Interaction Between Patch Loading, Bending, and Shear in Steel Girder Bridges Erected with the Incremental Launching Method

In the incremental launching method (ILM), a bridge structure is assembled behind one of the end supports and moved longitudinally, passing by intermediate piers until it reaches the other end support. As the structure moves forward, the cantilever length increases until the launching nose reaches the next pier or abutment. In this process, at the cantilever support, the steel girders are subject to a combination of stresses due to the reaction force (or patch loading), major-axis bending, and shear. This loading condition, known as the M-V-P interaction, may lead to high stress concentrations that may cause local instability in the steel girder panels located at the cantilever support, principally due to the high web slenderness ratios. This paper presents the strain/stress measurements obtained from a steel I-girder bridge erected with the ILM. The instrumentation was positioned at three different locations along one of the I-girders to capture the stress variation, as the bridge was launched. These measurements serve as the basis to better understand the M-V-P interaction in steel girder bridges erected with this method. In addition, the field measurements are compared to available analytical models that predict this interaction in steel I-girder bridges erected with the ILM.

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