Simple bridge security inspection : final report, September 2006

An important aspect of designing bridges for security in an economically feasible way is to have in place plans for evaluating the criticality of any one structure on the transportation network. Thus, in deciding how to allocate resources, bridges considered more essential to the transportation infrastructure, or those thought to be at higher risk for a terrorist attack, should be given priority in the implementation of protective measures over other less critical bridges. This paper describes methods of carrying out threat and vulnerability analyses and risk assessments. Once the risks to a given bridge have been assessed, measures may need to be taken to mitigate these risks if they are deemed unacceptable. These measures generally attempt to prevent an attack by increasing surveillance or limiting access, but they can also include actions to limit the effects of blast loads or procedures to aid in rescue and recovery. Usually, deterrence and prevention measures will provide the least expensive solution to mitigate risk initially. Therefore, a risk manager should consider implementing these measures for short-term risks before strengthening a structure is specified. Deterrence and prevention, however, may not always provide the most costeffective solution for long-term risks when considering life time costs, such as maintenance, replacement, personnel, and inspection costs.

2006

There are some similarities between seismic and blast effects on bridge structures: both major earthquakes and terrorist attacks/accidental explosions are rare events that can induce large inelastic deformations in the key structural components of bridges. Since many bridges are (or will be) located in areas of moderate or high seismic activity, and because many bridges are potential terrorist targets, there is a need to develop structural systems capable of performing equally well under both events. This paper presents the findings of research to establish a multi-hazard bridge pier concept capable of providing an adequate level of protection against collapse under both seismic and blast loading, and whose members’ dimensions are not very different from those currently found in typical highway bridges. A series of experiments on 1/4 scale multi-hazard bridge piers was performed. Piers were concrete-filled steel tube columns (CFST columns) with different diameters (D = 4”, 5” and 6”...

SAFE …, 2005

It is undeniable that the security environment in the United States has changed. Acts of terrorism in the U.S. and across the globe have warranted that particular attention be paid to the vulnerability of civil infrastructure in this new environment. As a result, it is important that planners and administrators are able to evaluate risks to infrastructure in their jurisdiction in a rational manner. This will enable them to take optimal actions to manage these risks given budgetary constraints. This paper develops a method for quantifying the vulnerability of infrastructure to attack and for examining the magnitude of consequences of such an attack. It includes consideration of uncertainty in the magnitude and type of initiating events. Structural reliability principles are used to ascertain the probabilistic nature of damage to a structure given the random initiating events. Consequences of infrastructure damage are considered in terms of various costs. A case study involving a fictionalized cable stayed bridge is illustrated in this paper.

Bridge Structures, 2008

Structural health monitoring (SHM) is becoming increasingly popular with bridge owners and administrators for bridge evaluation and management. At the same time, bridge security is also emerging as an important consideration for all infrastructure owners. But the role of SHM for bridge security aspects is not well understood or studied. A workshop was held with representative members of bridge owners, researchers, consultants, and security personnel to evaluate several aspects of this issue. This paper summarises these deliberations, subsequent data analysis, and pertinent results associated with various SHM technologies, measurement methods, and interaction between stakeholders. These results will be helpful to the SHM and security communities in understanding the role of SHM in enhancing bridge security.

Structure and Infrastructure Engineering, 2008

Blast mitigation research on a series of bridge components to date has shown both similarities and differences between seismic events and explosive loads in terms of structural response. Similarities on the load side include the fact that both blast and earthquake loads are largely unknown in terms of location, magnitude, intensity, type, etc., and both have characteristics of rapid attenuation with distance from the source mechanism. In terms of consequences, both actions can result in progressive structural collapse, requiring redundant structural systems for mitigation. Significant differences in these two extreme event scenarios also exist; these include load duration and associated strain rate effects and the extent of initial damage or excitation. The similarities and differences between blast and seismic hazards and their responses are explored in a series of blast mitigation field tests, laboratory tests, and computational analyses to form the basis for multi-hazard mitigation in bridge structures.

WIT Transactions on State of the Art in Science and Engineering, 2012

The design of bridges to resist blast loads has become an international concern in recent years. Data from the U.S. State Department indicate that violent attacks against transportation targets have increased worldwide over the last decade and that highway infrastructure has been the most frequently attacked transportation target. Since September 11 th , 2001, increased emphasis on bridge security has raised awareness in the engineering community that bridges and other transportation structures should be designed to better respond to potential terrorist attacks. The fact that many bridges provide open access, carry thousands of motorists, and may have symbolic importance makes them attractive targets, and the success of recent terrorist bombings on bridges during the ongoing "war on terror" highlight the vulnerability of these structures. This paper presents preliminary results and observations from blast tests on concrete bridge columns conducted during a U.S. national study to develop design and detail guidelines for blast-resistant highway bridges.

2012

U.S. engineers need advanced tools and protocols to better assess and assure safety and serviceability of bridges. The Federal Highway Administration, American Association of State Highway and Transportation Officials, and National Cooperative Highway Research Program sponsored a scanning study of Europe to identify best practices and processes to assure bridge safety and serviceability. The scan team found that the European highway agencies expect their bridge programs to not only ensure user safety, but also to meet serviceability expectations and enhance capital investment decisions. The team gathered information on safety and serviceability practices and technologies related to design, construction, and operations. Team recommendations for U.S. implementation include developing a national strategy to increase use of refined analysis for bridge design and evaluation, encouraging States to use refined analysis combined with reliability analysis to avoid unnecessary rehabilitation or replacement of bridges, and encouraging adoption of the concept of annual probability of failure to quantify safety in probability-based design and rating specifications.

Structures Congress 2014, 2014

Cable stayed bridges provide an efficient structural solution over a wide range of span lengths and as a structural form, are often used to build an iconic structure. Protecting them from threats, both malicious and accidental, presents a number of challenges. This paper presents a number of different mitigation decisions made as a consequence of Accident Threat and Vulnerability Assessment (ATVA), sometimes known as Risk and Vulnerability Assessment (RVA), in the design development of four cable stayed bridges currently under design or construction in the US, and for which the authors have knowledge of the design. Details about each bridge are provided for the purposes of comparison and are limited so as to maintain the confidentiality of the threat and vulnerability assessment of the specific bridges discussed. Key considerations discussed for the bridges include: (1) Main tower protection, (2) Deck stability, (3) Loss of cables, and (4) Fire protection.

1997

The authors suggest that the work required to strengthen sub-standard bridges needs to be prioritised taking into account costs and risks to the public. A framework is proposed for a risk-based approach for assessment of bridges and simplified methods for risk evaluation. The procedure is most appropriate for bridges which do not satisfy the requirements of a standard assessment of load carrying capacity using current assessment codes. The method is part of an ongoing research project intended to be dovetailed into the strategic research programme being conducted by the Highways Agency. The prupose of the proposed methodology will be to identify the low risk bridges for which traffic disruptive interim measures may not be necessary and to select appropriate remedial actions. For the covering abstract see IRRD 898092.

2011

: This report presents the results of the initial phase of a research study with the objective of documenting the current state-of-the-practice, at the national level and for the 32 states and the Commonwealth of Puerto Rico having military installations, related to the requirements, selection criteria, and inspection process for bridge safety barriers. The focus of the study was directed at identifying policies and recommended practices related to low speed, low volume road environments. This report includes basic policies and guidelines from pertinent Federal Highway Administration (FHWA) and American Association of State Highway and Transportation Officials (AASHTO) documents that deal with aspects of roadway geometric design, roadside design, and safety barrier practices and their relation to bridge safety. Information is included about FHWA-approved crashworthy bridge railing systems used by some states. State-specific tables that summarize the relevant information about the re...