Engineering for Extremes

Buildings, bridges, roads, and other infrastructure essential to our economic and social well-being are at an increasing risk from hurricanes, storms, floods, earthquakes, tsunamis, heat waves, fires, terrorism, climate change and other extreme events. The timing, severity and combination of these extremes are highly uncertain, and are characterised as low probability-high consequence events. The chapter starts by introducing and reviewing basic concepts about risk and cost–benefit analysis of protective measures aim to reduce the vulnerability of infrastructure, and hence reduce the future impacts of extreme events to reveal protective measures that are cost-effective, and those that are not. This literature review justifies the introduction of risk-based decision support that integrates hazard, engineering, and fragility models, as well as economical decision tools to perform a comprehensive assessment of the cost-effectiveness of protective measures. This risk-based decision support will be illustrated with various study cases of engineering for extremes in the following chapters of this book.

Managing the societal risks from extreme events requires making informed decisions. Decisions are in relation to the desired values of probabilities associated with possible consequences, what are unacceptable consequences (including defining their type and duration), and who might be exposed to risks. Different dimensions of risk including probabilities, consequences, and its source have been discussed in the literature. Such dimensions shape decisions about risk. However, in addition to the technical aspects, ultimately managing risk requires socially negotiated rules. This chapter describes how technical risk analysis can be integrated with public values. The chapter starts with a broad definition of risk and defines its different dimensions. Then the chapter defines guidelines for principled compromises in managing societal risks of extreme events. The chapter also defines the roles and scope in this complex process of risk analysis, risk communication, and risk perception. The proposed guidelines can support decision-makers in making more informed and more transparent decisions about safety, sustainability, and resilience.

Our built environment is essential for community health and welfare. Even with proper design and construction to withstand demands imposed by occupancy, service requirements and natural environmental hazards, buildings and other civil infrastructure may be susceptible to damage due to events outside the design envelope, which may include extreme windstorms, earthquakes, flooding, accidents or intentional malevolence. The human and economic losses that result from such damage can be significant. Changes in design and construction practices over the past several decades have made some modern structural systems vulnerable to extreme and abnormal events. Social and political factors also have led to an increase in events that may pose a threat to civil infrastructure. Finally, public awareness of infrastructure performance and safety issues has increased markedly in recent years. The move toward risk-informed design, with its formal tools for analyzing uncertainties and consequences of damage or failures in the built environment, promises a level of coherence in decision-making that cannot be achieved by judgment alone, and increases the likelihood that judgements, when necessary, are consistent with logic and the available data. Codes and standards provide a highly visible forum for demonstrating economic and social benefits of risk-informed design. Chapter 3 explores the prospects of improving engineering practices to enhance facility robustness and to manage the risk of unacceptable damage from low-probability, high-consequence threats.

Approximately $50 billion is spent annually world-wide in the quest to deter or disrupt terrorist attacks to aviation, significant expenditures that have rarely been subject to systematic cost–benefit or risk analysis. This chapter applies that approach, assessing the risks, costs, and benefits of security measures designed to disrupt terrorist hijackings of airliners assuming terrorists arrive at the airport undeterred and undetected. Under those conditions, existing security measures reduce the risk of a terrorist success by over 88%. Another security measure could be added to the existing array: secondary flight deck barriers, lightweight devices that are easy to deploy and stow, installed between the passenger cabin and the cockpit door to block access to the flight deck whenever the cockpit door is opened in flight. These barriers are highly cost-effective and raise total risk reduction to over 96%. The benefit-to-cost ratio of the measure is high at 5.1, and it remains cost effective even if risk reduction is halved and costs are doubled. On the other hand the expensive Federal Air Marshal Service fails a cost–benefit analysis, whereas the Federal Flight Deck Officer program proves to be cost-effective.

Effective building protections against blast loading are important for the protection of people and property. This chapter summarizes existing guidelines for blast load prediction and structural design to resist blast loading effects. Different approaches for explosion source separation and isolation and their effectiveness on reducing blast loading effects on structures are presented and discussed. The blast resistance performances of structural components as well as building strengthening methodology and their effectiveness are discussed. Uncertainties in blast load prediction and reliability analysis of structures with and without strengthening measures against blast loading are presented and discussed.

This chapter presents a probabilistic approach to assess the long-term economic risk and cost-effectiveness of relevant adaptation measures for Australian housing exposed to non-cyclonic extreme windstorms under a changing climate. The proposed method provides decision-support for the long-term adaptation of residential communities to extreme windstorms and climate change. The cost–benefit analysis suggests that, for all considered climate scenarios, strengthening roof cladding connections is not cost-effective, while improving window resistance or installing window shutters is more cost-effective.

Extreme events, especially weather-related events, are the leading cause of power outages in many countries around the world. Hurricanes and tornadoes are especially destructive and have caused billions of dollars in direct losses due to damage to power systems and indirect losses due to power outages. There is, therefore, a need to implement risk management strategies to reduce such losses and ensure that power systems are reliable and resilient. This chapter presents a framework for risk management of electric power distribution systems subjected to hurricane and tornado hazards. Methods for hazard analysis and component- and system-level risk analysis are discussed. Two case studies are presented to demonstrate the application of the framework. Various risk mitigation strategies such as the use of alternative pole material, targeted hardening of systems, regular preventive maintenance, and enhancement of design are considered in the case studies. Risk and cost-benefit analysis methods are presented to evaluate the effectiveness of the various mitigation strategies. A methodology for optimizing the preventive and corrective maintenance of distribution poles to reduce risk and minimize cost is also presented.

With the increasing reliance on the constant flow of electricity, risk-based management strategies are increasingly needed to ensure that with limited available resources, the grid can maintain high reliability and resilience. A growing concern in meeting this objective is the impact of climatic extremes, as the wide exposure of the power grid infrastructure has resulted in a system that is inherently vulnerable to extreme climatic hazards which are exacerbated by climate change. Analyzing the likelihood of damage induced by extreme hazards is critical for developing risk-informed strategies. Overhead structures, in particular, may experience a wide spectrum of damage types and degrees during hurricanes. Beyond the collapse state of transmission towers, which has been investigated in the past, non-collapse damage states in lattice towers require further attention as they can assist with performance-based design, grid recovery planning, and hardening decisions in preparation for extreme events. The present study establishes a set of performance-based limit states for lattice transmission towers subject to wind-induced extreme loadings. Specifically, five damage states including no damage, slight, moderate, and extensive damage, and collapse are defined. These limit states are founded on the nonlinear behavior of lattice towers and the type and severity of failures in tower elements and connections, as they relate to the repair or replacement requirements of towers. Focusing on a double circuit vertical steel lattice transmission tower as a case study, the proposed limit states are evaluated by generating a large number of random realizations of a diverse set of uncertain variables including those related to wind pressure and material properties using Latin Hypercube sampling method. The generated realizations are used in a set of nonlinear pushover analyses to investigate the performance of the tower at various loading levels. Subsequently, multi-state fragility functions are developed via logistic regression. These fragility models constitute a key step toward reliable extreme wind hazard risk assessment of the transmission grid and can assist with risk-informed decision-making in support of a resilient power grid.

Climate change is aggravating the summer heatwaves, making them more severe, frequent and prolonged. During the heatwave period, buildings are overheated due to heat gain from surroundings which poses significant risks to the occupants. Therefore, adapting our buildings to extreme heatwaves is of paramount importance. This chapter aims to identify the factors contributing to overheating buildings and the associated mitigation measures. The identified overheating factors are low energy building design, lightweight construction materials, internal heat gain, occupant behaviour and urban heat island effect. The overheating mitigation measures are divided into four categories (1) Modification of local microclimate, (2) resistance to heat transfer from outdoor to indoor (3) Absorption of transferred heat through thermal mass, and (4) Release of trapped heat from indoor to outdoor. The effectiveness of each mitigation measure category depends on indoor and outdoor environmental conditions. Numerical analysis showed that the risk of experiencing heat stress during extreme heatwave decreases with increasing energy star rating of the houses in Melbourne, Australia. If the entire existing lower energy star rated houses can be upgraded to 5.4 star, the percentage of Melbourne population experiencing six severe heat stress hours will decrease from 50% to only 4% at 36 °C mean outdoor temperature. The heat-related mortality and morbidity also decreases with increasing house energy rating. Net-benefit analysis showed that upgrading the lower energy rated houses to 5.4 star is highly beneficial with net-benefit becoming positive within 2–5 years. Emerging technology like dynamic insulation material (DIM) which changes the resistance of the external walls and ceilings depending on the indoor and outdoor temperature can help to minimise overheating in a highly insualted and air-tight building. Numerical simulation showed that DIM reduces the indoor air temperature in bedroom and living room by up to 1.1 °C and 1.2 °C, respectively, in the case study building in Melbourne, Australia.

This chapter addresses decision-making for improving the resilience of civil infrastructure to extreme events over a broad region. It shows how this was approached for the West Coast Region of New Zealand. The issues were complex and needed a systemic approach. The project’s client required recommendations for improving infrastructure resilience. Our earlier risk-based work provided knowledge of the region and its natural hazards. A strategy for resilience improvement had to show both what interventions would be better value, and also, given a limited annual budget, how improvements could be prioritised over time. Both issues required an assessment of value, and we developed an appropriate resilience metric. Each infrastructure element was given two scores: its vulnerability or lack of resilience, and its significance or the effect of a failure on community resilience. This in turn was measured by community income. An underlying idea was the concept of a virtual pipeline, arising from the fact that infrastructure is mainly concerned with flows—of energy, goods, people, waste and so on.

The Nankai-Tonankai Trough is the primary source region for mega-thrust subduction earthquakes in Japan. In this chapter, a case study for a coastal town in western Japan is presented to assess the earthquake-tsunami risks due to the future Nankai-Tonankai mega-thrust subduction event using a novel earthquake-tsunami risk model. The multi-hazard risk model incorporates stochastic rupture sources, spatially correlated ground motion fields, tsunami inundation simulations, detailed building portfolio data, seismic and tsunami fragility models, and building damage cost estimation. It produces the multi-hazard and single-hazard loss distributions, accompanied by detailed earthquake rupture scenarios, shaking-tsunami hazard intensity distributions, and building damage distributions. Importantly, the new multi-hazard tool facilitates the identification of critical multi-hazard loss scenarios and produces integrated hazard-risk maps that are particularly useful for disaster risk reduction and management purposes.

The cryosphere is a portion of the Earth system where water is in solid form, normally found in the polar and high-altitude regions. With the global warming, it experiences a rapid change and the change is accelerating. This would profoundly impact, not only on climate systems, but also its functions to support our societies, known as cryosphere services. To some extent, it is reflected by more extreme events in the cryosphere, and particularly by increasing slow-onset deterioration of the cryosphere service. In response to the impact, there is an urgent need to build resilience into both service suppliers and beneficiaries, ultimately towards the minimization of their vulnerability and underlying risks to the change. It is therefore of great importance to understand the key processes and attributions of the changing services in the cryosphere, and more importantly, to attain the knowledges on building resilience and advancing sustainable development in the cryosphere regions. In this chapter, we briefly introduce the cryosphere change and their impact on the services, as well as risks arising from the hazards in response to global warming. To adapt to the changing services and mitigate risks, we explore the approach to enhance society’s resilience in the cryosphere, and illustrate by a case study to manage glacier water resources for sustainable agriculture in the Tarim River Basin.

Besides natural hazards, one of the leading causes of bridge collapse is overloading. So for bridge owners, making decisions about heavy vehicle access to the road network is one of their main concerns. On one hand, it is imperative that the public be kept safe through low levels of loading, but on the other, the efficiency of the road network and freight increasingly depend on heavier and longer trucks. This problem is particularly acute when considering massive indivisible loads such as transformers and wind turbine nacelles, for example, which can even be socially and politically sensitive. In this chapter, we review the tiered approaches used for making bridge network access decisions; from the use of basic bridge formulae to advanced probabilistic assessment methods. Broader, we briefly touch on the use of reliability assessment as a basis for making decisions on network-level access, and the change in risk profile in aggregate as a result. Of course, increasingly owners are turning towards gaining more data from their assets using Structural Health Monitoring to support decision-making. Therefore we discuss how its benefits as a decision-making support tool can be assessed using the Value of Information framework. Finally, we discuss why the low probability-high consequence problem of heavy vehicle network access is particularly challenging for human decision-makers, by exploring the cognitive biases that can make for sub-optimal decisions. From this, recommendations are given for some strategies to overcome these biases in the context of heavy vehicle bridge access. In summary, this chapter explores the guidelines, technological, theoretical, and psychological factors that make heavy vehicle network access a challenging topic in engineering systems safety.

Modern industrial societies need efficient and safe transportation systems for their existence and progress. Tunnels form an important component of road transportation systems in many countries. However, significant fire incidents within them have highlighted human safety as a major concern, resulting in considerable changes to the safety requirements to be satisfied during the design and assessment of new and existing tunnels, respectively. This chapter discusses state-of-practice related to the implementation of risk analysis methods in road tunnel projects. It reviews relevant safety criteria in standards and describes basic aspects on risk acceptance and decision-making with respect to the choice of the safety measures to be implemented. This contribution presents the determination of human safety consequences for use in risk analysis by considering design fires, the development and spread of effects of such fires and emergency evacuation of people. The methodology is illustrated via a case study that deals with the re-qualification of an existing road tunnel in Wales.

Engineering structures are sometimes subject to extreme loading events like vehicle impact, gas explosions, fire or terrorist bombing. These events are characterized by very small probabilities of occurrence, but large effects on design loads. Extreme loading events are also characterized by large uncertainty: impact load changes significantly with vehicle mass and speed, explosion pressure waves depend on charge distance and size, etc. Due to large uncertainty in possible loading scenarios, it is often considered that such extreme events may lead to complete loss of load-bearing elements like walls, beams or columns. In this context, the decision to design or strengthen a structure to support eventual loss of a load-bearing element is a typical example of decision making in presence of uncertainty, with obvious impacts on construction costs. In this chapter, we address the cost-benefit of strengthening structures to withstand loss of load-bearing elements. We show how this decision is rooted on the probability of losing the load-bearing element, which should be the result of a risk analysis addressing a structure’s adjacency, ownership and intended use. We also discuss how this decision depends on the aspect ratio of buildings, on strengthening costs, and on the extent of strengthening measures.

This chapter discusses the impact which durability considerations and climate extremes play on the performance of wind turbine structures. An overview of the technological developments in wind energy production, both onshore and offshore, is provided. The rigorous design requirements and specifications, guidelines and codes of practice prescribed for design are discussed. The basis for computational simulations, necessary to model and assess performance is outlined. Characterization of extreme values is discussed and the impact of climate extremes on environmental loads is demonstrated. The impact of deterioration, in the context of the durability of wind turbine towers is evaluated in terms of the probability of exceedance of specified limit states. Finally, discussion is provided around optimal decision-making regarding design, operation and maintenance.

Low alloy or mild steel pipelines operating under high pressures are widely used as economic solutions for oil and gas conveyance in the offshore industry. Protected externally with coatings or concrete, they are prone to corrosion of the internal surfaces. Such corrosion may affect pipeline safety and ability to contain the oil or gas being transported. Herein an overview is given of the principal factors affecting risk and a summary is given of the use of so-called Extreme Value Analysis to quantify the probability of failure of pipe-wall perforation, including prediction of future risk. Attention is given to provide understanding of the corrosion mechanisms involved to ensure risk analysis and prediction are based on sound principles.

Corrosion and natural events are some of the more significant threats for onshore pipelines because of their frequency and potential severity. Corrosion defects reduce the wall thickness and can lead to a burst due to the internal pressure. Extreme events after seismic activity, either by transient (TGD) or permanent ground deformations (PGD), can also affect pipeline integrity, e.g., tension failure. This chapter proposes a combined reliability assessment for a corroded pipeline subjected to TGD using Monte Carlo simulations. It contemplates simulated seismic activity using two Poisson Processes based on historical records and an attenuation law to evaluate a tension failure. The corrosion degradation implements a Lévy Process based on data from In-Line Inspections (ILI), with the possibility of new defects appearing between inspections and the formation of corrosion colonies to determine a burst failure. The proposed approach is illustrated using a real case study.

Scour is one of the most widespread causes of bridge failure worldwide. The magnitude of the river flow at the bridge location is a key factor which directly affects the scour hole depth. Climate change may cause changes in the flow characteristics in a river due to changes in the precipitation patterns and catchment characteristics. In this paper, statistical analysis of the expected maximum annual flow of rivers is combined with the Monte Carlo simulation to estimate the probability of local scour failure. Climate change is assumed to manifest itself through gradual changes in the statistical characteristics of the expected maximum annual flow distributions. Results are presented from a case study using a bridge in the UK, which revealed that a time-dependent increase in the mean of the expected maximum annual flow has a more pronounced effect on scour performance as compared to an increase of its variability alone. Amongst the cases examined, however, the most adverse effect on local scour performance is observed from the simultaneous increase in both mean and variability of the expected maximum annual flow. The results also highlighted the significance of the foundation depth and local scour model parameter in relation to the changing flow characteristics.

Electricity transmission networks, as a critical component of energy systems that drive daily activities in modern society, have often been impacted by bushfires, as evidenced after the 2018 wildfires, California, USA, and the 2019–2020 Black Summer, Australia, both are record-setting in size and destructiveness in their respective regions. Even though the quantitative risk of bushfires to electricity transmission networks are difficult to model and assess as it consists of complex interplay of weather, climate, topography and vegetation, human activities, and the specific characteristics of the network, some recently developed models using physics-based approaches and statistical methods combined with satellite remote sensing technologies have been applied to and shown promising results in case studies. This chapter describes the interaction of bushfire and transmission network, discusses state-of-the-art models of bushfire risk to transmission networks, and provides some thoughts on adaptation and conceptual resilience framework for transmission networks under bushfire attack.

Designers of building and civil engineering structures, using design standards for an extensive scope of common structures, are confronted with the advent of a global climate that is changing at an accelerating rate. This chapter considers the possibilities for the adaptation of the basis of structural design to account for the exceptional uncertainties introduced by climate change. The case study is limited to building structures exposed to relatively mild climate loading, by assessing climate change in the context of the South African Loading Code SANS 10160. Standardized decision-making, based on vulnerability resistant robustness concepts, are demonstrated to be effective against a severely uncertain or ambiguous future climate. The risk and reliability basis of semi-probabilistic limit states design is adapted to account for the ambiguity of the climate during the service life of the structure. The design basis for wind loading is used to review information on climate change, to determine the vulnerabilities of structures and identify related design situations. Adaptation of standard procedures can then be applied in accordance with climate robustness classes. Strategies for advancing the design base for climate change in tandem with advancement of associated information, are proposed to be incorporated into the agendas of committees and organizations involved in the advancement of standards for structural design.

This closing chapter provides a discussion of the political, economic and social imperatives that affect the policy making decision process for extreme events. It shows that the tools are available to inform policy makers to make calm and considered decisions based on risk assessments that considers the preferences of all stakeholders including the public. However, challenges remain if risk-based decisions are to become truly mainstream in the education of engineers and the engineering practice more broadly.