Our bridge team designed this bridge to replace a narrow multitruss structure spanning the Missouri River.
As a subconsultant, we provided design and plans for the river unit, which had spans of 300 feet, 426 feet and 300 feet with a 10-degree skew. The girders are parallel-flange, welded-plate girders with 132-inch webs. The river unit piers are hammerhead type with drilled-shaft foundations.
The load and resistance factor design (LRFD) included a structural steel weight optimization study for site-specific foundation analysis, which was the result of collaboration between the owner and geotechnical engineer. The drilled shafts for the river pier foundations are founded in shale. Due to the anticipated variations in the quality of shale, conservative values for end-bearing and side friction were recommended by the geotechnical consultant.
Because of the high number, large diameter and long lengths of the rock sockets, the team conducted Osterberg load tests on two production shafts. The test results allowed the team to shorten the rock sockets enough to offset the cost of the tests. The primary benefit of the tests was that the load capacity of the drilled shafts was field-verified.
Our experience in the design of Missouri River bridges was a key component of the design team’s credentials to perform the engineering for this project. We had previously completed design and construction services for three Missouri River bridge projects for which the Nebraska Department of Transportation served as the lead or a participating DOT.