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Publication Number: FHWA-HRT-06-072
Date: March 2006

Multiyear Plan for Bridge and Tunnel Security Research, Development, and Deployment

Section 5: Proposed FHWA Multiyear Program

FHWA envisions a multiyear program that addresses securing the existing infrastructure and that will lead to the next generation of bridges and structures that are resilient to this new threat.

Terrorist threats to bridges can include:

  • Fire (can lead to buckling of steel beams and spalling of concrete).
  • Impact (can lead to damage of piers, causing collapse of the superstructure, and failure of hangers, again resulting in collapse of the superstructure).
  • Mechanical cutting devices (can lead to cutting of hangers, resulting in collapse of the superstructure).
  • Corrosive chemicals.
  • Blast or explosion (can lead to severe damage of the structure).

Terrorist threats to tunnels can include:

  • Fire.
  • Impact.
  • Chemical/biological attack.
  • Blast/explosion.

While we need to design for all threats, bombs constitute 60 percent of terrorist attacks worldwide.

Strategic Focus Areas

The proposed FHWA program focuses on the following strategic areas to reduce the threat of damage to the infrastructure so that there is minimal loss of life, the infrastructure can stay open for movement of people and goods, and there will be little or no impact on the economy.

The recommended strategic focus areas for bridge and tunnel security R&D include:

  • Risk and Vulnerability Assessment.
  • System Analysis and Design.
  • Improved Materials.
  • Prevention, Detection, and Surveillance.
  • Post-Event Assessment.
  • Repair and Restoration.
  • Evaluation and Training.

Research Program Goals

The following identifies the major goals for each of the seven strategic focus areas given above.

Risk and Vulnerability Assessment

Goal: Develop better decision support tools, and more relevant and uniform methodologies for assessing the risk to and vulnerability of the highway infrastructure.

System Analysis and Design

Goal: Develop new analysis and design methodologies for highway bridges and tunnels to minimize physical damage.

Improved Materials

Goal: Explore and develop new materials, and improve on current materials for the next generation of bridges and tunnels.

Prevention, Detection, and Surveillance

Goal: Adapt existing technologies and develop new technologies for better detection and surveillance and prevention of terrorist incidents.

Post-Event Assessment

Goal: Develop guidelines for assessing the safety of structures after an event.

Repair and Restoration

Goal: Develop better repair and restoration techniques to restore a structure to its original capacity.

Evaluation and Training

Goal: Test and evaluate new technologies, and develop training aids to transfer new technologies.

Tie-in to the National Critical Infrastructure Protection R&D Plan

Table 1 shows the relationship between the NCIP R&D theme areas and FHWA strategic focus areas. One of the goals of both plans is to have "resilient, self-diagnosing, and self-healing physical (and cyber) infrastructure systems."

Table 1: Relationship between NCIP R&D theme areas and FHWA strategic focus areas.

NCIP R&D Theme Areas

FHWA Plan: Strategic Focus Areas

Risk and vulnerability assessment

System analysis and design

Improved materials

Prevention, detection and surveillance

Post-event assessment

Rapid repair and restoration

Evaluation and training

Detection and sensor systems






Protection and prevention







Entry and access portals


Insider threats


Analysis and decision support systems





Response, recovery, and reconstitution





New and emerging threats and vulnerabilities




Advanced infrastructure architectures and systems design







Human and social issues


Research and Development Recommendations

Based on analysis of the outreach efforts, the following R&D priorities were developed. This list should be revisited annually to ensure its continuing relevance and to update as necessary.

The studies that have been or are close to being initiated by FHWA and others are italicized in table 2 and in the study descriptions that follow.

Table 2: Research Studies

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Table 2: Research Studies Continued

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Table 2: Research Studies Continued

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A short narrative is given below for most of these initiatives.

Risk and Vulnerability Assessment

Goal: Develop better decision support tools and more relevant methodologies for risk and vulnerability assessment.

Synthesis of existing risk and vulnerability assessment methodologies: This project would have a multi-hazard approach. There is a need to develop consistency in the levels of risks used in design to safeguard structures from both natural and terrorist attacks. Designers apply different return intervals for various aspects of design, which may or may not relate to a consistent risk analysis. For flooding, roadways are allowed to overtop at return intervals anywhere from 10 to 50 years, depending on the class of road. For seismic hazards, a 2500-year event is often selected for retrofit designs. For wind hazards, a 20-year occurrence event is selected for construction, a 100-year event is used for strength, a 1000-year event is used for flutter during construction, and a 10,000-year event is used for flutter of the completed bridge. Currently, there is no basis for designing for security in the design codes and standards. A synthesis is needed to clarify the state of the practice and to determine the feasibility of reaching a consistent set of guidelines for evaluating risks and cost benefits for all hazards. This study would conduct a literature search and synthesize all available risk and vulnerability assessment methodologies for extreme events, including floods, wind events, earthquakes, blasts, overloads, and accidents (collisions, fires, etc.), and develop and recommend a framework for a consistent methodology for all extreme events. The literature search would also look at probability methods, such as those used in industrial reliability. The resulting document and recommended framework will be used by FHWA for developing a single risk and vulnerability methodology for all extreme events encountered by the Nation's highway bridges and tunnels.

Determination of levels of risk and probability of occurrence for each event, and development of consistent risk assessment methodology: This project would conduct a broad investigation and identify acceptable risk levels in designing for each hazard type and the basis for their use. It would identify recurrence interval or probability of occurrence for each extreme event for each risk level. It would study the patterns of recurrence and how well each method has worked, as well as the economic costs incurred after using the method. The extent of loss of life would also be researched. The project would recommend if a single set of consistent levels of risk for all hazards is feasible. This study would start with analyzing results from separate analyses of individual hazards, selecting the level most likely to be satisfactory, and then comparing the projected effects of the new design events to those in use to determine if safety and cost are increased or reduced. Finally, this study would develop a risk assessment methodology utilizing the framework developed in the previous study.

Development of criticality models for bridges and tunnels for incorporation into risk assessment models:This study will add to the developed risk assessment methodology by providing criticality models for different events for each risk category.

Lessons learned - Bridge demolition:This study would gather pertinent information from demolition companies on demolitions of structures in order to learn from their experiences. The goal would be to learn the difficulty and ease of the job; explosives needed (how much, what type, shape and location of placement; analytical approaches used; software type; time on target required, etc.).

Guide to risk management of multimodal transportation infrastructure (NCHRP): This National Cooperative Highway Research Program (NCHRP) study is developing a guide that will provide State DOTs and other transportation entities with a risk management methodology that can be used to conduct threat, vulnerability, and criticality assessments of their facilities and to determine cost-effective countermeasures to prevent, detect, and reduce threats to assets on a multimodal basis. The product of this project will be a recommended replacement to the 2002 AASHTO Guide to Highway Vulnerability Assessment for Critical Identification and Protection.

System Analysis and Design

Goal: Develop new analysis and design methodologies for highway bridges and tunnels to minimize physical damage.

Assessment of bridge designs for structural vulnerability against terrorist events: The goal of this project would be to investigate and identify key components of each bridge design type for vulnerability to blast loadings, fire, and intentional impact. A summary of activities may involve collecting common bridge designs from State highway agencies, such as the designs of representative I-girder, box girder, suspension, cable-stayed, curved girder, and slab-type bridges; categorizing hazard loadings into different levels or classes; reviewing and assessing each bridge design type subjected to the different levels or classes of hazard loadings; identifying vulnerable details; and recommending design solutions and/or vulnerable elements requiring further study. This study would also look at where information exits, past performances of bridges during these events. This may include gaining access to infrastructure performance from the military from bombings in wars, military combat demolition, and military research. Although the types of ammunition used by the terrorists would most likely not be as sophisticated, much can be learned about the vulnerability of bridges from this available data. The expected products would be a document identifying vulnerable details and recommended solutions for each bridge design type and recommendations for future work. This study would be followed by subsequent studies to develop optimized designs and countermeasures for mitigating and hardening structures for extreme events.

Assessment of tunnel designs to resist blast and fire:This project would parallel the above project, but would concentrate on tunnels. The goal would be to investigate and identify key components of tunnel design for vulnerability to blast and fire. Activities may involve collecting tunnel design types, including soil conditions; categorizing hazard loadings into different levels or classes of loadings; review and analysis of each design type, subjecting each to the different levels or classes of hazard loadings; determining the weaknesses of each type; and recommending design solutions. This study would also look at, where information exits, past performances of tunnels during these events. This may include gaining access to the military on performance of tunnels from bombings in wars, military combat demolition, and military research. Although the types of ammunition used by the terrorists would most likely not be as sophisticated, much can be learned about the vulnerability of tunnels from this available data. The expected products would be a document identifying vulnerable details, recommended solutions for each tunnel design type, and recommendations for future work.

Making transportation tunnels safe and secure (NCHRP): The objective of this NCHRP research study is to develop safety and security guidelines for owners and operators of transportation tunnels to use to identify: (1) critical locations; (2) potential structural improvements; (3) operational countermeasures; and (4) deployable, integrated systems for command, control, communications, and information. The guidelines are to be applicable across the spectrum of both accidental and intentional threats.

Optimized designs for hazard loadings:This would involve multiple studies to develop design solutions for vulnerable designs, details, or weaknesses identified in the previous studies. It involves tailoring vulnerable details of structures for mitigating the consequences of a blast, utilizing improved fire-resistant materials and designs, and designing solutions for resisting vehicle and vessel collisions for vulnerable structures.

Catalog of optimized design solutions for each event:This project would compile into one document all optimized design solutions for each extreme event. It would be a "how to design for ..." manual with illustrations and information on what and what not to do for the bridge designer.

Advanced physical and numerical modeling and simulation capabilities for predicting and understanding behavior under extreme events:This study would develop analytical capabilities to be used for predicting the behavior of structures under extreme events. The product would be of use to researchers, code developers, and bridge designers for making decisions in lieu of experimental tests.

Blast-resistant designs - Impact attenuators - Structural cladding:Following the Oklahoma City bombing, the General Services Administration (GSA) developed a series of bomb-blast requirements for buildings. For example, the Federal Aviation Administration's Eastern Regional Headquarters building in Queens, NY, utilizes precast panels that meet the GSA's requirements. Basically, it is a self-supporting building structure built within a self-supporting facade. The walls provide the blast-zone loading with the concrete and steel reinforcing stressed within the elastic range. These walls are the primary protective elements that provide resistance in case of an explosion and are considered "hardened elements." The cladding used outside these walls consists of precast concrete architectural panels with laid-up brick. The facade is only nominally supported by the concrete frame. They designed a bunker-type structure, but clad it with precast concrete and brick in such a way that it absorbs the initial force of a blast. There is a 101.6-millimeter (4-inch) gap between the building's architectural features and structural elements. The goal of the precast concrete is not to be protective to an exterior explosion, but to "peel away" in case of a bomb blast, providing protection and absorbing force. It takes the first hit and absorbs some of the force, minimizing damage that could be caused by collapsing. The backup concrete wall then takes most of the force. The precast concrete serves as a "crumple zone" to protect the rest of the structure.

A study should be conducted to determine the feasibility of using this or similar design concepts for critical components of bridges and tunnels, such as piers, pylons, towers, tunnel walls, etc. Using this concept, one could make the cladding sacrificial and save the structure. If determined to be feasible, second and subsequent phases could be initiated to develop the concept further and to test on actual bridge and tunnel critical components.

Blast-resistant highway bridges: Design and detailing guidelines: This NCHRP study involves developing guidelines for selecting analysis techniques and developing design and detailing guidelines, evaluating approaches to enhancing the performance of bridges subjected to blast loads, and developing guide specifications and a procedure for assessing bridge damage caused by explosions.

Structural vulnerability guide:Currently, there are no guidelines, specifications, tools, or experience to determine the structural vulnerability of infrastructure (bridges and tunnels) to terrorism. The AASHTO Guide to Highway Vulnerability Assessment deals more with susceptibility to an attack based on location and the importance of the structure. The FHWA/U.S. Army COE's Bridge and Tunnel Vulnerability Workshop deals with structural vulnerability in an attack because of blast loadings, irrespective of the location. The material for the workshop is based on the U.S. Army COE's experience with infrastructure research to support the military's objectives. According to the U.S. Army COE, little or no research has been done in the specific area of terrorist threats against bridges and tunnels. Numerous Federal Agencies conduct R&D on security measures against hostile attacks. R&D in related areas, particularly protection against natural disasters and accidents, may also be effective in preventing the destruction of structures from hostile attacks. This project would explore these areas to determine applicability to highway structures and to develop a structural vulnerability guide.

Blast effects and retrofit techniques for tunnels:Research to determine blast effects and to develop retrofit techniques may be needed for some tunnel types, especially those on soft or poor soils, underwater, and cut and cover tunnels. There may also be a need to look at improving ventilation systems, designing systems for mass evacuations, etc. Based on what was presented at the U.S. Army COE's Bridge and Tunnel Vulnerability Workshop, numerous explosive tests have been conducted for the military on tunnel design systems anticipated by the military. Almost all of these, however, have been on one-way tunnels (i.e., there is only one entrance in and out of the tunnel). These tunnels are used to store ammunition and as shelters, not for moving people. Some of these tunnels also have berms in front of the entrances, which can mitigate the blast energy. As such, the current research data possibly would not be applicable to vehicular tunnels. If an explosive is detonated in a vehicular tunnel, the blast energy has clear exits in two directions; therefore, the reflection waves might even be less. This project would determine the blast effects on vehicular tunnels and develop retrofit techniques through analysis and testing.

Standardized blast response curves for bridges: This study is developing simple design aids to help engineers design bridges for blast loadings. The study will produce a standardized set of blast response curves for a generic set of common bridge elements, including decks exposed to deck-top detonations, steel and prestressed girders exposed to deck-top detonations, rectangular and wall-type piers exposed to side-on detonations, and a single-cell tower of a cable-stayed bridge exposed to side-on deck-level detonations.

Bridge-specific blast loading program: This study is developing a user-friendly computer program for consistent definition of blast loadings on bridges. The U.S. Army COE's current computer program, ConWep (Conventional Weapons Effects), is widely used within the engineering community to predict blast loadings on structures from conventional weapons, including terrorist-type vehicular bombs. This program was originally developed as an expedient and user-friendly tool for engineers concerned mostly with building structures. The graphical user interface (GUI) of this program will be modified to better facilitate bridge-specific problems. It will develop a user-friendly and bridge-specific GUI for reliable definition of key parameters such as weapon size, weapon standoff, weapon orientation in relation to the structural element, the overall size of the structure, and the size of the responding element of interest.

Validation of numerical modeling and analysis of steel bridge towers subjected to blast loadings: Most major long-span bridges in the United States are vulnerable to terrorism. They are high-visibility structures, with a potential for extensive media exposure and public reaction if an incident were to occur. As a result of the long spans, complicated designs, site locations, etc., these bridges have very high replacement costs and multiyear replacement construction periods. The potential for impacting regional and national economies is also greater because of the increased time for reconstruction. Many of these bridges serve as transportation arteries critical for emergency evacuation and for carrying lifelines besides vehicular traffic. This study will develop several numerical models and analysis validated through the construction of physical models subjected to large explosive devices detonated to determine the actual behavior of such towers. This study will further develop and test several hardening concepts for cellular steel bridge towers so that the performance of these towers can be well understood in the event of such an attack occurring after the hardening has been implemented.

Blast testing of full-scale, precast, prestressed concrete girder bridges: This study will: (1) assess the damage done to precast, prestressed girder bridges from a blast generated below the girders, (2) compare this damage with a blast generated on top of the bridge deck, and (3) develop recommendations for possible mitigation measures that would harden this type of bridge blast damage. Precast, prestressed concrete girder bridges are the most prevalent bridge design in the country.

Material Performance

Goal: Explore and develop new materials, and improve on current materials for the next generation of bridges and tunnels.

Response modification devices: This projects aims to develop and refine response modification devices such as dampers, isolation bearings, yielding devices, and shape-memory alloys. This project would also look into developing cladding systems that take the initial impact and thereby lessen the load on the main members. The project would take a multi-hazard approach in developing devices for hazard mitigation.

Material performance under extreme event loadings: The behavior of construction materials in bridges subjected to fire is a critical issue that has not been addressed adequately in the past. The behavior of new high-performance materials is even less understood, and the enhanced material characteristics may be even less suited for high-intensity fires, such as a burning tanker truck carrying liquid petroleum. Although accidents involving trucks carrying hazardous materials are a common occurrence, the risk is amplified as a result of terrorism. As a first step toward developing fire-resistant construction materials and protective coatings, the performance of both normal-strength and high-performance steel and concrete during a fire needs to be assessed. This study should lead to a better understanding of the performance of materials during explosive loadings and fires. The study would include materials such as normal-strength and high-performance steel and concrete. It would determine how much blast material (energy) and heat are needed to damage a structure constructed of these materials so that the structure is no longer functional. This information could be used to determine design loads and also design mitigation measures. If the load required to damage a structure is unreasonable, this would also let you know that nothing needs to be done.

Resistant materials and coatings for improved performance: This study aims to develop materials and coating systems that can be applied to highway structures that can resist high-intensity fires and absorb blast loadings.

Shape-memory alloys for bridge structural applications: Shape-memory alloys are metallic composite materials capable of changing shape and returning to their original form after stresses have been removed. These materials have been in existence for more than 30 years. Structures made of these materials hold promise for possessing energy-absorbing capabilities, enabling them to sustain high-velocity impacts or explosions. The materials hold promise for resisting seismic, blast, and high-impact loadings. Although some research is being conducted, most is concentrated on the seismic issue. This study would assess these alloys for mitigating terrorist-type loadings.

Nanoscale science and engineering research: Nanoscale science and engineering represents an opportunity to engineer materials/devices with novel characteristics. At approximately 1 to 100 nanometers (a nanometer is equal to one-billionth of a meter), clusters of atoms and molecules exhibit properties very different from those found at larger scales. Nanoscience is the creation of new materials, devices, and systems at the molecular level. It can significantly improve mechanical, optical, chemical, and electrical properties. Through nanoscience, it is possible to create ductile ceramics. Nanoscience materials enable radical design changes. The National Nanotechnology Initiative is a White House initiative involving 10 agencies. TFHRC, through its Advanced Research Program, has a number of research studies in this area. The possibility of protecting structures against terrorist threats through the use of nanotechnology by providing new designs, new materials, and blast-resistant structures is a new area that should be explored. This would be long-range, high-risk research with the potential for a high payoff.

Nanoscience research areas include:

  • Materials that perform well under extreme conditions of temperature and pressure. These can be strong, tough, ductile, lightweight, and low-failure materials.
  • Smart materials such as paints that change color with temperature.
  • Radiation-tolerant materials.
  • Self-healing materials: Research is ongoing at the National Aeronautics and Space Administration's Langley Research Center on self-healing materials development to develop materials that will mend themselves if subjected to high-velocity projectile penetration. This technology has the potential for structural applications in bridges. Nanoscale self-healing materials can be developed to be embedded in structural materials that become activated at the site of a fracture, etc., and self-heal the material.

Nanotechnology can be used to build stronger, lighter, and harder materials as has already been done in the aerospace industry.

MEMS sensors research: Research into micro-electro-mechanical systems (MEMS) would be another high-risk, high-payoff research. Its application in structures can include structural monitoring and structural control, nondestructive evaluation, and materials engineering and analysis. MEMS sensors can be used to measure physical properties (temperature, pressure, strain, magnetism, etc.) and inertial properties (vibration, tilt, acceleration, and velocity); for chemical and particle detection, and range and motion detection; and for imaging. Examples of these sensors include silicon accelerometer, silicon gyro, micro-hotplate chemical sensors, and ion-mobility spectrometer and pressure sensors.

MEM sensors can be used to design for security. They are already a key element in improving the performance of concrete. Cyberliths are complete monitoring and telemetry systems on a chip that can be embedded in artificial pebbles and thrown in with the aggregates during the mixing of concrete. More sophisticated cyberliths could be developed to measure stress distributions. MEM methods have been applied to manufacture thousands of miniature ultrasonic transducers on a single chip. It is more powerful than conventional transducers and enables inspection by noncontact, nondestructive technology. MEM actuators can be used at selected locations to control structural vibrations. Nanosensors embedded in cables, piers, pylons, and decks could sense imminent danger or collapse and alert engineers. Nanosensors embedded at various locations on a structure could act as the "brain" of the bridge and alert authorities to multiple hazards.

Prevention, Monitoring, Detection, and Surveillance

Goal: Adapt existing technologies and develop new technologies for better monitoring, detection, surveillance, and prevention of incidents, catastrophic failures, and/or condition assessment.

Synthesis of bridge surveillance and security techniques: This study is synthesizing the state-of-the-art practices related to surveillance and security of our bridge structures, and developing an evaluation framework to select among alternative surveillance and security approaches.

Hazard mitigation measures: This project would include studies to develop countermeasures for mitigating hazards. It would include blast mitigations systems and impact absorption devices.

Sensing and monitoring technologies for extreme events:This project would develop sensing and monitoring technologies that can be incorporated into our bridges and structures to monitor performance during extreme events, detect intruders, and help assess the post-event capacity of structures. It would include developing monitoring and warning devices to prevent vehicle collisions on bridge girders and vessel collisions at bridge piers. It would also include developing monitoring and warning devices to predict bridge scour, movement of bridge piers, and aerodynamic instability.

Post-Event Assessment

Goal: Develop guidelines and methodologies for assessing the safety of structures after an event.

Forensic analysis of damaged structures to understand residual capacity and develop protocols for rapid assessment: The ultimate goal of this project would be to develop an inspection protocol/checklist to be followed in assessing structural safety, which can be done rapidly in times of crisis. The first step might be to compile a report or synthesis of "bridge morphology." This should be a complete listing of all bridge failures, collapses, and demolition. The purpose is to obtain a broad view of what can happen to a bridge. The next study would expand our interest to include major damage to bridges. After determining the most likely incidents, conduct an analytical and experimental study of damaged structures to determine their remaining capacity and to understand how and why the damage occurred. The study will require a literature search of the subject and an exhaustive study of reports on past damaging events. Then it will be necessary to develop analytical and laboratory models of the damaged parts of the structures for further testing. It may also be possible to obtain portions of old or damaged bridges for the laboratory tests. Once the testing is done, develop new protocols for assessing damage and remaining strength.

Inspection techniques for rapid safety assessment of damaged structures:In times of crisis, being able to rapidly determine the residual strength of structural members is crucial. This study would develop nondestructive evaluation techniques/capabilities to assist the structural engineer in determining the residual capacity of damaged structures.

Damage assessment guide for extreme events: This study would produce a field guide based on the results of previous studies for the assessment of structures for damage from extreme event loadings. It would develop guidance on emergency stabilization analysis; failure investigation; material strength evaluation; and determination of which areas are safe and which areas need to be demolished, and which methods should be used for demolition.

Repair and Restoration

Goal: Develop better repair and restoration techniques to restore a structure to its original capacity.

Emergency repair procedures:Studies on this will require an idea of the types and levels of damage that are expected. This would have to be done as part of system analysis and design, probably as a study (or studies) under assessment of current bridge and tunnel designs for structural vulnerability to multiple hazards. There would be studies to determine the damage expected under various single hazards. The next step would be to predict the damage caused by two or more simultaneous events. This information could be used as a starting point in identifying and/or developing emergency repair procedures. Once we know the nature of the damage to be expected, repairs can be developed. As a start, this would involve shoring, temporary spans, precast or prefabricated members, and also repairs to damaged members that have retained considerable strength and are salvageable. The study should also find other ways to repair or replace damaged members and keep traffic flowing. Maintenance and protection of traffic should be an integral part of these studies.

Accelerated repair and restoration techniques for reconstruction after an event:These studies will complement and flesh out the emergency repair procedures covered above. Accelerated methods are a must for emergency repair procedures. In fact, except for routine maintenance, most repair procedures should be accelerated since they usually interfere with traffic or are executed under difficult physical conditions. Application and monitoring of innovative concepts for repair or replacement complete this study. Considering the demands in terms of working rapidly and fixing weakened members, developing and deploying innovative procedures is another must.


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