Currently, visual inspections and the limited deployment of nondestructive technologies are the primary tools for post-hazard bridge inspections. Researchers conducted an engineering post-hazard assessment of bridges and investigated the use of technologies for assessment through field tests conducted in September 2017. Field tests used Unmanned Aerial Systems (UAS) for three-dimensional (3D) photogrammetry of two bridge structures in Maryland and Unmanned Water Systems (UWS), consisting of a remote-controlled sonar boat, for developing bathymetric profiles. Sensor technologies included a single-beam sonar mounted on UWS and high-resolution optical imagery from UAS. In addition, an investigation on the resolution of bridge movement detection was conducted using UAS through testing of a scaled bridge model.
- Assess post-hazard structural stability from UAS measurements. High-resolution imagery and video collected by UAS can be used to evaluate the debris field and create models. The overall position and condition of bridge elements can be assessed and compared to the bridge plans to determine the amount of change that the elements have experienced.
- Use a multi-source dataset from UAS and UWS for hydraulic modeling. Processed bathymetry data collected by an unmanned surface vehicle, when combined with bathymetry data and terrestrial elevation data from other sources, can be used as input for 2D and 3D hydraulic modeling.
- Use UWS to detect scour holes. UWS can be used to collect bathymetry data around bridge piers in a relatively short amount of time. Processed data can be used to identify potential clear-water scour holes near bridge piers and abutments, although detecting live-load scour can be more challenging. This type of data collection and processing can be used to periodically assess scour holes and help inspectors determine how scour is progressing.
- Assess the stability of scour countermeasures using UAS. UAS can be used to collect high-resolution images above the water, supplemented with sonar for underwater data. By processing the imagery into a 3D model, quantitative measurements and positional information can be obtained.
- Capture bridge movements on an actual bridge in service. The focal length and sensor size, together giving the range of view, are important in photogrammetric processing. Therefore, full-scale bridge testing can be followed up with a field scenario measuring the likely movement of bridge elements. Existing bridge features can be used as markers, and the availability or unavailability of baseline data or as-built plans can help inform the use of the sub-centimeter technology capabilities.
- Utilize state-of-the-art UAS with higher resolution cameras for the assessment of the structural integrity of bridges. These cameras can be used to determine the appropriate hardware needed for the sub-centimeter resolutions necessary for the assessment of bridge integrity. This could also lead to a standard equipment configuration that other state agencies could adopt for post-hazard preparedness.
- Leverage 3D photogrammetry images for development of crack detection algorithms. Crack detection algorithms from 3D photogrammetry images could be utilized at bridges damaged from hydraulic or other hazards such as vehicular impacts.
- Consider using UAS to assess an array of bridge problems. UAS can be used to assess an array of problems including the cracking of deck, column or girder elements, movement of bearing pads, damage or fracture of anchor bolts, column failure modes, girder bending or shear damage, rotation of deck, and ground spreading due to liquefaction.