Instrumentation of a Horizontally Curved Steel I-Girder Bridge during Construction

Horizontally curved, steel I-girder bridges can present unique challenges for engineers and contractors because the curved geometry can result in a complicated torsional response. The most complicated stages for predicting behavior of the girders usually occur during erection and construction when the loads and support conditions are the most unpredictable. Although laboratory experiments can provide valuable insight into the behavior, the high cost of the specimens often precludes meaningful experiments, whereas field monitoring of bridges during construction provides invaluable opportunities to understand the behavior and gather data for validating computational models. A horizontally curved, steel I-girder bridge was instrumented to monitor the bridge during erection and concrete deck placement. Stresses were monitored as girders were lifted into position, followed by measurements of vertical deflections, rotations, and stresses during the concrete deck placement. The stresses during the erection process were relatively low owing to the proper use of lifting and placing methods; however, high stresses can be induced after girders are placed when the cross frames are ratcheted into position. As expected, higher stresses, compared with the steel erection process, were recorded during the concrete deck placement. Nonetheless, the monitored bridge did not have stability problems because the bridge utilized a relatively stocky flange width-to-depth ratio. For bridges more susceptible to stability challenges, such as tightly curved bridges, highly skewed bridges, narrow bridges, bridges with odd span arrangement, or some combination of these attributes, it is recommended that the designer consider the implication of slender girders and explicitly design for the possibility of construction-related stability challenges. In addition, resulting from the limited availability of field measurements of horizontally curved girders throughout the construction process, the data represent a valuable resource researchers can use to validate computational models for conducting parametric investigations. This paper outlines the methods used during the field monitoring and summarizes the results from the field measurements.