Acceptable Risk in Military Bridge Evaluation

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.

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...

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.

2009

Performance of the transportation network strongly depends on the performance of bridges. Bridges constitute a vital part of the transportation infrastructure system and they are vulnerable to extreme events such as natural disasters (i.e., hurricanes, earthquakes, floods, major storms), as well as hazards stemming from negligence and improper maintenance, collisions (vessels and vehicles), intentional acts of vandalism, and terrorist attacks. These structures must be protected but the current approach to risk is not rational. Therefore, the objective of this project is to develop efficient risk analysis procedures for assessment of the actual safety reserve in highway and railway bridges. The focus is on the approach at the system level using system reliability methods. Sensitivity analysis relates the reliability of bridges and of the transportation network. The results will then be used to identify the critical parameters. The target risk will be determined depending on consequences of failure and relative costs. Rational selection criteria will be developed for the target risk level for bridges (components and systems) as a part of the transportation network, based on the consequences of failure and relative costs. This will involve the development of efficient system reliability procedures that will be applied to perform sensitivity analysis relating various parameters and reliability. The resulting sensitivity functions will provide a rational basis for identification of the most important parameters that affect the network performance. Rational selection criteria for the target risk will find important applications in decision making processes regarding operation, maintenance, repair, rehabilitation and replacement. This proposal will impact education and development of human resources since it will provide undergraduate and graduate students with research opportunities. The results will be included in courses and will be disseminated to wider audiences through presentations and publications.

Proceeding of the 33rd European Safety and Reliability Conference

A periodically unattended bridge is a likely use case, often cited with regards to Maritime Autonomous Surface Ship (MASS) technologies. The German-funded B ZERO project aims to develop and demonstrate capabilities which are needed for navigating a cargo ship for up to 8 hours within a predefined operational envelope. From a risk perspective, MASS technology, and thus the implementation of B ZERO must be as safe as conventional technology, which is why a safety assessment of the B ZERO concept is executed according to the International Maritime Organization Formal Safety Assessment guidelines. This paper outlines the results from the hazard identification and risk analysis executed along the Bow-Tie Model. The risk analysis focuses on quantitative methods such as Fault and Event Tree Analysis Modeling, for relative comparison of conventional (attended) bridge and unattended bridge instead of qualitative expert-based ratings in risk matrices. It includes insights into how risks associated with MASS can be modeled by identifying reasonable probabilities from literature.

IABSE Conference, Seoul 2020: Risk Intelligence of Infrastructures

Risk management plays a crucial role in the stakeholders’ decision making because it is directly related to safety, serviceability and economy. There is now a growing concern about how to relocate known risks into an acceptance threshold: this implies the evaluation of several options obtained from hazard scenarios considering the related consequences. In parallel, practitioners usually rely on standard tools for risk assessment, and on structural codes to compute performances. Although this approach is currently widely implemented, this research shows that hazardous situations can arise in properly designed infrastructures, due to errors in management. This paper deals with such issue, also highlighting a gap in current codes that could contribute to losses caused by unforeseen failure modes. In this study, a preliminary FMEA assessment was performed to identify the failure modes that required a deeper quantitative analysis. In a second step, a quantitative analysis was implemented...

Bridges are an integral infrastructure component and, as such, have been the subject of extensive research efforts related to structural performance. However, there has been little study on the traffic safety performance of bridges, which have very different physical and operational characteristics compared with regular roadway facilities. This study develops safety performance functions (SPFs) for overall vehicle crashes and single-vehicle crashes occurring on major highway bridges in Alabama. The bridge characteristic data and crash information are obtained from three different databases. Geographic information systems (GIS) are used to spatially represent bridges as vectors and associate crashes to the bridges based on location attributes from the crash data. SPFs of several functional forms are developed and investigated for identifying the best model using negative binomial regression. The models are validated by comparing their relative predictive capabilities. This paper recommends models that fit the Alabama data well. These models can be used for estimating the expected number of crashes on bridges along major highways in Alabama.

Structural Engineering International, 2012

The assessment of the structural safety of existing br idges and viaducts becomes increasingly important in many countries owing to an increase in traffic loads. Most existing standards, however, are developed for the design of new structures. For this reason, an assessment method for determining the actual safety level of highway bridges and viaducts has been developed. The method focuses on the determination of the effect of traffic actions and consists of a number of levels. The first level requires the least work from the engineer but is the most conservative. Each of the next levels is less conservative. Some levels require actual measurements at critical parts of the structure. This paper consists of two parts. The first part explains the basis of the safety assessment me thod and the second part shows the step-by-step application of the method to an existing highway bridge in Th e Netherlands.

In this paper, risk assessment for the activities associated with construction of bridge as part of the risk assessment for the project comprising building of new motorway section from Demir Kapija to the village of Smokvica, Republic of Macedonia is presented. After identified risks and hazards, during activities related with bridge works and after performed risk assessment, control measures are proposed.