US-31 Bascule Bridge Survey

Spalding DeDecker (SD) provided the Michigan Department of Transportation (MDOT) with a complete 360° point cloud As-built Design Survey of the US-31 Manistee Bascule Bridge. SD used four LiDAR scanners to scan 4 gears, treads, tracks, and other vital components to collect three-dimensional data. SD was responsible for scheduling and directing all aspects of scanning, including coordinating with the bridge operator, data processing, and performing quality control and quality assurance checks on the extracted data. Additionally, SD scanned the underside of bridge assist with bridge inspection, repairs, and for future reference.

The Challenge
This type of project warrants a tight design tolerance, a high level of safety precautions, and extreme diligence with safety standards. Since the bridge was open to roadway and water traffic, SD had to create a site-specific work plan to ensure the safety of its field personnel and the equipment capturing the essential data.

The Solution
SD scanned the gears and corresponding tread tracks in order to design new castings for the drawbridge. SD scanned the gears in three phases; down, open to tread, and fully open to tread. Since the bridge was open to traffic, an 8-minute window was provided to capture data at each phase. SD repeated
the process four times, creating 16 registrations and capturing the details of moving parts in multiple positions. Measuring moving objects adds complexity, especially when the required measurements for the matching replacements tracks are unyielding. The castings will be used to make new components that will accurately replace the old mechanisms without having to do a complete reconstruction.

The Impact
Using LiDAR technology allowed SD to be very efficient and safely acquire the data with minimal interruptions. The use of scanning and workflow development has set a precedent for utilizing scanning for bridge rehabilitation projects. Spalding DeDecker proved that alternative methods can be utilized to aid the design process and prolong the life span of the existing bridges.