• Harper Leavitt Engineering

    Decommissioning and Replacement of 1930s Del Rio Bridge on US 20

    St. Anthony, Idaho, United States

Project Summary


Harper Leavitt Engineering was contracted to provide construction engineering on site for the relocation and later removal of an existing steel truss bridge originally constructed in the 1930s, as well as to facilitate the erection of a pre-cast concrete replacement bridge on the existing alignment, all with minimum disruption to the local environment and on a tight schedule. Over the years, the cross girders had sustained damage from increasing high load traffic which was becoming more frequent, and could eventually make the existing structure unsafe for use.  


The design team had to find the most economic and efficient solution to install 140,000-pound concrete girders on a 150-foot span between two piers across a river without employing the biggest mobile cranes, as they were too costly. Taking an innovative approach, they decided to use the existing bridge frame as a temporary support structure for installing the new girders. In turn, the new bridge, once built, could be used to remove the original steel frame off site for dismantling, while protecting the environment.


The design team was able to proceed with its innovative, lower-cost solution with confidence, using STAAD.Pro for analysis. As a result, the city of St. Anthony has a newly-constructed bridge more suited to the changing demands of its lumber industry, which uses large, modern trucks with high loads.


The Harper Leavitt team used STAAD.Pro to analyze and confirm the viability of their proposed solution to use a bridge in a way that was never envisioned when originally constructed – as a temporary support structure. Bentley’s LEAP software (for the design of piers and for checking continuous prestressed girders) and MicroStation (to detail plans and render 3D drawings) were also used in the design and detailing.

  • The innovative approach reduced crane fees by approximately 50 percent and minimized the time the bridge was closed. This, in turn, reduced the amount of time local traffic needed to use the detour.
  • The design and approach developed by the design team enabled the rapid construction of the bridge. The project was completed on time.
  • “I have used STAAD.Pro for 20+ years and use it for all my complex structural analysis. In a 'can-do will-do' world, I rely on technology like this to meet my customers' demands. I can rapidly produce safe and efficient designs and share the results with my customers with confidence for use in their projects.”

    Robert B. Butler Principle Engineer Harper Leavitt Engineering