Stresses in steel curved girder bridges

Steel curved I-girder bridge systems may be more susceptible to instability during construction than bridges constructed of straight I-girders. The primary goal of this project is to study the behavior of the steel superstructure of curved steel Igirder bridge systems during all phases of construction, and to ascertain whether the linear elastic analysis software used by MnDOT during the design process represents well the actual stresses in the bridge. Sixty vibrating wire strain gages were applied to a two-span, four-girder bridge, and the resulting stresses and deflections were compared to computational results for the full construction sequence of the bridge. The computational results from the MnDOT analysis software were first shown to compare well with results from a program developed specifically for this project (called the "UM program"), since the latter permits more detailed specification of actual loading conditions on the bridge during construction. The UM program, in turn, correlated well with the field measurements, especially for the primary flexural stresses. Warping stresses induced in the girders, and the stresses in the crossframes, were more erratic, but showed reasonable correlation. It is concluded that MnDOT's analysis software captures the behavior well for these types of curved girder bridge systems, and that the stresses in these bridges may be relatively low if their design is controlled largely by stiffness.