The Federal Highway Administration (FHWA) is proposing a robust and aggressive research and technology (R&T) program to preserve the aging and deteriorating U.S. bridge infrastructure and advance new technologies for designing stronger, longer-lasting bridges. This program would build on and expand the programs pursued under the Transportation Equity Act for the 21st Century (TEA-21) and previous FHWA R&T programs. The first in a three-part series, this article describes FHWA's proposed strategy for inventorying and preserving the current stock of bridges in the U.S.
The most extensive transportation network in history--including highways unparalleled in the world for quality and capacity--ties our nation together. The U.S. highway system connects people to jobs, hospitals, places of worship, cultural and sporting events, national parks and family members across the country. Roads play a vital role in the country's economic development, emergency response during natural and man-made disasters and national defense, linking manufacturers to retailers, farms to markets, military installations to deployment stations and shippers to seaports, airports and railroads.
Bridges are critical elements in that network. They provide safe passage over railroads, waterways and topographic features. They facilitate grade separations and interchanges that ensure safe and efficient handling of high traffic volumes. FHWA is committed to delivering a cost-effective bridge infrastructure to meet America's present and future needs. FHWA is working to minimize or eliminate deficiencies in bridges that contribute to congestion, hamper mobility or represent safety concerns.
To meet the demands for a 21st century transportation network, FHWA is proposing a comprehensive program of bridge research and technology. Unofficially termed Bridges for the 21st Century, the program will result in cutting-edge solutions to the problems of the nation's aging and deteriorating bridge infrastructure.
"FHWA, in partnership with the states, will be developing and deploying innovative technologies," said Raymond McCormick, acting director of FHWA's Office of Bridge Technology, "that enable us to get out ahead of the bridge deterioration curve and stay there."
Specific research needs
Future stewardship and preservation of the bridge infrastructure will require new research and technology, as well as innovative tools, strategies and management practices. The four cornerstones of the Bridges for the 21st Century program are accurate and factual information, trained and motivated people, innovative and cost-effective technology and deployment of proven, innovative technologies. To achieve a solid foundation for the program, the necessary research, development and technology deployment will involve several diverse but complementary disciplines, including corrosion engineering, material sciences, nondestructive testing, management sciences, economics and bridge design and construction. Each of these disciplines plays a critical role in the ability of highway agencies to manage and preserve the physical bridge infrastructure.
Breakthrough developments will be necessary in a number of research areas. One need is to understand and define the micro- and macro-level processes and mechanisms that result in the physical deterioration of bridge materials and elements and limit the useful life of bridges. For example, a better understanding of the role of alkali-silica reactivity in concrete deterioration is necessary to develop cost-effective prevention and mitigation technologies.
Improvements also are needed in the technology for inspecting and quantifying the condition of bridges and bridge elements, including nondestructive testing, remote sensing techniques and global monitoring. For example, techniques and systems for scour detection and monitoring substructure movement in real-time are necessary to minimize damage and protect the safety of traffic on bridges.
Materials and methods are needed to counter or mitigate the impact of deterioration processes in new structures, structural elements and existing bridge members. One example is highly corrosion-resistant reinforcing materials that significantly delay the onset of corrosion, then corrode more slowly, delay structural damage or are easily repaired and greatly increase the useful life of concrete bridge decks.
Breakthroughs are needed in technology for the rapid repair and rehabilitation of bridges to minimize the duration and public disruption of work zones, such as congestion and safety for the public and highway workers. For example, prefabricated, lightweight bridge elements, such as decks of fiber-reinforced polymer composite, can be installed in days instead of weeks.
Improvements should be made in the quality, accuracy and precision of quantitative information on bridge conditions, such as element-level data that support improved processes and tools for decision making regarding bridge management. Research could include technologies for detecting the condition of bridge decks at highway speeds and methodologies to assess the condition of concrete decks with overlays.
Finally, improved modeling for life-cycle cost analyses could lead to cost-effective strategies and techniques for preventive maintenance that extend and optimize service life.
Three thrusts of the R&T program
To meet these and other bridge research and technology needs, FHWA has envisioned and proposed the Bridges for the 21st Century program as part of the surface transportation legislation that will authorize highway and bridge programs for fiscal years 2004 through 2009.
The program will have three major thrusts. The first--the focus of this article--centers on stewardship and management of the existing bridge inventory to ensure safe, continuing service at the lowest cost.
The second thrust centers on ensuring the safety and reliability of bridges by eliminating or minimizing the impacts of natural hazards like floods and earthquakes. Another aspect of this focus is minimizing the damage from man-made stresses, such as overloads, vessel or vehicular impact or intentional damage from terrorist activities.
The third thrust involves developing a new generation of cost-effective, high-performance and low-maintenance bridges. FHWA envisions a new paradigm in design and construction that results in bridges that are built faster and cheaper, with a minimum 100-year life span, and require little or no maintenance. In part, this thrust would build on the results of the Innovative Bridge Research and Construction program in TEA-21.
Over the next several decades, newer bridges will replace many of the spans that today still provide service on U.S. highways. In the interim, it is critical that bridge owners develop and implement innovative, cost-effective ways of preserving the existing inventory.
Data maintained by FHWA in the National Bridge Inventory show that the nation's public highways include more than 480,000 bridges and 110,000 tunnels and culverts. The total deck area of just the bridges with a clear span of more than 20 ft in length adds up to more than 3.2 billion sq ft. An equivalent two-lane bridge with this deck area would stretch almost 17,000 miles.
The bridge infrastructure in the U.S. is aging and deteriorating. The mean age of all bridges in the U.S. is 42 years and rising. Bridges deteriorate, or in a more general sense, become deficient, for many reasons. For example, in many parts of the country, the need to clear roads of snow and ice quickly and thoroughly results in frequent applications of deicing salts, which lead to corrosion of metal components like bearings, rebar and steel floor beams or girders.
Marine and industrial environments also drive corrosion of reinforcing steels and steel prestressing strands, damaging concrete bridge members, reducing load capacity and compromising safety. Bridge owners need to be able to determine the causes of these failures, analyze the effects of various mitigation technologies and then implement the most cost-effective solutions.
Even without significant physical degradation, bridges become deficient over time because the geometrics and the load capacity of the as-built structures make them inadequate for growing traffic volumes and loadings. Inspectors classify a bridge as deficient when the deck, superstructure or substructure receives a rating condition of "poor" or worse. Culverts, 20 ft wide and larger, which are classified as bridges for inspection purposes, also are considered deficient upon earning a rating of "poor" or worse. Bridges also qualify as deficient if they are assigned an appraisal rating of "low" for structural evaluation, waterway adequacy, deck geometry, under-clearance or approach alignment.
Focus on preservation
In the past, many bridge owners neglected bridges until they were beyond rehabilitation and in need of replacement. One primary objective of FHWA's stewardship and management focus is to encourage bridge owners to provide more emphasis on system preservation based on state-of-the-art preventive maintenance and rehabilitation techniques.
In step with the new emphasis of its proposed bridge program, FHWA encourages state and local highway agencies to use state-of-the-art preventive maintenance technologies that control deterioration; employ innovative and cost-effective repair, strengthening and rehabilitation technologies as alternatives to bridge replacement; and develop comprehensive and relevant measures of the performance of highway structures.
All aspects of stewardship and management rely heavily on sound, quantitative data on bridge conditions and comprehensive information that documents the factors that influence performance and deterioration. Currently that type and level of information is either not available in a format useful for analysis or not available at all.
A primary component of FHWA's Bridges for the 21st Century program is a proposed Long-Term Bridge Performance program that would provide the data to support improved tools, methods and programs for bridge preservation and management. The 10- to 20-year program would monitor 1,000-2,000 carefully selected bridges representing a cross section of the infrastructure.
Each bridge would be instrumented and monitored to collect research-quality data on the most important factors that influence deterioration and affect performance.
This type of quantitative data, collected for thousands of bridges over 10-20 years and properly analyzed, would lead to significant advancements in the knowledge of bridge performance.
These studies would help researchers better understand causes of deterioration and develop and deploy proven preventive maintenance and rehabilitation techniques. Researchers also could improve models for assessing future deterioration and deficiencies, so transportation agencies could develop and implement cost-effective strategies for bridge preservation.
The need for innovative technologies for bridges is critical and urgent, as agencies work to extend the life of the existing bridge infrastructure at the lowest cost. FHWA's Bridges for the 21st Century program, including the proposed Long-Term Bridge Performance program, would fill a critical need for reliable data on bridge conditions and performance and greatly enhance the results of bridge management systems.
The next installments in this series describe FHWA's goals of developing new materials and technologies that will maximize bridge life with little or no maintenance and generating designs and strategies for mitigating the damage of extreme events such as earthquakes, flooding, vessel or vehicle impacts and terrorist attacks.