ABSTRACT
The world invests about US $1,430 billion annually in the construction of structures, including: buildings (residential, commercial, industrial, etc.), civil works, and utilities, such as highways, water and sewer structures, railroads, and transmission lines. Construction is the largest industry in the world amounting to 10% of the world's gross domestic product. Structures are generally the most expensive investments/assets in any country. In addition Note: Part of this paper is taken from "Overview of Nondestructive Evaluation Projects and Initiative at NSF" by K. P. Chong, J. B. Scalzi and O. W. Dillon in Intel1iaent Structures. Elsevier, London, 1990. *to present paper
structures have long service life compared with any other kinds of commercial product, and are rarely replaceable once they are erected. Yet the feedback and controls on the "state of health" of structures are practically non-existent (compared with say the much less costly automobiles). Nondestructive evaluation is an essential part of this feedback and monitoring system for infrastructures. During the past several years, many reports have been published concerning the sad state of deterioration of the nation's public works, such as bridges, roadways, water and sewer systems, ports, harbors, airports, and buildings of all types. According to the 1988 National Research Council Report on "Building for Tomorrow" estimates of public infrastructure amounted to $409 trillion in 1984, and growing rapidly. The U.S. Interstate System, built in the 1950's needs repair, so do most of the state and county secondary roads. Some 42% of all U.S. highway bridges are inadequate and half of school buildings are 50 years or older. In the U. S. alone, recent bridge collapses include: o Mianus River Bridge - Connecticut, 1986, 3 deaths o Schoharie Creek - New York, 1987, 10 deaths o Hatchie River - Tennessee, 1989, 8 deaths o Miamis Town River - Ohio, 1989, 2 deaths According to David Aschauer (Chief Economist of U.S. Federal Reserve Bank - Chicago), a 1% increase in public capital causes 1/3% rise in productivity. From 1971 to 1985 U.S. productivity growth fell 1.2%, out of which 1% was attributed to neglect of the infrastructure. If the present infrastructure deterioration continues, the Department of Transportation estimates that the U.S. economy will miss out on: o 3.2% growth in GNP o 5.9% disposable income o 2.2% employment o 2.7% productivity
The infrastructure ages and deteriorates with time. The deterioration is mostly a result of aging of the materials, excessive use, overloading, climatic conditions, lack of sufficient maintenance, and difficulties encountered in proper inspection methods. All of these factors contribute to the obsolescence of the structural system as a whole. As a result, repair, retrofit, rehabilitation, and replacement become necessary to insure the safety of the public.
