Bridge 207 is a two-span horizontally curved steel plate girder bridge near Port Matilda, Pennsylvania. Although the curvature is not severe, the curvature combined with the unequal span balance caused an unusual distribution of force effects in the girders. A global twisting of the superstructure was caused by the unequal vertical deflections in the two spans. The computer program BSDI-3D was used to analyze the curved superstructure. To account for the out-of-plumb condition of the girders in their final condition, additional lateral flange bending moments were calculated. The magnitude of the additional lateral moments was a function of the vertical bending moments and the degree of twist in the girder. Field monitoring of the structure is focusing on the effects of curvature during construction. This is being accomplished by developing a detailed time line of superstructure erection and deck placement and through monitoring of the bridge by using vibrating wire strain gauges and tiltmeters positioned at critical locations on the girders and cross-frames. Field data were recorded before and after critical construction events, such as girder erection, cross-frame and formwork placement, and the deck pour. This information is being used to determine the effects of curvature on the cross-frames during construction by using axial stresses and strains and on the girders by using warping stresses and strains.
