Research Problem and Background
The aging civil infrastructure across the United States has been under the spot light due to recent bridge failures such as the I-35W bridge collapse. Many concrete and steel bridges that were built in the mid 20th century in response to the boom of automobiles are reaching their life expectancy, leaving questions about their structural integrity and deterioration levels. Millions of dollars have been invested each year to inspect bridge components using various technologies such as ground penetrating radar (GPR), seismic pavement analyzer (PSA). These equipments are normally large and carried by trucks to monitor the health of the steel reinforced concrete bridge decks. However, for some difficult to access components (e.g., bridge foundations and pillars underneath decks), it lacks effective tools for regular inspection. Figure 1 shows a common method of under bridge inspection using snooper truck by a 2-man evaluation team with handheld non-destructive evaluation (NDE) devices. Among the available NDE devices, handheld impact-echo (IE) is the most commonly used technology for evaluating concrete and masonry structures.
The current practice of manual inspection has to block traffic, and is time-consuming, expensive, and exposes human workers to dangerous situations. We propose to develop an automatic impact-echo system on board a specially designed wall-climbing robot to automate the inspection process. Compared with manual inspection, the wall-climbing robot will be able to scan vertical surfaces of bridge foundations and horizontal surfaces at the bottom of bridge decks, reach hard-to-access places, take close-up pictures, record and send impact-echo data wirelessly to host computer, and log GPS coordinates at every test point in a software system for further analysis. A group of such wall-climbing robots can do the inspection task simultaneously, making the automated inspection faster and more thorough than manual inspection, thus saving time and money, making the national civic infrastructure more secure.
Research Objectives
The objectives of the project are three folds:
1) To custom design a wall-climbing robot system with a safety mechanism and power/signal tether for bridge inspection. The robot will have enough payload to carry a camera and an impact-echo device. The robot will be able to operate on vertical surfaces of bridge foundations and on horizontal surfaces at the bottom of bridge decks, commanded by a human operator using a remote controller.
2) To develop and evaluate an automatic impact-echo system and integrate it with the wall-climbing robot. Based on an existing hand-held impact-echo device, the system will add new features for automatic inspection. A new impactor will be designed using solenoid as the actuation source to achieve 2D scanning measurement at multiple points in a line with adjustable distance between transducer and impactor. Acoustic filtering algorithms will be designed to reduce noise from background and robot propeller. In-house evaluation of the impact-echo system will be conducted on a test-bed by the civil engineering team in collaboration with the electrical engineering team.
3) To conduct field test of the integrated robotic inspection system with on-board camera and automatic impact-echo device for visual inspection of cracks as well as detection of delaminations, voids and other defects that are beneath the subsurface.