Low-probability High-consequence Events Research Articles

Risk-based life cycle cost–benefit analysis for progressive collapse design of RC frame structures

Progressive structural collapse is a typical low-probability high-consequence event. Progressive collapse design can effectively improve the robustness of structures against accidental local damage and reduce the probability of collapse. However, progressive collapse design also increases the construction cost of buildings. Hence, it is necessary to conduct cost-benefit analyses for the progressive collapse design of building structures. This study first designs a reinforced concrete (RC) frame based on a progressive collapse design program that simultaneously optimizes material consumption and structural resistance. Then, the structural failure probability is quantified using an alternative path (AP) method-based fragility analysis that considers the structural uncertainties. Based on this, the life cycle costs and benefits of the structure designed with different design load factors are investigated. A four-story RC frame is used as an example. By considering the time value of money and threat probability, the break-even points and optimized design load factors for the progressive collapse design of the RC frame are analyzed. These research outcomes can help promote progressive collapse design in engineering practice and provide references for proposing scientific and reasonable design load factors.

Can Investment Views Explain Why People Insure Their Cell Phones But Not Their Homes?—A New Perspective on the Catastrophe Insurance Puzzle

The consistently missing demand for catastrophe insurance and for coverage of other low-probability–high-consequence risks is often referred to as the catastrophe insurance puzzle. People show reluctance to insure low-probability–high-consequence events, even with some disastrous consequences, yet insure against small high-probability–low-consequence events. There has been no convincing explanation of this puzzle to this date. This article points out that the underlying rationale may be that individuals interpret insurance contracts with low payout probability as an investment with negative expected net present value. While premium payments start with the conclusion of the contract, usually there is only one loss payment in the near or far future. Using a simple annuity model with fixed annual premiums and expected indemnity payouts, it is found that even an individual characterized by the degree of risk aversion found in the literature is unlikely to purchase insurance with these characteristics. To alleviate this unfavorable insurance purchase syndrome, combining a low-probability with a high-probability loss insurance contract may be a way to incentivize individuals to purchase catastrophe risk coverage.

Risk-averse design of tall buildings for uncertain wind conditions

Reducing the intensity of wind excitation via aerodynamic shape modification is a major strategy to mitigate the reaction forces on supertall buildings, reduce construction and maintenance costs, and improve the comfort of future occupants. To this end, computational fluid dynamics (CFD) combined with state-of-the-art stochastic optimization algorithms is more promising than the trial and error approach adopted by the industry. The present study proposes and investigates a novel approach to risk-averse shape optimization of tall building structures that incorporates site-specific uncertainties in the wind velocity, terrain conditions, and wind flow direction. A body-fitted finite element approximation is used for the CFD with different wind directions incorporated by re-meshing the fluid domain. The bending moment at the base of the building is minimized, resulting in a building with reduced cost, material, and hence, a reduced carbon footprint. Both risk-neutral (mean value) and risk-averse optimization of the twist and tapering of a representative building are presented under uncertain inflow wind conditions that have been calibrated to fit freely-available site-specific data from Basel, Switzerland. The risk-averse strategy uses the conditional value-at-risk to optimize for the low-probability high-consequence events appearing in the worst 10% of loading conditions. Adaptive sampling is used to accelerate the gradient-based stochastic optimization pipeline. The adaptive method is easy to implement and particularly helpful for compute-intensive simulations because the number of gradient samples grows only as the optimal design algorithm converges. The performance of the final risk-averse building geometry is exceptionally favorable when compared to the risk-neutral optimized geometry, thus, demonstrating the effectiveness of the risk-averse design approach in computational wind engineering.

Multi-hazard perceptions at Long Valley Caldera, California, USA

Caldera systems such as Long Valley Caldera, California; Taupo, New Zealand; and Campi Flegrei, Italy, experience centuries to millennia without eruption, but have the potential for large eruptions. This raises questions about how local residents' behavioral responses to these low-probability high-consequence events differ from their responses to events, such as wildfires and earthquakes, that have higher probabilities. To examine this issue, a multi-hazard mail survey of 229 households explored perceptions of—and responses to—volcano, earthquake and wildfire hazards in the Long Valley Volcanic Region. Response efficacy was the only significant predictor of emergency preparedness, which suggests that hazard managers can increase household emergency preparedness by emphasizing this attribute of protective actions. In addition to response efficacy, expected personal consequences, hazard intrusiveness, and affective responses were all significantly related to information seeking. This indicates that hazard managers can also increase households’ information seeking about local hazards and appropriate protective actions by communicating the certainty and severity of hazard impacts (thus increasing expected personal consequences) and that they communicate this information repeatedly (thus increasing hazard intrusiveness) to produce significant emotional involvement (thus increasing affective response).

Multi-Hazard Assessment of Bridges in Case of Hazard Chain: State of Play and Application to Vehicle-Pier Collision Followed by Fire

This study focuses on multi-hazard analysis for bridges, following a two-tier approach. First, it identifies relevant open issues and recent literature developments in the field, presenting data in a meaningful manner, with specific focus on the issues related with the analysis of hazard chain scenario treated as low probability-high consequence events. Second, it describes a practically useful and sufficiently generic approach for efficient computational investigation of hazard-chain scenarios in highway bridges. Following that, the applicability of the approach is exemplified in an appealing and commonly encountered in real-life hazard-chain scenario, in which a multilevel modeling strategy is adopted to assess the structural response under hazard chain scenarios of a highway viaduct. Among the considered scenarios is the impact of a heavy vehicle (tank truck) on the bridge pier, and the fire spread following the collision due to the presence of inflammable material. The bridge structure is a typical 189m long multi-span composite highway viaduct. The impact is modelled with a non-linear transient dynamic analysis that accounts the inertial effect of the global structure, while the fire modelling is performed with non-linear quasi static dynamic analysis focusing on local behavior with a sub-structured model. Then different impact and fire scenarios are considered, including different impact velocities of the truck.

Parameterized fragility analysis of steel frame structure subjected to blast loads using Bayesian logistic regression method

Civil structures might be subjected to blast loads during their lifetime. Since explosion is a low probability high consequence event, the damage assessment of structural system against blast loads needs a probability evaluation approach. This study presented a reliability analysis of steel frame structure against blast loads using Bayesian logistic regression method. Fragility functions parameterized on material properties and blast wave characteristics are developed and further utilized to assess the collapse risk of the structure. The imbalanced data set used in developing logistic regression model and the prediction uncertainty due to the limited data size are particularly stressed. The imbalanced data set is treated by generating synthetic data points for samples that are most likely to be misclassified. The prediction uncertainty is considered by constructing confidence intervals based on the posterior samples generated from Markov Chain Monte Carlo simulations. The developed risk assessment approach is applied to a 10-story steel frame as a numerical example. The probability of structural collapse is obtained and compared with the results from subset simulation method in conjunction with finite element analysis. Results show that the developed parameterized fragility function is accurate in predicting the probability of structural collapse against blast loads compared with the FE-based reliability method. The closed-form fragility function can be implemented to study the effect of parameter variations on the safety of the structure without additional FE simulations.

Inherent Complexities of a Multi-stakeholder Approach to Building Community Resilience

Enhancing community resilience has increasingly involved national and regional governments adopting a multi-stakeholder approach because of the potential interagency benefits. This has led to questions about how best to involve stakeholder groups in translating community resilience policies into practice. This exploratory study contributes to this discussion by addressing two key areas that are fundamental in the concerted effort to build community resilience to natural hazards: (1) stakeholder understanding of community resilience as a concept; and (2) the difficulties associated with the processes of risk assessment and preparedness that stakeholders face locally in building community resilience. Data were collected through semistructured interviews with 25 practitioners and experts within Scotland’s resilience community, and were analyzed through an inductive approach to thematic analysis. These data show how the interpretation of community resilience differs across stakeholder groups. Analysis of the data reveals challenges around the nature of the risk assessment and its role in shaping risk perception and communication. Significant complications occur in communicating about low probability-high consequence events, perceived territoriality, competing risk prioritizations, and the challenges of managing hazards within a context of limited resources. The implications of these issues for policy and practice are also discussed.

Performance-Based Tsunami Engineering for Risk Assessment of Structures Subjected to Multi-Hazards: Tsunami following Earthquake

ABSTRACT Tsunamis are low-probability high-consequence events, usually caused by an earthquake in the ocean and can result in high casualty rates and billions of dollars in damage. Tsunamis can be divided into two main categories: near-field and far-field tsunamis, based on the location of their origin with respect to the site of interest. To perform risk assessment of communities subjected to tsunamis, the current approach would be to use empirical data from historical events, making the data site specific. Recently, researchers have developed approaches to estimate the risk of structures subjected to far-field earthquake generated tsunamis using a simulated tsunami force on a structure numerically. However, for near-field tsunamis, ground motions caused by the earthquake will reach the structure earlier than the tsunami, damaging the structure, which can substantially impair its structural performance in the following tsunami. The multi-hazard case of tsunami following earthquake is discussed herein and a physics-based approach to estimate the risk of structures subjected to them is presented. An illustrative example is presented to elaborate the methodology for a steel building. Successive nonlinear analyses are used to develop fragility functions based on joint earthquake-tsunami intensity measures (spectral acceleration-flow depth-flow velocity). These functions are used in combination with hazard analysis of a specific location to obtain loss estimates. Three different approaches were used for this process and the results showed that the use of the joint three intensity-measure fragilities is essential for the accuracy when estimating damage or structural loss and neglecting their interaction results in substantial errors.

Recent meteorological and marine studies to support nuclear power plant safety in Finland

Major nuclear accidents are typically low-probability–high-consequence events. This paper focuses on weather and sea-level events that might affect the safety of nuclear power plants (NPPs). Flooding risks at Finnish NPP sites have been re-evaluated based on investigations of long-term changes and short-term variations in sea level, which has led to improvements in the protection against extremely high sea water level. Climate change projections indicated that 1000-year return levels of high enthalpy of the air would increase by 13–27% by 2100. However, no clear future trends were projected for the all-year-round probabilities of freezing rain at the NPP sites. Simulations of the spread of hypothetical radioactive releases during two sea-breeze cases, using weather input data at a remarkably high spatial resolution, demonstrated the impacts of coastal meteorological phenomena on atmospheric dispersion. Overviews of various single and combined weather and marine events that could possibly affect normal NPP operation highlighted the need to broaden the scope of future research. Special attention was focused on various aspects of uncertainty. According to the results, a more extreme weather or marine event corresponded to a larger uncertainty in its probability of occurrence in the changing climate.

Minimal Building Fragility Portfolio for Damage Assessment of Communities Subjected to Tornadoes

AbstractTornadoes are considered a low-probability high-consequence event that can cause significant damage to community infrastructure, resulting in injuries and fatalities and ultimately creating...

Changes in Media Portrayal of Human-wildlife Conflict During Successive Fatal Shark Bites

Encounters between humans and wildlife that result in human fatalities can generate public anxiety and increase pressure on conservation managers and governments for risk mitigation. Low probability-high consequence events such as shark bites on humans attract substantial media attention for short time periods, but how the media react when several of these rare but fatal events occur in quick succession has seldom been subject to quantitative analysis. Understanding media portrayal of such encounters is important because it both reflects and influences public perceptions of risks, mitigation measures, and conservation policies. This study examined media portrayals of sharks between 2011 and 2013 in the state of Western Australia during which six shark bites resulting in fatalities occurred. We analysed 361 shark-related articles published in major Western Australian newspapers over 26 months to trace changes in media reporting about sharks prior to, during, and after the six fatalities. The findings indicate that when rare, but fatal human-wildlife events occur in quick succession, negative framing by media of wildlife behaviour and threats can exaggerate public anxiety about the pervasive presence of wildlife predators and high risk of human fatalities. The study highlights the need for government agencies and conservation scientists to better engage with media to provide accurate and effective information and advice to swimmers and surfers about shark ecology and behaviour.

Communicating Low-Probability High-Consequence Risk, Uncertainty and Expert Confidence: Induced Seismicity of Deep Geothermal Energy and Shale Gas.

Subsurface energy activities entail the risk of induced seismicity including low-probability high-consequence (LPHC) events. For designing respective risk communication, the scientific literature lacks empirical evidence of how the public reacts to different written risk communication formats about such LPHC events and to related uncertainty or expert confidence. This study presents findings from an online experiment (N = 590) that empirically tested the public's responses to risk communication about induced seismicity and to different technology frames, namely deep geothermal energy (DGE) and shale gas (between-subject design). Three incrementally different formats of written risk communication were tested: (i) qualitative, (ii) qualitative and quantitative, and (iii) qualitative and quantitative with risk comparison. Respondents found the latter two the easiest to understand, the most exact, and liked them the most. Adding uncertainty and expert confidence statements made the risk communication less clear, less easy to understand and increased concern. Above all, the technology for which risks are communicated and its acceptance mattered strongly: respondents in the shale gas condition found the identical risk communication less trustworthy and more concerning than in the DGE conditions. They also liked the risk communication overall less. For practitioners in DGE or shale gas projects, the study shows that the public would appreciate efforts in describing LPHC risks with numbers and optionally risk comparisons. However, there seems to be a trade-off between aiming for transparency by disclosing uncertainty and limited expert confidence, and thereby decreasing clarity and increasing concern in the view of the public.

The role of public and private insurance in reducing losses from extreme weather events and disasters

This article describes the challenges that victims, insurers and governments face in dealing with insurance for low-probability high-consequence events in both developed and developing economies. In developed economies, given their limited experience with catastrophes, there is a tendency for all three parties to engage in short-term intuitive thinking rather than long-term deliberative thinking when making insurance-related decisions. Here, public-private partnerships can encourage investment in protective measures prior to a disaster, deal with affordability problems and provide coverage for catastrophic risks. Insurance premiums based on risk provide signals to residents and business as to the hazards they face and enable insurers to lower premiums for properties where steps have been taken to reduce their risk. To address issues of equity and fairness, homeowners who cannot afford insurance could be given vouchers tied to loans for investing in loss reduction measures. The National Flood Insurance Program provides an opportunity to implement a public-private partnership that could eventually be extended to other extreme events, while the United Kingdom's Flood Re provides a good case study. In developing economies, insurance penetration is historically very low. This requires innovative solutions to catastrophic risk insurance such as risk pooling, parametric insurance and micro insurance. Nevertheless, the uninsured and uncompensated losses of disasters remain extensive, implying the need for public-private partnerships.

Accidents in the Energy Sector and Energy Infrastructure Attacks in the Context of Energy Security

The risks of technological accidents in the energy sector and their potentially disastrous effects have been analyzed over the past decades, and are nowadays generally recognized to constitute a key factor in an encompassing assessment of energy security. In contrast, the issue of intentional attacks on energy infrastructures has received increased attentionmore recently, particularly due to growing dependence of energy imports fromand transit routes through regions considered less reliable and politically stable. Both types of risks, however, illuminate different vulnerabilities. Therefore, the focus of the present analysis was on these two risk categories: accidents and intentional attacks in the energy sector. Risk assessment resultswere based on quantitative data from the databases ENSAD (Energy-related Severe Accident Database) and EIAD (Energy Infrastructure Attack Database). Evaluations examined similarities and differences between technological accidents and intentional attacks in terms of frequencies and consequences, considering time-series trends and regional patterns. A key difference is that accidents are typically rare and independent events, whereas intentional attacks are often multiple events and concentrated both in time and space, resulting in distinct hotspots. Concerning consequences, the severity distribution for accidents generally stretches over a broad range, with low-probability high-consequence events being an important factor of both energy chain performance and as a measure of risk aversion. On the other hand, these types of consequences are usually less important for intentional attacks because targeted energy infrastructures are often of “linear” nature (e.g. pipelines and transmission lines) that are difficult to protect and usually lead through remote areas with low population density. However, when frequently attacked substantial business and supply disruptions can occur. In summary, the joint analysis of accidents and intentional attacks provides a comprehensive and complementary approach on two types of risks that have rather different properties, but are essential in an energy security perspective.

Homeland security: a case study in risk aversion for public decision-making

Governments and their regulatory agencies normally exhibit risk-neutral attitudes in their decision-making. However, for low probability-high consequence events many decision-makers tend to be risk-averse because of the catastrophic or dire nature of the hazard or event. The degree of risk averseness can be described by utility theory. This paper will infer utility functions that reflect the level of risk averseness of regulatory agencies when adopting new safety measures - such as investing $75 billion per year of the homeland security budget to avert terrorist attacks in the USA. The utility analysis considers threat probability, risk reduction caused by regulatory action, cost of regulatory action, and losses. The expected utilities using an identical risk-averse utility function for: 1 no enhanced security expenditure 2 regulatory action associated with $75 billion of enhanced homeland security expenditure are compared and made equal to each other by modifying the risk-averse utility function. This means that both policy options are equally preferable so if the decision-maker is more risk-averse than suggested by the risk-averse utility function then regulatory action is preferable. It will be shown that the level of risk averseness needed to justify current expenditures for homeland security is considerable.

Contemplating the Role of Precision and Range in Homeland Security Policy Analysis: A Response to Mueller

In an effort to address some of the gaps in homeland security policy analysis—at present a relatively understudied topic from an analytic perspective—Professor Mueller offers an examination of policy decision making for a subset of low probability–high consequence events; particularly the idea of passive asset defense. This article provides a critical examination of Professor Mueller's work, tendering what we identify as a number of critical limitations with his framework and argues it does not provide an adequate basis for sound analysis in this policy area. We also offer several suggestions where one could build upon a portion of the groundwork his paper lays, especially in moving toward a greater appreciation of what terrorism means for an all‐hazards management system.

Tsunami Forces and Effects on Structures

The 2004 Indian Ocean Tsunami claimed more than 220,000 lives. It was a low-probability high-consequence event. A similar disaster could strike elsewhere, particularly in the Pacific but also in Caribbean, Atlantic, and Mediterranean regions. Unlike in seismic ground shaking, there is usually a short lead-time precedes tsunami attack: from a few minutes for a local source to several hours for a distant source. Because mega-tsunamis are rare and because forewarning of these events is possible, the primary mitigation tactic to date has been evacuation. Hence, most efforts have focused on the development of effective warning systems, inundation maps, and tsunami awareness. This strategy makes sense from the standpoint of saving human lives. However, it does not address the devastating damage to buildings and critical coastal infrastructure, such as major coastal bridges, oil and LNG storage facilities, power plants, and ports and harbors. Failure in critical infrastructure creates enormous economic setbacks and collateral damage. The accelerating construction of critical infrastructure in the coastal zone demands a better understanding of design methodology in building tsunamiresistant structures. In some coastal areas such as low-elevation coastal spits or plains, evacuating people to higher ground may be impractical because they have no time to reach safety. In these situations, the only feasible way to minimize human casualties is to evacuate people to the upper floors of tsunami-resistant buildings. Such buildings must be designed and constructed to survive strong seismic ground shaking and subsequent tsunami impacts. The primary causes of structural failure subject to tsunami attack can be categorized into three groups: 1) hydrodynamic force, 2) impact force by water-born objects, and 3) scour and foundation failure. Tsunami behaviors are quite distinct, however, from other coastal hazards such as storm waves; hence the effects cannot be inferred from common knowledge or intuition. Recent research has addressed tsunami forces acting on coastal structures to develop appropriate design guidelines, and mechanisms leading to tsunamigenerated scour and foundation failures. This special issue is a compilation of 14 papers addressing tsunami effects on buildings and infrastructure. The four main groupings begin with two papers on tsunami force acting on vertical walls. Arikawa experimentally investigates the structural performance of wooden and concrete walls using a large-scale laboratory tank in Japan. Also using a similar large-scale tsunami flume but in the US, Oshnack et al. study force reduction by small onshore seawalls in front of a vertical wall. The second grouping focuses on tsunami force on 3-D structures. Arnason et al. present a basic laboratory study on the hydrodynamics of bore impingement on a vertical column. Fujima et al. examine the two types of formulae for tsunami force evaluation: the one calculated from flow depth alone and the other based on the Euler number. Lukkunaprasit et al. demonstrate the validity of force computation recommended in a recently published design guideline (FEMA P646) by the US Federal Emergency Management Agency. The other two papers look into the specific types of structures: one is for light-frame wood buildings by van de Lindt et al, and the other is for oil storage tanks by Sakakiyama et al. The topic of debris impact force is the focus of the third grouping. Matsutomi summarizes his previous research on impact force by driftwoods, followed by the collision force of shipping containers by Yeom et al. Yim and Zhang numerically simulate tsunami impact on a vertical cylinder; this paper is included in this grouping because their numerical approach is similar to that of Yeom et al. As for the fourth grouping, Shuto presents field observations on foundation failures and scours, and Fujii et al. discuss the erosion processes of soil embankments. There are two more papers: those are the application of fragility analysis to tsunami damage assessment by Koshimura et al. and evaluation of an offshore cabled observatory by Matsumoto and Kaneda. The topics presented here are undoubtedly in progress, and many revisions and improvements are still needed in order to achieve better predictability for tsunami effects on buildings and infrastructure. We hope you find the papers in this issue intriguing and the information useful, and become further interested in this important natural hazard. Lastly, we wish to express our appreciation to the authors for their timely contributions, and to the reviewers for their diligent and time-consuming efforts.

The risk-return tradeoff in optimizing regional earthquake mitigation investment

Earthquakes are low probability-high consequence events, regional earthquake mitigation is therefore a risky investment. Despite its importance, the risk-return tradeoff is often not examined explicitly in regional earthquake risk management resource allocation decisions. This paper introduces a stochastic optimization model developed to help decision-makers understand the risk-return tradeoff in regional earthquake risk mitigation, and to help state and local governments comply with the Disaster Mitigation Act of 2000 requirement that they develop a mitigation plan. Taking advantage of the special structure of the optimization, Dantzig-Wolfe decomposition is used as the solution method. A case study for Central and Eastern Los Angeles illustrates an application of the model. Results include a graph of the tradeoff between risk and return, quantification of the relative contributions of each possible earthquake scenario, and discussion of the effect of risk aversion on the selection of mitigation alternatives.

Vulnerability Analysis of Structures

A system is robust if it can withstand arbitrary damage. There are many practical ways to design in robustness but there is no satisfactory measure of robustness. Reliability theory is a useful tool for examining the probability of failure for a pre-defined type of loading, however low probability-high consequence events may be missed. Whilst it is not easy to put forward a unified theory of robustness, one insight into the lack of robustness is gained by identifying how a system is vulnerable. If a system is vulnerable in any one way then it is not robust. Like robustness, vulnerability has been defined differently in different contexts.

The probabilities of sex offender re-arrest.

Estimates of the probabilities of re-arrest for sex offenders apprehended in Western Australia between April 1984 and December 1994 are reported. Of the 116,151 distinct male persons arrested for the first time from 1984 94, 2785 were identified with at least one sex offence. Subjects on average were followed up for 5.7 years and assessed by criminal record, Aboriginality, bail status, age, occupation and penal intervention. Three criteria, rearrest for any, repeat sex or a violent offence are used to summarize the 'careers' of sex offenders. Overall ultimate probabilities of rearrest for any offence were 0.61, for a repeat sex offence 0.33 and for a violent offence 0.51. Probabilities of re-arrest for non-Aboriginal offenders were lower for all definitions. Younger offenders, Aborigines and those with prior arrest for non-sex offences had higher probabilities for any or violent rearrest but older offenders tended to have higher probabilities of repeat sex offending. Community supervision and imprisonment significantly reduced the 'rate' or speed of re-arrest. Actuarial risk assessments for low-probability high-consequence events such as dangerous recidivism are useful for identifying groups with a high probability of rearrest, assisting management of these groups and evaluating penal interventions.