Predicting the behavior of horizontally curved I-girders during construction

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Stith, Jason Clarence

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The majority of a bridge designer’s time is spent ensuring strength and serviceability limit states are satisfied for the completed structure under various dead and live loads. Anecdotally, the profession has done an admirable job designing safe bridges, but engineering the construction process by which bridges get built plays a lesser role in the design offices. The result of this oversight is the complete collapse of a few large bridges as well as numerous other serviceability failures during construction. According to the available literature there have been only a few attempts to monitor a full-scale bridge in the field during the entire construction process. Another challenge for engineers is the lack of analysis tools available which predict the behavior of the bridge during the intermediate construction phases. During construction, partial bracing is present and the boundary conditions can vary significantly from the final bridge configuration. The challenge is magnified for complex bridge geometries such as curved bridges or bridges with skewed supports.

 To address some of the concerns facing engineers a three span curved steel I-girder bridge was monitored throughout the entire construction process.  Field studies collected data on the girder lifting behavior, partially constructed behavior, and concrete deck placement behavior.  Additional analytical studies followed using the field measurements to verify the finite element models.  Finally, conclusions drawn from the physical and analytical testing were utilized to derive equations that predicted behavior, and analysis tools were developed to provide engineers with solutions to a wide range of construction related problems.  This dissertation describes the development of two design tools, UT Lift and UT Bridge.  UT Lift is a macro-enabled Excel spreadsheet that predicts the behavior of curved I-girders during lifting.  The derivation of the equations necessary to accomplish these calculations and the implementation are described in this dissertation.  UT Bridge is a PC-based, user-friendly, 3-D finite element program for I-girder bridges.  The basic design philosophy of UT Bridge aims to allow an engineer to take the information readily available in a set of bridge drawings and easily input the necessary information into the program.  A straight or curved I-girder bridge with any number of girders or spans can then be analyzed with a robust finite element analysis for either the erection sequence or the concrete deck placement.  The development of UT Bridge as well as the necessary element formulations is provided in this dissertation.



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