A New System for Preventing Bridge Collapses
Of these, combined and consequent events are the most likely multihazard events except for scour, which can cause long-term subsequent events. In practice, it may be difficult to distinguish between combined and consequent events. The critical lesson is that bridge design and planning must increasingly take into account such combinations of events.
Bridge experts are becoming aware that bridges should be situated, designed, retrofitted, and maintained with a view to an ever-widening range of extreme loads and their combinations, with terrorism posing a new challenge. It is appropriate that, as the field of engineering progresses, its practitioners should refine their work to improve quality, cost-effectiveness, and public safety. If the United States is going to increase investment in infrastructure, it is essential that it have reliable information on what makes bridges safer.
We can make progress in bridge safety by modeling the reliability relationship between loads (including multihazard loads) and resistance and by developing improved structural modeling and materials. Both kinds of progress depend on better data, but obtaining better information is no easy task.
For building or bridge design (as compared to the design of ordinary commercial products), it is prohibitively expensive to put the structure through destructive testing. The National Science Foundation does establish facilities for earthquake study, with shake tables where experimental structures can be tested, but this testing is necessarily conducted on models that are far smaller than the structures of interest. It is also desirable to conduct research during the demolition of an obsolescent or otherwise unneeded bridge, but such research is almost unheard of in the United States, perhaps because of legal constraints.
Additional results may be obtained from forensic engineering studies of failed bridges. A well-developed approach is the post-disaster reconnaissance study, in which teams of engineers and other investigators examine the unique confluence of events that caused a structural failure. But such failures are rare and highly varied in the combinations of hazard types, severities, structure types, soils, and chains of causation that they exemplify. The studies simply do not provide enough evidence to enable generalizations about hazard effects. In addition, the fundamental flaw of forensic studies is that they take place only after a bridge has failed.
We believe that an especially useful supplemental source of information will be incident reporting. Its essential and distinctive feature is this: Reporting is on all incidents, including near-misses, minor mishaps, and significantly stressful events, not just spectacular accidents, disasters, or failures.
With respect to bridges, the challenge would be to measure and document events that severely stress a bridge but result in little or no damage. Data should be collected and coded in a rigorous, consistent manner. The data should encompass both the loads (and the single or multiple hazards that caused them) and the structural impacts. When such incidents, as well as full-fledged accidents are studied, the resulting database may be large enough to allow for statistical analysis. A practical advantage is that the organizations involved are more willing to share information about small incidents than major ones, where issues of liability and official responsibility arise.
Incident reporting systems are now required for airplane accidents and near-misses and are routinely recommended for the study of medical errors and construction site incidents. To implement such a system for bridges, the United States should develop and widely implement a structural health monitoring system on bridges. Such a system will track stresses, strains, and other conditions on the structure and its components and will identify, locate, and measure the effect. Such systems could have added value beyond data collection—for example, for real-time emergency management or to inform bridge operators of conditions during and after extreme events.
This system should also unify forms and reporting that are now collected in many different ways. At present, hazard data are sought by specialists in meteorology, hydraulics, seismology, highway accidents, fires, maritime accidents, volcanology, hazmat events, and security threats. Coordinated and consistent data collection is essential because even measures of severity are difficult to compare across hazard types. Fire intensity, for example, is not quantifiable in the same way as flow velocity or buoyant uplift from flooding.
Of course, it makes sense that data must be defined and screened by the pertinent scientific disciplines. However, excessively uncoordinated data collection and inconsistent reporting serve as an obstacle to policy insight on the probabilities of harm to various infrastructures and on ways of alleviating this harm.
In view of the resurgent concern about bridge safety, we propose infrastructure incident reporting through a National Bridge Health Monitoring System. To the extent that it focuses only on bridges, the system should be implemented under the auspices of the Federal Highway Administration, in cooperation with disaster preparedness agencies such as the Federal Emergency Management Agency and its state counterparts, state highway departments, and universities. Implementation should follow experimental testing by means of small-scale pilot projects in selected states. Should the tests prove successful, the system should be expanded to the United States as a whole.
While collecting data on structural damage, engineering researchers also must systematically develop damage models, so as to be able to predict failure processes for various kinds of structures and materials under extreme events. For long-term improvements in bridge safety, observations from destructive testing, forensic studies, reconnaissance studies, and bridge-health monitoring have to be integrated in predictive analytic models.
With such improvements, U.S. infrastructure investment would be more cost-effective on a risk-adjusted basis, because bridge decisionmakers would have more accurately accounted for the range of hazards and multihazard effects to which bridges are susceptible. In addition, although such a project may be initially developed for bridge safety, U.S. infrastructure as a whole would derive economies of scope from extending the system to meet broader needs for national protection.
Blue Ribbon Panel on Bridge and Tunnel Security, Recommendations on Bridge and Tunnel Security (Washington, D.C.: Federal Highway Administration, 2003).
R. Necati Catbas, Melih Susoy, and Naim Kapucu, “”Structural Health Monitoring of Bridges for Improving Transportation Security,” Journal of Homeland Security and Emergency Management 3, no. 3 (2006): article 13.
David L. Cooke and Thomasa R. Rohleder, “Learning from Incidents: From Normal Accidents to High Reliability,” System Dynamics Review 22, no. 3 (Fall 2006): 213–239.
M. Ghosn, F. Moses, and J. Wang, Design of Highway Bridges for Extreme Events [Washington, D.C.: National Cooperative Highway Research Program (NCHRP) Report 489, Transportation Research Board, 2003].
NCHRP, National Needs Assessment for Ensuring Transportation Infrastructure Security: Preliminary Estimate [Washington, D.C.: NCHRP Project 20-59(5), March 2003].
National Institute of Standards and Technology (NIST), Performance of Physical Structures in Hurricane Katrina and Hurricane Rita: A Reconnaissance Report (Gaithersburg, MD: NIST, Technical Report 1476, June 2006).
Ilyas Ortega, “The Incident Reporting System (IRS),” Quality Management and Technology Report Series, Report No. 8 (St. Gallen, Switzerland: University of St. Gallen, December 1999), 1–10.
Ernest Sternberg, and George C. Lee, “Meeting the Challenge of Facility Protection for Homeland Security,” Journal of Homeland Security and Emergency Management 3, no. 1 (2006). Available at www.bepress.com/jhsem/vol3/iss1/11.
Alistair Sutcliffe, “Scenario-Based Requirements Engineering,” Proceedings of the 11th IEEE International Conference on Requirements Engineering (2003).
K. Wardhana and F. C. Hadipriono, “Analysis of Recent Bridge Failures in the United States,” Journal of Performance of Constructed Facilities 17, no. 3 (2003): 144–150.
George C. Lee ([email protected]) is Samuel P. Capen Professor of Engineering and Ernest Sternberg ([email protected]) is a professor in the Department of Urban and Regional Planning at the University at Buffalo of the State University of New York.