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
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
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
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
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.