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Behavior of Horizontally Curved Steel I-Girders During Construction

Farris, Jamie

2008

Elevated direct connector bridges have become a frequent solution to moving traffic from one highway to the next at efficient operating levels, without disturbing the underlying roadways and businesses. Horizontally curved I-girders provide a means to build longer spans with complex roadway geometry. With the increasing use of curved Igirders, their behavior is of paramount concern during the critical construction stages of erection and concrete deck placement. Preferred practices for TxDOT steel bridges recommend girder proportions that are conservative with respect to the American Association of State Highway and Transportation Officials (AASHTO) minimum requirements; however the State of Texas also has a good record with respect to safety of the girders during erection and construction. Many of the TxDOT preferred practices are based upon past experience without research justification. An accurate evaluation of the construction sequence of curved steel I-girders requires in-depth knowledge about stability, phasing, support conditions, composite action, and concrete curing time and temperature. The nature of the curved geometry causes warping stresses in the members in addition to the bending stresses. The interaction between warping and bending stresses complicates the design and the erection process for curved bridges.

The critical construction stages of girder erection and concrete deck placement are discussed and evaluated in this thesis. Field studies were performed during the construction of a concrete bridge deck and the data captured from that investigation provide valuable information to validate finite element models. Field data during concrete placement are presented and discussed in this thesis. In addition, a parametric study for the lateral-torsional buckling of non-prismatic curved I-girders during lifting was also performed. The trends from the analysis results are evaluated and discussed. Finally, in order to capture actual curved I-girder erection situations, a questionnaire was developed and sent to erection construction contractors, inspectors, and engineers in Texas and around the United States. The responses from the questionnaire are presented in this thesis.

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