Big City, Bigger Infrastructure Challenges
By Raimondo Betti
From the Fall 2012 special issue of Columbia Engineering Magazine
There is no doubt that the infrastructure of current and future large cities is a critical issue in our society. The importance of infrastructure to both the fabric of society and its economy is nowhere more apparent than in our urban centers. Its fragility as it ages is exemplified by incidents like the recent collapse of the I-35W Bridge in Minneapolis, but the problems are generally pervasive and less evident.
One key problem: money. Budgets set aside for infrastructure maintenance and monitoring are slim, but the costs tied to them, steep. Public (federal and state) expenditures on infrastructure grew slowly (1.7 percent per year) from 1956 to 2004, and slightly more (just 2.1 percent) in recent years. The American Society of Civil Engineers (ASCE) estimates that upgrading the nation’s infrastructure system will cost $2.2 trillion over a five-year period. The Federal Highway Administration reports that the costs resulting from the loss of a critical bridge or tunnel could exceed $10 billion. ASCE estimates that Americans spend $54 billion each year on vehicle damage repairs caused by poor road conditions. Our water systems are also failing. According to the Environmental Protection Agency (EPA), there are 240,000 water main breaks per year in the nation with an estimated waste of some six billion gallons of drinking water each day.
The crucial role of infrastructure as an indicator of the health of a society was eloquently described by the Civil Infrastructure System Task Group of the National Science Foundation in its 1993 report: “The rise and fall of a civilization ultimately is linked to its ability to feed and shelter its people and to defend itself. These capabilities depend on the vitality of its infrastructure—the underlying, nearly imperceptible foundation of a society’s wealth and quality of life. A civilization that stops investing in its infrastructure takes the first step toward decline.” Today this call to action is even timelier, and advanced sensing technologies, whether for roads, highways, bridges, or water systems, are providing us with a new and improved way of addressing this need.
Increasingly, the infrastructure of the future is being envisioned as having the ability to monitor its own health through a complex network of sensors that, in real time, will be able to provide an estimate of its structural integrity and, if necessary, activate corrective actions. For example, modern bridges are built with a sensor network that can reach up to 10,000 sensors, monitoring, in real time, accelerations, deformations, tilting, temperature, wind speed, humidity levels, etc. This new trend is especially applicable and needed for aging infrastructure for which continuous monitoring becomes essential for safe operation. In other engineering fields—mechanical, aerospace, and electrical engineering—such diagnostic philosophy is common, but only recently has it found consideration in civil infrastructure applications. There are similarities with other applications to be copied here, but there are also many profound differences and challenges as well that must be addressed.
About the author
A key area of the research thrusts in structural monitoring will be a thorough investigation of different types of sensors for a variety of infrastructure applications (e.g., flow meters to detect leaks and blockages in pipelines or motion sensors for structural integrity of bridges and buildings). Of course, existing sensor technologies where appropriate will have first consideration, but where needed, development of new sensors need to be pursued.
For example, a monitoring system for main cables of suspension bridges, developed at Columbia University, integrates many types of sensors for corrosion, temperature, pH, and other characteristics needed to assess the condition and remaining strength of main cables which, to date, are not readily inspected. Some of these sensors already have successful records in other applications but are not necessarily transferrable to suspension bridges.
The cross-disciplinary character of sensor development and handling the large amounts of data are ideally suited to the broad-based data center focused on Smart Cities that the Engineering School intends to create. Expeditious collection and processing of the large amounts of data requires new methods of communication that will also be a subject of research. Instead of installing a new communication infrastructure, the infrastructure itself will be used to transfer information. We will investigate ad hoc wireless networks, communications over the power network, and intermittently connected networking techniques.
Since in large urban areas there will be large numbers of sensors connected in complex networks, special attention will be given to networking techniques that process sensor readings during collection to reduce the required bandwidth. In addition, the power requirements for monitoring widely in transportation, water distribution, and sewer systems of large urban areas can be mitigated by focusing on use of low bandwidth communications to perform infrequent “meter reading” or to summon an intermittently connected networking collection device (with mobile radio and storage nodes for water and sewer lines or with passing trains in the subway system).
The use of sensor information in assessment methodologies to evaluate the structural health of the aging infrastructure system, even when the information is less than complete for the numerical models of the specific system, will enable quick response reactions in keeping with the management models that will be developed.
Our Civil Engineering and Engineering Mechanics (CEEM) Department is uniquely positioned in the area of Structural Health Monitoring (SHM). Keeping its strength on the mechanics end of the spectrum, the CEEM Department has created a group in SHM comprised of leading experts in research areas critical to our goal of remedying aging infrastructures. My own research and that of Professor Andrew Smyth focuses on structural health monitoring and damage assessment of different structural systems, such as bridges and buildings, while Professor George Deodatis brings to the group his expertise on uncertainty quantification. Professor Maria Feng is working on the development of innovative technologies for novel fiber optic and vision-based sensors as well as on microwave imaging technology. Professor Richard Longman, a world-renowned expert in control theory, complements the CEEM SHM team with his work on vibrationbased system identification.
This strong SHM group will continue to concentrate its research initiatives, critical to our goal of remedying aging infrastructures, in the areas of evaluation of existing sensor technologies and development of new sensors; collection, processing, and communication of large amounts of data; data and sensor fusion; power requirements for large sensor networks; data interpretation and system identification; structural health monitoring and damage assessment of different infrastructure evaluation types (e.g., bridges, buildings, pipelines, etc.); and quick response assessment.
As part of the Institute’s program, we will be training a new generation of civil engineers in both the use of such tools and the development of new ones to ensure that our infrastructure, and our civilization, continues to advance.