Government Swing Bridge Rehabilitation

Completed in 1896, and fully operational today, the double-deck highway/railroad swing bridge was the first bridge designed by Modjeski and Masters (M&M) founder Ralph Modjeski. The current crossing is the fourth bridge installment at Rock Island Arsenal – replacing three others that were constructed beginning in the early 1850s. In recent years, the useful fatigue life of the Government Bridge was considered exhausted and the bridge was scheduled for replacement by the stakeholders. However, our problem solvers believed that a more sustainable alternative to replacing the historic swing bridge could be found.

Working with the U.S. Army Rock Island Arsenal Department of Public Works, M&M's technical experts performed a new fatigue study which included a comprehensive review of historical train loading on the bridge. We also installed strain gages on fracture-critical members to compare actual stress ranges with theoretical values. Our analysis showed that the bridge had only used a small portion of its useful fatigue life, confirming our belief that the bridge could be cost-effectively rehabilitated. Next, our knowledgeable structural, electrical, and mechanical engineers used the latest Illinois DOT Standard Specifications, in conjunction with the AREMA Manual, for the rehabilitation design of construction repairs. As active partners, M&M led a series of rehabilitation assignments to maintain this long-standing connection. We completed analysis of strain gage data for the fatigue study, performed a load rating of the truss and highway/rail floorsystems, and provided services to improve vertical clearance of the end portals. Collectively, our experienced engineers designed various structural, mechanical and electrical details for the successful rehabilitation of the bridge, including upgrades to and replacement of the bridge’s movable machinery and drive system.

Bridge Geometry
Length of Main Span 365 Feet
Total Project Length 1,850 Feet
Lanes on Structure Two Lanes; two railroad tracks

Where else can you find something that's 120 years old and still doing what it was designed to do?

- R. Mike Dunne, Bridge Supervisor