The Susquehanna River Bridge, which was built in 1904, is a double track bridge with a total length of 4153'-8" between backwalls of abutments. The bridge consists of one deck truss span of 197'-2" at the Perryville end followed by eight deck truss spans of 260'-0" each, one through truss swing span of 280'-0", seven deck truss spans of 200'-0" each, and one deck truss span of 196'-0" at the Harve de Grace end of the bridge. This open deck bridge carries two electrified tracks with high speed trains.

Modjeski and Masters assessed structural members in the Pratt Deck Truss spans. Strain gage measurements on structural members of four deck truss spans and the swing span were made to evaluate the bridge for its capacity to carry coal trains with cars loaded to a gross weight of 286,000 lb. (286 K), in contrast to the normal gross-weight limit of 265 K. Additionally, the measurements were made to provide baseline data relevant to later retrofits, and to assess the performance of retrofits installed and lubrication maintenance conducted at selected bottom and top chord joints.

Gage locations for determining stresses were generally selected on the basis of inspection data, discrepancies between prior measurements and modeling results, retrofit actions, and experience. Data was obtained for selected lower chord eyebars, diagonal eyebars, top chords, stringers, floorbeams, and vertical posts.

The study determined the benefit of corrective measures, even with 263 K K-car trains. Foremost among the findings were: Bending stresses in excess of the axial stresses that occurred in the lower-chord eyebars adjacent to abutments, indicating considerable pin restraint at the panel points. The studies also showed previous fatigue retrofits have been effective in arresting previous fatigue cracks.