Remote Sensing Data For Bridge Preservation Decision Making

Presenting and storing bridge inspection data in an evocative manner plays an important role in decision making procedure of transportation authorities. Currently the method of storing this information in Michigan is aligned to the MDOT (Michigan Department of Transportation) inspection methods, which includes visual inspection of bridge and storage of NBI (National bridge Inventory) reports on a specific database. 3D optics and Thermal Infrared (IR) imagery are two innovative technologies that have the potential to not only improve the current methods of inspection practice, but also to help bridge inspectors have their bridge inspection data for future reference, preservation and decision making.

3D optics is a photogrammetric technology that can create a stereographic map of the deck surface condition by taking images with sixty percent longitudinal overlap. This technology can help in detecting spalls and scaling on the bridge by creating a Digital Elevation Model (DEM) of the bridge deck surface and storing this information in Geographic Information System (GIS). Thermal IR imagery is a technology based on measuring radiant temperature of the concrete bridge deck and can help bridge inspectors to locate delaminations and calculate the overall delaminated area on the bridge. Total area of spalls and delaminations will indicate the deficiency of bridge deck.

This product presents concrete bridge deck inspection data collected by 3D optics and thermal IR technologies. Freer Rd. Bridge near Chelsea, Michigan was the case study for this presentation. According to the last inspection report of this bridge (June 2010), the overall NBI rating of the deck condition was 6 (0-9 NBI rating). In the image submitted, the three outputs are arranged for a side by side comparison. Digital images of the concrete deck surface were taken with certain overlap to allow for creating the elevation model of the surface by using SLR digital camera. The DEM shows the amount of deviation of the bridge deck from an artificial plane. This plane was set as the base elevation of the deck itself and shows that the elevation of the bridge deck varies about 22cm. This DEM could also be use to locate spalls and to calculate  spalled area and volume estimates. With a resolution of 5mm in the x,y direction and about 4mm in z, this DEM allows bridge inspectors to produce highly accurate and detailed assessments. Also, these digital images were used to create an orthographic image of the concrete deck. This image will give an overall overview of the whole bridge deck condition as well as help in interpreting the thermal IR images. These images were taken after delamination survey was done by bridge inspectors using hammer sound technique and markings on the bridge deck indicate the results of this survey. Thermal IR images were collected on the bridge deck and a deck delamination map was created from these images. Both thermal IR and 3D optic data were added to the GIS environment to represent the total area of deck deficiency.

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