation regarding plate tolerances. The measurements from this study will be used to validate finite element modeling techniques for studies on the impact of plate imperfections on the girder behavior. Data presented in this thesis will be combined with field measurements and computational results to help establish fabrication tolerances for plate out-of-flatness in steel bridge girders.Item Shear performance of ASR/DEF damaged prestressed concrete trapezoidal box bridge girders(2010-08) Wang, Tz-Wei; Jirsa, J. O. (James Otis); Bayrak, Oguzhan; Ghannoum, Wassim M.; Wheat, Harovel G.; Zhu, JinyingConcrete bridges in Texas have developed large cracks in bent caps and pretensioned trapezoidal bridge girders. The bridges show premature concrete deterioration due to alkali-silica reaction (ASR) and delayed ettringite formation (DEF). There is concern that deterioration due to ASR/DEF may lead to a loss of structural capacity. However, there are no quantitative guidelines to relate the level of concrete deterioration due to ASR/DEF to structural performance. Using such guidelines, the need for rehabilitation of beams with ASR/DEF cracking can be assessed. The goal of this research was to determine the shear capacity of pretensioned trapezoidal box girder specimens exhibiting varying degrees of ASR and/or DEF cracking and to use the shear testing results to evaluate the severity of the problem that may exist in Texas bridge structures. To achieve this goal, beams that were severely deteriorated due to ASR/DEF over a period of more than ten years were transported to the University of Texas for testing to failure. Both severely deteriorated and uncracked beams were tested in shear. The test results were used to evaluate the shear performance of trapezoidal box beams affected by ASR/DEF. In addition, three different types of forensic analyses were conducted on the beams to understand the nature of the ASR/DEF cracks and severity of the deterioration. After testing, it is found that the shear capacity of the test specimens was not significantly reduced even with heavy ASR/DEF cracking. Assessment using current US design provisions for bridges or buildings (ACI 318-08 and AASHTO LRFD 2008) and the proposed provision from an earlier project (TxDOT Project 5253) yielded conservative estimates of strength. Results from forensic analyses provided a qualitative indication of ASR/DEF damage but did not correlate with the observed levels of ASR/DEF deterioration.