A Prestressed Concrete Railroad Bridge on the Prairie

Abstract

• ying in the center of North Dakota, just a short distance north of Fort Lincoln (where General Custer began his fateful journey to the Little Bighorn), the historic city of Mandan has preserved its, Old West legacy, in part, through an extensive renovation of Fort Lincoln. Situated at the intersection of Interstate 94 and the Missouri River, Mandan is also known as a railroad town. Indeed, the town has one of Burlington Northern's major switching yards located in the heart of the city. The confluence of these railroad tracks and the traffic between Fort Lincoln and Mandan has brought about the construction of the first prestressed concrete railroad bridge in North Dakota. Built in 1943, the original underpass on North Dakota's Highway 1806 allowed for only two lanes of vehicular traffic, and the vertical clearance of the structure restricted its use by many trucks. However. the decision to replace the old structure posed several problems for the designers. • The existing structure was located on the mainline of the Burlington Northern Railroad. Coal trains, many 100 units in length or longer, used the tracks each day. Therciore, it was imperative that traffic be maintained on three tracks at all times during the construction period. • Elevation changes would not he allowed in the new design. The site is at the end of Burlington Northern's switching yard: large displacements of the tracks would not be feasible. • The existing underpass surface elevation was only 2 ft (0.t+1 in) above the ground water. To provide adequate vertical clearance, the new roadway had to be built below the water table. • In 1989, North Dakota residents would he celebrating the state's centennial anniversary. The crowds expected for the July celebration could triple the normal population of Mandan. and a major construction project would not be allowed in the downtown area at this time.