Measurements of deformations and stresses due to plate out-of-flatness in a steel twin box girder bridge system
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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.