Merchants Bridge Main Span Truss Replacement & East Approach Retrofit

The Merchants Bridge, a critical crossing over the Mississippi River in St. Louis, Missouri, had served as a vital transportation link for over 127 years. However, by the time the project began, the bridge had exceeded its design life. The main span trusses, built in 1890, and the east approach structures were deteriorating, and the bridge was experiencing operational challenges. These included speed, clearance, and load restrictions that impacted the efficiency of one of the nation’s primary east-west rail corridors. With an average of only 38 daily train crossings, the bridge’s limitations were causing increased operational costs for the Terminal Railroad Association of St. Louis (TRRA) and the six Class I freight railroads that relied on this essential crossing.

Our solution involved the replacement of the main span trusses and east approach retrofitting to restore the bridge’s operational capacity, extend its lifespan, and revitalize this historic crossing.

Our team led the design for the reconstruction of the Merchants Bridge, including the replacement of the three main span trusses, seismic retrofitting of the four river piers, and significant improvements to the east approach. The project focused on enhancing the bridge’s structural integrity, increasing load-bearing capacity, and improving operational efficiency.

• Main Span Truss Replacement: The three 520-foot river-span trusses were replaced to address the aging structure and meet modern demands. Key tasks included strengthening the truss chords for removal, reinforcing the piers, and coordinating a gantry system for lifting and sliding the new spans into place. To minimize disruptions, the replacement of each truss had to occur within tightly coordinated track outages and navigation channel closures.
• Seismic Retrofitting of River Piers: To meet updated safety standards for seismic activity and vessel collisions, we strengthened the four existing river piers by encasing them in new concrete and micropiles. This retrofit ensured the piers met Level-2 seismic standards and enhanced their ability to withstand impacts from vessels.
• East Approach Improvements: The east approach, consisting of 31 multi-beam spans from the 1890s and six deck plate girder spans constructed in 2006, was also retrofitted. We encased the steel trestles with lightweight cellular concrete and used MSE walls to contain the new fill. We improved the deck structure by shifting to a ballasted deck system, which replaced the open-deck structure. This improvement widened the track centers and increased overall stability.
• Environmental Services and Permitting: The project required extensive environmental clearance documentation and approvals. Our team facilitated coordination between federal agencies, including the Federal Railroad Administration (FRA), U.S. Coast Guard (USCG), U.S. Army Corps of Engineers (USACE), and FEMA, as well as bi-state coordination with Missouri and Illinois state agencies. Our team obtained the necessary permits and provided compliance support throughout the construction process.