Sustainability of Bridges: Risk Mitigation for Natural Hazards

Engineering Structures, 2014

This paper presents a Parameterized Fragility based Multi Hazard Risk Assessment (PF-MHRA) procedure risk for assessment of a portfolio of highway bridges subjected to earthquake and hurricane events. As a part of this approach, parametric bridge fragility functions are generated for the two hazards, which are an advance over conventional fragility curves as they can be used for bridges with different geometric and structural properties given exposure to different hazard types. The parametric bridge fragility functions are derived using metamodels and stepwise logistic regression with a non-linear logit function. The relative change in hurricane and earthquake fragilities of the bridges is captured by the parametric fragility functions given variation in design details or geometric parameters of the bridges. These fragility functions are combined with regional hazard data to evaluate annual risk, which is measured as the annual probability of damage. For this purpose, hazard input parameters are identified for earthquakes and hurricane events and a new risk assessment procedure for bridges subjected to hurricane wave and surge loading is also developed. Furthermore, coupling of the risk assessment procedure with parameterized fragilities enables a comparative assessment of the contributions of different hazards to the total risk as the bridge details differ in a portfolio. The proposed framework is applied to multi-span simply supported concrete girder bridges located in South Carolina. The application demonstrates the identification and derivation of input models for the multi-hazard risk assessment for earthquakes and hurricane induced storm surge and wave loading. By applying the proposed method, insights are gained on the influence of different bridge geometries and hazard exposure conditions to the risk of bridge damage. The potential of the proposed procedure to serve as an aid to risk based design of bridges is also highlighted.

Proceedings of the Tenth International Conference on Bridge Maintenance, Safety and Management, 2020

Bridges are crucial points of connection in the transport system, underpinning economic vitality, social well-being and logistics of modern communities. Bridges have also strategic relevance, since they support access to emergency services (e.g. hospitals) and utilities (e.g. water supply). Bridges are mostly exposed to natural hazards, in particular riverine bridges to flooding, and disruption could lead to widespread negative effects. Therefore, protecting bridges enhances the resilience of cities and communities. Currently, most of the countries are not able to identify bridges at higher risk of failure, due to the unavailability of high-quality data, the mixed ownership of the assets or the lack of risk-based assessment approaches. Moreover, current datasets are not accommodating new data deriving from monitoring systems and other technologies. This paper introduces a risk-based approach to bridge management, alongside a preliminary protocolled taxonomy for data collection of bridges.

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.

Engineering Structures, 2003

Decision makers use bridge management systems to determine the optimal allocation of available resources. These systems are currently focused on the structural condition of deteriorating bridges with respect to traffic loads. Bridges, however, are affected by multiple hazards, such as flooding and earthquakes, and not only traffic loading. These multiple hazards should be considered in these management systems when determining the optimal intervention.

2007

The aging of bridges and traffic volume increase result in deterioration of bridge conditions and consequently increased risks to bridges and users. Highway agencies in the United States face challenges because of lack of sufficient resources to maintain bridges in good conditions. Current bridge management practices use cost as the main factor for determining maintenance strategies for bridges. Bridge management methods that identify bridges based on risk considerations and produce cost-effective maintenance strategies are needed to best utilize limited resources for reducing risks associated with bridge conditions. This dissertation proposes and demonstrates a methodology for defining bridge maintenance strategies based on risks associated with conditions of bridge elements and costs needed to improve these conditions. The methodology is a systematic approach for assessing risks to bridge elements based on their failure probabilities and consequences and managing associated risks using cost-effective maintenance strategies. The proposed methodology defines maintenance scenarios, optimal policies that minimize cost of maintenance and risks to elements, and optimal timing for implementing or deferring maintenance policies. The element-level maintenance policies in the proposed methodology are integrated with bridge-level priority ranking to define practical maintenance strategies for an inventory of bridges. The bridges are prioritized for maintenance according to their risk values and risk-reduction effectiveness of their maintenance policies based on benefit-cost analysis. The proposed methodology builds on existing bridge management methods, and allows for the use of risks associated with bridge conditions to assist in making risk-informed decisions for allocating limited resources for cost-effective maintenance strategies of bridges most in need. The study showed that risk is a viable tool for managing the maintenance of bridges in a cost-effective manner. The case study showed that the proposed methodology is feasible and can be implemented in currently used bridge management systems.

Infrastructures

Bridges are essential for guaranteeing the functioning of transportation systems since their failure can cause serious threats to the safety, well-being and economy of modern communities, especially in emergency conditions. Following recent bridge failures, among which include the Morandi bridge in 2018, specific guidelines on risk classification and management, safety assessment and monitoring of existing bridges have been issued in Italy by the Minister of Infrastructure as a mandatory code. They pay particular attention to the evaluation of the residual life span of critical transportation infrastructure dating back to the 1950s and 1960s of the last century. Being a newly issued tool, the Guidelines need to be applied and tested in order to find possible drawbacks and to point out the main factors influencing their results. Therefore, in this study, after a short description of the Italian Guidelines, pointing out some differences with other approaches adopted worldwide, some ad...

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.

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...

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.

Proceedings of the 8th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015)

Highway transportation networks play a vital role in today's economic and societal life and affect growth and employment. Hence, their undisrupted functionality and their quick recovery even after extreme natural hazard events are critical. To this end, resilience assessment of transportation networks against natural hazards is needed for decision-making processes in planning maintenance and retrofit actions, as well as for post-event risk management. This study aims to propose a multi-hazard resilience assessment framework for bridges that are the key components of transportation networks. The first step of the framework is the identification of critical hazards (i.e., earthquakes, floods) and the derivation of hazard curves and scenarios based on their probability of occurrence. The second step consists of a fragility assessment process based on computational analysis for single or multi-hazard occurrences given a range of hazard intensities. The third step includes the evaluation of functionality losses based on fragility assessment. In the fourth step, the required restoration time is estimated, and resilience metrics are calculated as dimensionless indicators. The proposed framework is applied to a case study riverine bridge, and comparative results on the single hazard and the multi-hazard resilience metrics are discussed. It has been observed that the effect of the consideration of multi-hazard scenarios is significant on the resilience of bridges.