Advanced Infrastructure Systems Laboratory

Evaluation of Modular and Mobile Robotic Systems for Civil Infrastructure Inspection and Maintenance Tasks

State departments of transportation cite structure condition as a critical transportation problem. A major contributing factor to structure condition is insufficient and deferred maintenance. Although several factors are significant contributors to deterioration of structure condition, the only factor that engineers have complete control over is timely preventative maintenance.

Timely inspections are needed, and must be designed to be thorough enough to identify potential problems before they become significant maintenance and repair items, or safety concerns. For instance, in many bridges, multiple structural elements are critical to the safety of the structure. Most of these elements are hidden, and visual inspection is complicated. Furthermore, current protocol for inspection of bridges calls for a two-year inspection cycle. Currently, the federal department of transportation (DOT) recommends that the biannual inspection be supplemented by a program in each individual district that would identify the preventive maintenance needs of a structure on an annual basis. Given the number of bridges, many local and county governments are unable to complete detailed yearly inspections with the available number of inspectors and engineers. The problem is significant in the state of Pennsylvania, where a large number of bridges are closed on an average day due to maintenance or repair work [3]. Furthermore, rigging and traffic control consumes 40-50% of the total inspection/repair cost, not considering the cost due to traffic back logs [1].

For yearly inspections, bridge decks, which consume a large part of the maintenance budget, deck joint systems, drainage systems, bridge bearings and end structures, which are usually very hard to reach, need to be checked. Several maintenance tasks also must be performed. Visible corrosion of exposed steel members, accumulation of debris, cracks on the deck, and the condition of deck drainage systems, bridge bearings, seats, and caps as well as many other points must be identified and documented frequently. Besides requiring many man-hours, such tasks are frequently dangerous and force the closing of one or more lanes on the highway.

A similar problem related to inspection of large civil structures is encountered in large warehouses, parking lots and airstrips. To assess the cracks and laminations on the surface, engineers currently employ inspection methods that require a group of individuals to visually inspect the surface and mark the significant defects on their notepads. These notes are later combined with CAD/CAE application software to obtain a global picture of conditions. The process requires multiple engineers to survey the site. Furthermore, the manual visual inspection of the site requires the engineers to locate their position exactly in order to obtain a realistic data. Although the procedure can be carried out by trained individuals, the task is repetitive, time consuming and requires precise position information about the location of the surface markings on individual notebooks.

The surfaces to be inspected in a civil structure can be vertical as well as horizontal. An example is the inspection of tall buildings as opposed to bridge surfaces. The procedure for inspection of vertical surfaces is slightly more difficult. In addition to the problems mentioned above, the inspector needs to be lowered along side the surface to be inspected. The scaffolding or rigging mechanism used by the inspectors must be capable of moving sideways as well as horizontally.

Other inspection tasks that requires the inspectors to be in high-risk situations while entering difficult areas while tethered onto a safely line (under a bridge deck, inside water and sever mains, on the facades of the buildings, in small-diameter wells, or limited access pipelines).

Visual inspection of civil structures is not limited to flat surfaces, bridge decks and truss members. Inspection of different kinds of pipe and duct systems is another problem facing civil engineers. Pipelines are used in the industry for transporting oil, gas, and water, and for many other applications. There are a wide variety of pipelines and ducts used in urban settings for distribution of the gas, water, electricity and data as well as collection systems (e.g., sewage). These structures are indispensable in our daily life, and are prone to failure due to high temperature, high pressure, internal friction, clogging, material buildup and other environmental factors. The second leading cause of pipeline failure in the US is corrosion, which is caused by the contact of metal pipe with wet soil (external corrosion) and with the fluid in the pipe if the fluid is corrosive or contains water with dissolved oxygen, carbon dioxide, or hydrogen sulfide (internal corrosion). Damage to anyone of the pipelines or duct systems mentioned above could be financially and environmentally costly.

However, these systems are particularly difficult to inspect and repair due to their location (buried underground), size (anywhere from 3m to 20cm), and shape and structures (e.g., elbows, branches, valves, or vertical pipelines). The total length of a pipeline system to be inspected is another factor that renders the inspection task almost impossible. For example, in Germany, ten percent of the 360,000km public sewage system needs to be inspected every year. On the other hand, driven by an unprecedented demand for energy, oil pipeline construction increased. Growth in pipeline construction was modest (up 8% in 1997) with a total of 30,250km. One-third of all the new projects in 1998 were in the U.S. This comes to approximately 10,000km new pipeline every year in U.S. during the last few years.

The delay in inspection cycles or lack of periodic inspections causes many problems in civil infrastructures. Most of the bridge closings due to extensive repair can be prevented with timely inspections. In many cases, a timely inspection would stop detoriation before costly and sometimes irreversible damage is done to the structure. During 1999, there were multiple instances of structural failure in U.S. (See [4,5,6,7] for recent examples).

The inspection tasks listed above have to be carried out periodically for a large number of structures. Many large structural systems require continuous inspection, since by the time the inspection is completed the next cycle of periodic inspections starts. Furthermore, as mentioned above, these tasks involve high-risk situations for operators/surveyors/inspectors. In many of these situations, humans don’t perform well due to safety concerns and physical limitations. Also, repetitive tasks that require precise positioning and visual inspections are not suitable for humans.

We believe that many of these inspection tasks are suitable for mobile and modular robotic systems specifically designed for the tasks in question. The results of employing robots will have positive effects on:

• time-to-completion of a given inspection task, and percentage of the structures inspected in a given cycle [faster/parallel evaluation due to multiple, more capable robots]

• correctness of the gathered data [less error; mathematical error models are not possible in the case of  human inspection teams]

• completeness of the data [more coverage]

• costs indirectly related to the inspection task [road closings, costs incurred by failures due to delayed inspection]

• life threatening situations [humans not involved directly with inspection tasks]

Next section describes our initial plan for developing robotic inspection systems for some of the tasks described above.

  Approach:

A detailed list of the inspection and maintenance tasks mentioned in the previous section includes the following:

·        Inspection of bridges (decks, trusses and girders)

·        Inspection of large warehouses, parking lots and garages, air strips

·        Inspection of exterior walls of tall buildings

·        Inspection of pipes and ducts

·        Painting and/or paint removal for above structures

·        Space applications

Mobile (wheeled or treaded) robots and modular robotic systems are two candidate approaches for mobility of the inspection system. Robotic vision and sonar sensing are the obvious and commonly used candidates for the actual inspection. This section briefly introduces our approach associated with these methods, related technologies and state-of-the-art.

Other approaches for inspection of civil structures include serpentine robots for bridge inspections [1], mobile snake-like robots for inpipe inspections [6, 7, 8], other mechanisms for suspended cables [9] and mobile manipulators capable of walking over extensive space solar power stations [2].

Investigators:

• Mark E. Patton, Department of Civil and Environmental Engineering, CIT, co-PI 

• Cem Ünsal, Robotics Institute and Institute for Complex Engineered Systems, co-PI

Project Duration and Cost:

• November 1999-December 2000.

• $29,881.

Project Affiliation:

• AIS Laboratory, ICES, CMU
  Jim Garrett, Prof., CEE

• Pennsylvania Infrastructure Technology Alliance (PITA)
  Georgette Demes, PITA Associate Director, ICES