BNSF bridge replacement over Des Moines River
Hanson and a joint-venture partner provided BNSF Railway Co. with design services for the replacement of a bridge over the Des Moines River near Ottumwa, Iowa.
The existing bridge consists of five 140-foot, double-track truss spans with multiple 60-foot deck beam approach spans at each end. Three of the trusses spanned the Des Moines River with the other two spanning the westerly flood plain.
In phase one of this project, the Hanson team replaced the two 140-foot trusses over the flood plain with four 70-foot deck beam spans, adding a new pier support between the existing piers to reduce the span lengths. The new piers consisted of 10-foot-diameter drilled shafts installed on either side of the existing trusses. The piers were connected by a 10-foot-by-10-foot, cast-in-place concrete transfer beam.
Phase two of this project involved performing a value engineering analysis of the options for replacing the remaining three truss spans over the river. Analysis showed that the option of three new piers with two new 190-foot trusses and a 70-foot beam span would provide for a longer structure life, and it would improve the waterway opening of the Des Moines River when compared with reuse of the existing piers and construction of a new superstructure. During phase two, Hanson provided the design and prepared plans for these structures.
Some of the challenges associated with this project included maintaining track operations and using a ballasted deck bridge while maintaining existing low-steel elevations. Superstructure installation was performed during brief track shutdown periods of 24 hours for phase one and 36 hours for phase two.
During this project, Hanson also provided geotechnical analysis and foundation recommendations, bidding and construction assistance, and shop drawing review. Additionally, Hanson conducted the hydraulic and environmental studies, including wetlands, to get construction permitting from the U.S. Army Corps of Engineers.
The bridge was determined to have historic significance and was eligible for inclusion in the National Register of Historic Places — requiring a report and permitting from the Iowa State Historic Preservation Office.
In 2001, the other three 140-foot trusses and one 60-foot approach span were replaced with two new 190-foot trusses and a 70-foot deck beam span. This approach allowed the railroad to remove two large, deteriorated masonry piers from the river channel and replace them with only one new pier. This also reduced the restrictions in the channel and allowed for better water conveyance.
During construction, our team prepared construction cost estimates, coordinated with owner and contractor construction personnel, and performed shop-drawing review.