Live Load Stresses in Steel Curved Girder Bridges

Project summary:

In 1995, the PI and his colleagues, T. V. Galambos and R. T. Leon, and their students, instrumented MnDOT bridge no.7998, a two-span, four girder, steel curved girder bridge, with Geokon vibrating wire strain gages to determine comprehensively whether the stresses induced in the bridge during construction and live loading were reproduced accurately by the analysis program DESCUS, which is currently used by MnDOT for analyzing steel curved girder bridges (MnDOT Agreement No. 72443). The researchers confirmed that the analysis program and field measurements, along with the results from a related analysis program developed at the University of Minnesota for this project, matched quite well. These gages are suitable for long term measurement, since they do not lose their bond to the steel or their zero reading over time, and they are resistant to large temperature variations. The current project is a continuation of this previous research project. The primary objective of this research is to measure, once per year for three years, the strains and stresses due to substantial truck live loading on this bridge. These readings will provide an indication of whether or not there are significant changes in stiffness or composite action of the bridge over time, thus providing insight into the long term behavior of steel curved girder bridge systems. The University of Minnesota analysis program developed for the original steel curved girder project will be used to correlate with the field readings taken for the live loading. A set of readings will be also taken to assess the effect of daily temperature variation on the strains in steel curved girder bridges of this sort. In addition, several extra strain gages may be placed on the bridge if possible, so as to gather further information regarding, for example, the stresses in the crossframes of the bridge.