Project
A key element of the highway expansion project is the Lewis and Clark Bridge over the Missouri River. The existing bridge design included a two-girder steel superstructure, making it both fracture critical and infeasible to widen. However, having been just over 40 years old, there was potential for several more decades of use remaining. KLJ conducted an in-depth inspection of the bridge which revealed several small cracks in connections throughout the structure. Following the inspection, KLJ conducted both a fatigue analysis and life cycle cost analysis to compare rehabilitating the existing bridge and building a new two-lane bridge adjacent, versus building a four-lane bridge and removing the existing. Based on KLJ’s analysis, NDDOT chose the latter option.
Solution
The new bridge was designed to accommodate four lanes of traffic, including more than 2,500 trucks per day. The bridge length and clearance elevation were designed to accommodate a 100-year flood and also meet US Coast Guard navigational clearance requirements. This resulted in a six-span bridge approximately 1,520 feet long with main spans of 270 feet. The new bridge was designed using AASHTO LRFD specifications and includes continuous weathering steel, 102-inch deep plate girders with haunched approach spans, and driven pile foundations.
Results
The Lewis and Clark Bridge is the final segment of the overall US Highway 85 four-lane expansion project between the junction of US Highway 2 in Williston to south of Watford City, ND.
