Rehabilitating an Historic Landmark
Spanning the Mississippi River in downtown Minneapolis, Minnesota, the 140-year-old Stone Arch Bridge is a former railroad bridge crossing recognized as a National Civil Engineering Landmark. In the early 1990s, the Minnesota Department of Transportation (MnDOT) converted the 2,100-foot-long masonry bridge into a pedestrian and bicycle pathway. To ensure public safety and cultural value of the bridge, MnDOT hired Collins Engineers to assess and restore the structural integrity of the bridge. Given the age and size of the structure, Collins faced challenges when developing repair plans that traditional data collection methods could not accommodate.
Digitalizing Inspection and Design
To identify structural deficiencies and develop repair plans, Collins needed detailed information on the condition of masonry for the entire bridge, including stone arches, embankments, piers, and underwater foundations. Conventional workflows would be time consuming, significantly impact public use of the bridge, and might not produce the level of detail required to generate accurate repair plans. While Collins used reality modeling technology on previous projects, they realized that for this large and complex structure, they needed an integrated digital survey, modeling, and inspection solution to collect sufficiently detailed data to accurately model the bridge.
Leveraging a Mixed Reality Environment
Collins selected ContextCapture to generate a high-fidelity 3D model as the basis of a digital twin of the Stone Arch Bridge from over 13,000 drone captured images. Using Bentley’s reality modeling and digital twin applications, they performed virtual inspections and established a mixed reality environment for the team and public to view the digital twin of the bridge and gain a better understanding of the restorative design works. Traditionally, inspection notes were recorded and communicated using pencil and paper, accompanied by photos, that lacked the necessary detail to make definitive decisions and safely complete the project. However, working with the 3D digital twin meant the field team could inspect the bridge remotely, record their findings directly on it, and accurately pinpoint the areas in need of repair.
Digital Twins Drive Lifecycle Benefits
Using advanced digital technologies to survey the bridge allowed Collins to shorten the time that the bridge was out of service during inspection, limiting pathway closure to just four days. Working in a mixed reality environment using an accurate digital twin of the bridge, they saved 20% in field time and improved the quality and quantity of data collected, facilitating more informed decision-making to reduce risk and cost. The digital twin will enable contractors to deliver more competitive bids, which is expected to save MnDOT 10% to 15% in construction costs. Collins will extend the use of digital twins beyond design and construction for future lifecycle planning and maintenance, ensuring that the bridge continues to remain structurally safe and a valuable cultural asset to the city and state.
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Content produced in association with Bentley Systems