Professor Mark Stewart

Reliability-based safety assessment is used frequently in Europe and elsewhere to assess the need for maintenance and the remaining service life of structures. In order to assess the effect of corrosion, quantitatively, an experimental study was conducted using an accelerated corrosion testing technique. Vibration tests were carried out fortnightly to study its effect on the natural frequency of RC beams subject to corrosion. One beam was taken out and broken every four weeks. The mass losses of steel rebar were measured to determine the corrosion state. The experimental results are used to develop an empirical model that describes the relationship between natural frequency and corrosion loss. The statistics for model error for this relationship were then inferred. A spatial timedependent structural reliability analysis was developed to update the deterioration process and evaluate the probability of structural failure based on vibration results. The performance of RC beams is used to illustrate the reliability analysis developed in this paper. The inspection finding considered herein is the timing of test and the vibration results, which are used to provide an updated estimate of structural reliability. It was found that vibration test findings change, the future reliability predictions significantly. A description of structural reliability and reliability-based safety assessment is also provided, where failure probabilities are compared with a typical target failure probability to illustrate how condition assessment findings can be used to more accurately assess and often increase service life predictions.

The likelihood that anyone outside a war zone will be killed by an Islamist extremist terrorist is extremely small. In the United States, for example, some six people have perished each year since 9/11 at the hands of such terrorists¿vastly smaller than the number of people who die in bathtub drownings. Some argue, however, that the incidence of terrorist destruction is low because counterterrorism measures are so effective. They also contend that terrorism may well become more frequent and destructive in the future as terrorists plot and plan and learn from experience, and that terrorism, unlike bathtubs, provides no benefit and exacts costs far beyond those in the event itself by damagingly sowing fear and anxiety and by requiring policy makers to adopt countermeasures that are costly and excessive. This article finds these arguments to be wanting. In the process, it concludes that terrorism is rare outside war zones because, to a substantial degree, terrorists don¿t exist there. In general, as with rare diseases that kill few, it makes more policy sense to expend limited funds on hazards that inflict far more damage. It also discusses the issue of risk communication for this hazard.

Development of large scale solar farms supported by large numbers of short piles has created new challenges for engineers to address. Solar arrays are highly flexible structures and the piles can be designed to move to enable more cost effective design. The structural reliability of the above-ground pile can be assessed and probabilities of failure for different section sizes calculated. Economic analysis incorporating capital cost and whole-of-life maintenance cost can be performed to work out whether adopting smaller section sizes provide the best cost outcome. Assessment of pile movements using Monte-Carlo calculations, unsaturated soil mechanics and updating material parameters with suction have been performed. The results show that soil movements are typically larger than pile movements and that soil can slip past the pile with no pile movement when the limiting conditions occur. The results also highlight that the largest soil and pile movements occur infrequently as a result of extreme wetting or drying conditions. Structural reliability analyses showed that correlating wind speed and direction results in a lower probability of failure than if wind load is considered to be uncorrelated with wind direction. The outcomes of the assessment were sensitive to the adopted probabilistic model for pile durability. The main limitation of the analyses is that there is limited information in the literature relating to the types of probability distributions and their input parameters. This adds uncertainty to the stochastic analysis.

Explosive blasts and prediction of fatality risks in urban environments is a complicated task due to the variability in blast wave reflection and propagation. The terrorist threats considered in this paper are vehicle-borne improvised explosive devices (VBIED) containing 225 kg or 450 kg of TNT or ammonium nitrate fuel oil (ANFO) detonated in an open street. This paper uses Viper::Blast CFD software to estimate the variability of explosive blast loads using Monte-Carlo sampling. To probabilistically model the blast wave, the paper takes into consideration the variability of explosive charge mass, detonation location, height of detonation, net equivalent quantity, atmospheric pressure and temperature, and model errors. The fatality risk assessment combines lung-rupture, whole-body displacement and skull fracture dependant on the pressure and impulse. It was found that the mean fatality risk for a 450 kg home-made ANFO explosive device detonated at a road T-intersection is 16% for people exposed in the street. If bollards were placed 10 m from the main street then fatality risk for people in the main street is reduced by over 90%. It was found that a deterministic analysis yielded fatality risks 10¿60% higher than a probabilistic analysis, leading to an overly conservative assessment of safety risks.

Mitigation measures such as window shutters can substantially reduce windstorm damage to housing. However, the cost-effectiveness of wind mitigation measures remains unclear when considering influencing factors such as financial protection via insurance, individual risk perceptions and planning time horizons. Economic incentives may also be provided to motivate homeowners to invest in mitigation. In this study, the installation of cyclone-rated window shutters as a mitigation measure for homeowners in Australia is used as a case study. A life-cycle cost analysis in conjunction with a rank-dependent expected utility model are employed to identify economic incentives that are financially attractive to homeowners with different perceived risks and planning time horizons. The effect of home insurance is also taken into account. The results suggest that, as expected, the economic incentives needed to promote window shutters among homeowners decrease with the perceived storm damage risk and planning time horizon. A rebate for shutter installation cost or a discounted insurance premium have been found to be feasible economic incentives considering a typical planning time horizon of ten years. Statistical surveys are needed in future work to calibrate the parameters within the rank-dependent utility model to better represent the risk perceptions of different groups of homeowners.

Person-borne improvised explosive devices (PBIEDs) are often used in terrorist attacks in Western countries. This study aims to predict the trajectories of PBIED fragments and the subsequent safety risks for people exposed to this hazard. An explosive field test with a typical PBIED composed of a plastic explosive charge and steel nut enhancements was performed to record initial fragment behaviour, including positions, velocity, and trajectory angles. These data were used to predict the full trajectory of PBIED fragments using a probabilistic analysis. In the probabilistic analyses a probability of fatality or serious injury was computed. Based on the results presented, many practical conclusions can be drawn, for instance, regarding safe evacuation distances if a person were exposed to a suspected PBIED.

The paper describes a simplified approach to quantifying a reliability-based design load factor (RBDF) for the variability of explosive blast loading. The user can select range and explosive mass variability and model errors to derive RBDFs for pressure and impulse. These algorithms may be easily programmed into a spreadsheet, computer code, or other numerical method. There is a need by military planners to increase the predictive accuracy of collateral damage estimation (CDE) to ensure maximum damage to the target while minimizing harm to nearby civilians. This present paper uses the CDE damage criterion adopted by the USA and NATO to assess damage and safety risks and recommend safe collateral damage distances. Hence, the present paper utilizes RBDFs to simulate collateral damage risks to a hypothetical reinforced concrete residential building from a 2000 lb bomb using the 99th percentile of blast loads, engineering models, and Monte Carlo simulation analysis that considers variabilities of load and resistance. It was found that CDE is sensitive to airblast model errors and variability of structural resistance. It is recommended that these considerations be incorporated into CDE methodology since existing CDE methodology may be non-conservative, resulting in higher risks of collateral damage.

Postal improvised explosive devices (IEDs) provide criminals and terrorists with a convenient mechanism for delivering an energetic payload to an intended victim with little operational risk. Postal IEDs formed 7% of IED attacks reported in the West between 1998-2015, are often dispatched in groups and can bring postal systems to a standstill. Nearly 30% of postal IED explosions occur in the postal worker environment and a third of the casualties caused by postal IEDs are postal workers. Postal IEDs are debatably a reasonably foreseeable cause of harm to postal workers and should be considered under the work health and safety (WHS) constructs of many Western nations. This paper considers this problem, using a probabilistic risk assessment model to inform a cost-benefit analysis considering potential risk reduction options for postal workers. It identifies that the control measures identified were not cost-effective where only the direct WHS costs pertaining to unintentional postal IED detonation within the mail delivery system were considered given the risk levels identified.

Climate change has led to an increase in the frequency and intensity of heatwaves as well as the risk of heat stress within buildings. To provide habitable indoor conditions without air-conditioning during heatwave, residential building energy efficiency need to be upgraded. The aim of this research is to investigate the possible correlation of building energy rating upgrading with heat-related health hazard during heatwave, with case data drawing from Melbourne, Australia. Using building simulations, indoor heat stress conditions of different energy rated houses were calculated using wet bulb globe temperature and discomfort index under the Melbourne 2009 heatwave conditions. The results showed that during three days heatwave period, residents of 0.9 star energy rated house were exposed to extreme heat stress conditions for almost 25 h compared to only 6 h experienced by the occupants of 5.4 star energy rated house. Several robust empirical relationships were proposed to predict deaths, ambulance calls, emergency department presentations and after hour doctor calls during heatwave. It was concluded that mortality rate from a Melbourne 2009 type, as well as, future more intense heatwave may reduce by 90% if entire existing lower energy star rated houses can be upgraded to minimum 5.4 star energy rating.

Random Field theory has emerged in recent years to model the statistical correlation of resistance in concrete structures and to determine its influence on the probability of structural failure. A major shortcoming in the work carried out to date is the spatial variability and corresponding correlation associated with applied traffic loads. In this paper the influence of spatial correlation of both traffic load and resistance is considered in the context of bridge safety assessment. The current study, explores, the nature of the problem by three theoretical examples. As a general trend, examples show that while traffic loads are weakly correlated, load effects are strongly correlated as the same heavy vehicle often causes extremes of load effect in different parts of the bridge which is due to the transverse sharing of load (measured here using a load sharing factor). It is found that the strength of correlation of load effect depends greatly on the load sharing factor which is treated in a simple way in many studies. In a more sophisticated beam-and-slab bridge example, load sharing factors are derived from a finite element analysis to assess transverse load sharing, and are shown to vary by girder number, girder segment and by load location. Despite the fact that load effect at points along the length of a bridge is strongly correlated, the combined influence of correlation in load and resistance on probability of failure is small.

When unexpected and emotion-engaging events become Black Swans and carry an ¿extreme impact,¿ this derives not so much those qualities or from their intrinsic size or importance as from reaction, or overreaction, they generate; but one that is often as extreme and unpredictable as the event itself. Most consequential development in human history, however, stems not from such events, but from changes in thinking and behavior that are gradual and often little-noticed as they occur. In addition, when an unexpected, emotion-grabbing event becomes a Black Swan, the response is likely to become internalized, and getting people to re-evaluate through sensible risk analysis and risk communication is extremely difficult. As part of this, events that are aberrations are often unwisely taken instead to be harbingers ¿ and continue to be so even in the face of repeated disconfirming evidence. An examination of the 9/11 response in the US illustrates these points.

The longer-term serviceability and structural safety of steel infrastructure exposed to seawater conditions may be affected by global warming and by seawater nutrient pollution. These may affect abiotic and biotic (microbial) corrosion. A model for long-term corrosion is developed from data obtained from steel piling exposed for 33 years in a seawater harbour. The effects on corrosion losses on the structural reliability of steel sheet piling as used in harbours world-wide were investigated as a function of seawater temperature rise from global warming and of seawater nutrient pollution. The results show that structural reliability is more sensitive to likely nutrient pollution than to predicted increases in seawater temperature, noting also that global warming also could increase nutrient pollution from anthropological sources.

There are many deterministic blast-load methods currently in use, such as (1) those for the ready calculation of explosive pressure, impulse and duration; (2) the derivation of explosive safety distances; or (3) the determination of safety hazards (and other consequences) following an explosive¿s detonation. In this article, we argue that deterministic blast-loading methods do not fully account for society¿s usual acceptance (or rejection) of the risks associated with damage, safety and/or injury as a result of an explosive blast-load. This article details the state of the art of probabilistic blast-load modelling that supports a quantitative calculation of risk, with respect to damage, safety and injury. The probabilistic models draw data from the literature and from our own field trials. The article details the benefits that flow from this form of blast-load characterisation and concludes with a discussion on how probabilistic methods be used to derive cost¿benefit advice with respect to any proposed risk mitigation solution.

A changing climate which leads to increases in atmospheric CO2 concentration, and changes in temperature and relative humidity (RH), especially in the longer term, will accelerate the deterioration processes and consequently decline the safety, serviceability and durability of reinforced concrete (RC) infrastructure. This paper presents an investigation of carbonation-induced deterioration in three typical Chinese cities (Kunming, Xiamen and Jinan) under a changing climate. The changing trends of atmospheric CO2, local temperature and RH of typical Chinese cities are projected based on the latest CO2 emission scenarios. The time-dependent analysis is based on Monte Carlo simulation, and includes the uncertainty of climate projections, deterioration processes, material properties, dimensions and accuracy of predictive models. Deterioration of RC structures is represented by the probabilities of reinforcement corrosion initiation and damage. It was found that the mean carbonation depths by 2100 may increase by up to 45% for RC structures in China due to a changing climate. It was also found that climate change can cause an additional 7¿20% of carbonation-induced damage by 2100 for RC buildings in temperate or cold climate areas in China. The findings provide a basis for the development of climate adaptation strategies through the improved design of concrete structures.

Capacity reduction factors (¿) for flexure, shear and axial loadings are derived for reinforced concrete (RC) structures based on a reliability-based calibration of the Australian Concrete Structures Standard AS3600. The structural reliability analysis considers the bias and variability of material properties, dimensions, loads and model error. The target reliabilities (ßT) are selected based on consideration of past practice and Australian and international standards. The capacity reduction factors (¿) for the new code AS3600-2009 are selected using the most recent statistical parameters for material strengths for 20¿100 MPa strength concrete using Class N (ductile) 500N reinforcement. The reliability-based calibration found that the ¿-factor can be increased from 0.80 to 0.85 for members in bending, and increased from 0.60 to 0.65 for axial loading of short (stocky) columns where the ratio of the live load to the dead load is at least 0.25. No changes are recommended for shear or torsion, at this time, or for slender columns; further research is needed to better refine the design models for these cases and reduce the variation in their model error. The proposed increases in capacity reduction factors will result in up to an 8.3% increase in design strength that, in turn, provides efficiency in the use of materials. The proposed changes provide for modest savings in greenhouse gas emissions.

Assessment of the reliability of design models developed for Australian Standards is of paramount importance for determination of public safety. Poorly calibrated models and safety factors can lead to overly safe and uneconomic construction or, worse, to an insufficient level of safety. This study investigates the reliability of the models used in the Australian Concrete Structures Standard AS3600¿2009 for the design of beams and slabs in bending and shear and columns under combined bending and axial loading. The study is in two parts; in Part I, strength and variability of over 20,000 concrete cylinders cured under standard conditions and tested at 28¿days are statistically analysed. The data were collected from all cities and regional areas in Australia and for all concrete strength grades; similarly, variability of reinforcement product is analysed. Next, reliable databases of laboratory tests for beams, slabs and columns were established for members failing in flexure, shear and compression and model errors, and their variability, determined for the code design models. It is concluded that improvements in the production of concrete and of bar products, over time, have led to reduced variability in their materials properties¿with potential for increasing code strength reduction factors and, thus, reducing excessive conservatism in design. This is assessed in Part II of this study.

A fragility analysis is conducted for loss of roof cladding for low rise metal-clad industrial buildings located in non-cyclonic regions of Australia. The stochastic analysis includes possible component and connection failures, load redistribution based on progressive failure, spatial distribution of wind load, and internal pressure variation caused by roof sheeting failure. This spatial and time-dependent reliability analysis will enable fragility curves to be developed that relate likelihood and extent of roof cover damage with wind speed. Industrial buildings representative of new construction in the Australian cities of Brisbane, Sydney and Melbourne are considered. Fragility functions are proposed for industrial buildings designed and constructed to existing codes, and also for improperly designed or constructed buildings where a roller door or other dominant opening prematurely fails during a storm for a building designed as nominally sealed. It was found that damage risks double if a roller door or other dominant opening prematurely fails during a storm.

This paper presents an approach for developing a vulnerability model to predict the probability and extent of damage to metal-clad industrial buildings due to extreme wind loading. Structural reliability-based methods that describe the spatially distributed wind load and component/connection strengths probabilistically are used in the model. Two failure mechanisms are considered for the roof envelop, namely; failure of roof cladding, and purlin failure. Interdependency between the failure mechanisms, load sharing effects due to connection/component failure, and internal pressure variation due to roof cladding failure are also considered. The industrial building examined in the study is a hot rolled structural steel, metal-clad, gable-end building designed for cyclonic regions in Australia. The likelihood and extent of roof damage for this buildings is presented using wind vulnerability curves obtained from the probabilistic model. It is found that internal pressure (e.g. an open door) and the use of cyclone washers has a significant effect on wind vulnerability. The utilisation of cyclone washers is found to reduce damage risks by over 70%.

The structural response of typical, gable-end, low roof pitch industrial buildings, in a windstorm is dependent on the wind loads used in the design of cladding and the portal frame structure. Critical, structural wind load effects derived from wind loads measured on a wind tunnel model show that standards such as AS/NZS 1170.2 can produce unconservative design load effects on the heavily loaded fi rst internal frame. This paper forms part of wider study that assesses the vulnerability of hot rolled steel, industrial buildings to wind loads. The knee and ridge bending moments and horizontal and vertical reactions at the base of the frame are the critical load effects that are used in the design of structural members and connections of these types of buildings. This study found that some of these load effects based on external pressures are under-estimated by about 30%, when the building is located in a suburban environment. A dominant windward wall opening can effectively double the design load effects, thus signifi cantly increasing the vulnerability, especially if this scenario has not been considered by the designer.

Columns are the key load-bearing elements in frame structures and exterior columns are probably the most vulnerable structural components to terrorist attack. In this paper, a spatial reliability analysis is conducted to predict the damage for reinforced concrete (RC) columns subject to explosive blast loading. The spatial variability of material and dimensional properties of RC columns are modelled by stationary and non-stationary random fields. The variability of blast loading is also taken into consideration. Monte Carlo simulation and numerical methods are used to derive Blast Reliability Curves for RC columns under explosive loading for a number of terrorism threat scenarios, based on a high-fidelity physics-based computer programme LS-DYNA to estimate design and residual axial load-carrying capacity of RC columns. It was found that spatial variability has a significant effect on structural reliabilities and the spatial model will lead to more accurate predictions of damage and safety risks.

A changing climate and higher wind speeds means that residential construction is likely to receive more damage in the future if design standards are maintained at the current level. The vulnerability of residential construction may be reduced by an adaptation strategy that increases design wind speeds specified by Australian standards. The paper applies break-even analysis to compare the risks, costs and benefits of climate adaptation strategies for new housing in the three largest cities in Australia: Brisbane, Sydney and Melbourne. These cities are located in southeast Australia where wind hazard is dominated by synoptic winds (thunderstorms and east-coast lows). Break-even estimates of risk reduction and adaptation cost for designing new housing to enhanced standards were calculated for three synoptic wind pattern scenarios to 2070: (1) no change, (2) B1 and (3) A1FI emission scenarios. If the actual cost of adaptation exceeds the predicted break-even value, then adaptation is not cost-effective. It was found that this adaptation strategy can lead to risk reductions of 50¿80¿% at a cost of approximately 1¿% of house replacement value. If risk reduction is over 50¿%, discount rate is 4¿%, and there is no change of climate, the break-even analysis shows that adaptation is cost-effective for Sydney if the adaptation cost is less than 5¿9¿% of house replacement cost. Designing new housing to enhance wind classifications is also likely to be a cost-effective adaptation strategy for Brisbane and Melbourne.

Mortar joint thickness has a significant effect on capacity of structural masonry. Data on mortar joint thickness (bed and head joints) were collected from twelve typical storey-high walls at three different building sites and from four walls built in a research laboratory in Switzerland. The data obtained allowed an analysis of the spatial distribution of the joint thickness in each wall and the characterization of the probability distribution of joint thickness. The data has been statistically analysed and the results discussed: the central and dispersion measures were calculated and several probability distributions have been fitted to the sample data and subsequently tested using standard methods of statistical theory. Further, the results obtained from all four building sites have been compared, thus providing quantitative information about the quality of the work on different sites. The presented probabilistic information is then used to define reliability-based limit state specifications where the joint thickness acts as an important random variable. The reliability of the structural masonry subjected to a concentric normal force found that probabilistic modelling of bed joint thickness results in higher reliability indices.

The structural integrity of reinforced concrete (RC) structures in blast events is important for critical facilities. In this paper, a structural reliability analysis is conducted to predict the damage and risk reduction for RC wall panels subjected to explosive blast loading. Due to considerable uncertainties associated with material properties, dimensions, structural response, blast loading, as well as expected damage, probabilistic methods are used in quantifying the probability of damage for conventional and blast-resistant RC precast cladding wall panels by incorporating spatial and non-spatial variables. The variability of blast loading is also taken into consideration. Monte Carlo simulation and numerical methods are utilized to predict damage of RC wall panels subject to various threat scenarios, based on a physics-based computer programme LS-DYNA to estimate maximum support rotations. It was found that spatial variability of concrete compressive strength and concrete cover has little effects on the structural reliability for precast concrete panels, and the blast-resistant wall has 5%-100% lower probability of hazardous failure than the corresponding value for a conventional wall.

Reinforced concrete (RC) structures are subject to environmental actions affecting their performance, serviceability and safety. Among these actions, chloride ingress leads to corrosion initiation and its interaction with service loading could reduce its operational life. Experimental evidence indicates that chloride ingress is highly influenced by weather conditions in the surrounding environment and therefore by climate change. Consequently, both structural design and maintenance should be adapted to these new environmental conditions. This work focuses on the assessment of the costs and benefits of two climate adaptation strategies for new RC structures placed in chloride-contaminated environments under various climate change scenarios. Their cost-effectiveness is measured in terms of the benefit-to-cost ratio (BCR) and the probability that BCR exceeds unity - i.e., Pr(BCR. > 1). It was found that increasing concrete strength grade is more cost-effective than increasing design cover. The results also indicate that the cost-effectiveness of a given adaptation strategy depends mainly on the type of structural component, exposure conditions and climate change scenarios.

Officials serving the public are tasked at the most fundamental level to spend funds in a manner that most effectively and efficiently keeps people safe. To do otherwise is irresponsible. In the case of counterterrorism policy-making, it is important, then, to evaluate the degree to which any gains in security afforded by counterterrorism measures are great enough to justify their cost. Risk analysis is an aid to responsible decisionmaking that does exactly that. We deal with four elements central to this approach-the cost per saved life, acceptable risk, cost-benefit analysis, and risk communication-and we discuss the degree to which risk analysis has been applied within the government to evaluate counterterrorism measures. We summarize our findings when this approach is used to assess the cost-effectiveness of airline and airport security measures, and then conclude by applying it to PreCheck, a measure that seems likely to bring considerable efficiencies to the screening process and great benefits to passengers, airports, and airlines while actually enhancing security somewhat.

Reliability-based design allows the decision maker to select the level of reliability for a specific blast loading scenario and key to this is an understanding of airblast uncertainty. Hence, explosive field trials have been conducted in Australia that measured the variability of free-field blast loading caused by military standard plastic explosives. The results have revealed a high level of variability of peak incident pressure, impulse, and time of positive phase duration for repeatable tests where variability would be expected to be a minimum. The accuracy of predictive blast load models (model error) was also assessed. A probabilistic blast load computer model is revised to capture these observed variabilities. The effect of a 20% mass-increase safety factor typically applied to explosive mass on the probability of exceeding a design blast load is assessed. Reliability-based load factors are calculated where the nominal load is multiplied by the load factor to ensure that the actual load is equal to the reliability level. Reliability-based load factors are estimated for reliability levels of 0.05-0.99, for a range of scaled distances for military munitions. The load factor can be as low as 0.66 for a 0.05 reliability level and as high as 1.30 for a 0.99 reliability level.

Most vulnerability assessments assume that an improvised explosive device (IED) will reach maximum TNT equivalency, and that the IED will successfully detonate. These assumptions will tend to overestimate actual blast-load effects. The paper develops an IED probabilistic risk-assessment model using a systems model for IED attacks based on the reliability of IEDs and by characterizing the human aspects of an IED attack's operational effectiveness from existing databases of terrorist incidents. The analysis includes estimates of the probability of threat, hazard, and loss for large commercial buildings in the United States. It was found that annual fatality risk for building occupants is similar to acceptable risk criteria. This suggests that strengthening buildings against progressive collapse may not be warranted unless there is a specific threat against a building.

Over the years, power distribution systems have been vulnerable to extensive damage from hurricanes which can cause power outage resulting in millions of dollars of economic losses and restoration costs. Most of the outage is as a result of failure of distribution support structures. Over the years, various methods of strengthening distribution systems have been proposed and studied. Some of these methods, such as undergrounding of the system, have been shown to be unjustified from an economic point of view. A potential cost-effective strategy is targeted hardening of the system. This, however, requires a method of determining critical parts of a system that when strengthened, will have greater impact on reliability. This paper presents a framework for studying the effectiveness of targeted hardening strategies on power distribution systems subjected to hurricanes. The framework includes a methodology for evaluating system reliability that relates failure of poles and power delivery, determination of critical parts of a system, hurricane hazard analysis, and consideration of decay of distribution poles. The framework also incorporates cost analysis that considers economic losses due to power outage. A notional power distribution system is used to demonstrate the framework by evaluating and comparing the effectiveness of three hardening measures.

This article assesses the cases that have come to light since 9/11 of Islamist extremist terrorism, whether based in the United States or abroad, in which the United States itself has been, or apparently has been, targeted. Information from them is used to evaluate how the Internet (including various forms of electronic communication) has affected several aspects of the terrorism enterprise in the United States: radicalization, communication, organization, and the gathering of information. In general, it is found that the Internet has not been particularly important. Although it has been facilitating in some respects, it has scarcely ever been necessary. In some respects, the Internet more fully aids efforts to police terrorism ¿ although this is mainly due to the incompetence and amateurishness of would-be terrorists. In other respects, however, the Internet, and the big data compilations it makes possible, greatly increase the costs and complications of the counterterrorism quest.

In this article, we present a simple back-of-the-envelope approach for evaluating whether counterterrorism security measures reduce risk sufficiently to justify their costs. The approach uses only four variables: the consequences of a successful attack, the likelihood of a successful attack, the degree to which the security measure reduces risk, and the cost of the security measure. After measuring the cost of a counterterrorism measure, we explore a range of outcomes for the costs of terrorist attacks and a range of possible estimates for how much risk might be reduced by the measure. Then working from this mix of information and assumptions, we can calculate how many terrorist attacks (and of what size) would need to be averted to justify the cost of the counterterrorism measure in narrow cost-benefit terms. To illustrate this approach, we first apply it to the overall increases in domestic counterterrorism expenditures that have taken place since the terrorist attacks of September 11, 2001, and alternatively we apply it to just the FBI's counterterrorism efforts. We then evaluate evidence on the number and size of terrorist attacks that have actually been averted or might have been averted since 9/11.

The flexural bond strength of unreinforced masonry (URM) is a key material property affecting wall out-of-plane lateral load capacity. It is well known that the unit flexural bond strength (defined here as the flexural strength of the bond between the brick and lower mortar bed joint associated with any given masonry unit (brick)) varies considerably between units, and that this spatial variability might significantly affect the structural performance and reliability of URM walls in flexure. The paper develops a computational method to predict the strength for non-load bearing single skin URM walls subject to one-way vertical bending considering unit-to-unit spatial variability of flexural bond strength. We characterise the probability distributions of wall strength and examine how spatial variability in unit flexural bond strength affects the variability of base cracking load, mid-height cracking load, peak load and behaviour of clay brick URM walls. This is done using 3-D non-linear Finite Element Analyses (FEA) and stochastic analysis in the form of Monte Carlo simulations. Varying COVs (0.1, 0.3 and 0.5) of unit flexural bond strength are considered. The mean and variance of wall strength are estimated to show the effect of spatial variability of flexural bond strength on wall strength. The failure modes of the wall are compared to show the significant differences between non-spatial and spatial analyses. © 2013.

The environment around concrete structures may be influenced by a changing climate, especially in the long run, leading to an acceleration of deterioration. Therefore, the safety, serviceability and durability of concrete infrastructure may decline at a faster rate than expected. Carbonation-induced deterioration to concrete structures constructed in Sydney, Australia and Kunming, China under a changing climate is investigated in this paper. Two emissions scenarios are considered - RCP 8.5 and RCP 4.5, representing high and medium greenhouse gas emissions scenarios respectively. The spatial time-dependent reliability analysis includes time-dependent climate scenarios and deterioration processes, as well as a large number of random variables and spatial random fields of material properties and dimensions. The surface of concrete structures is discretised into a large number of elements and the likelihood and extent of corrosion damage is calculated by tracking the evolution of the corrosion process of each element using Monte Carlo simulations. The results show that a changing climate could cause the extent of damage to increase by up to 6% for reinforced concrete infrastructure in Kunming. The findings may be used to assess climate adaptation measures in the design stage, as well as a cost-benefit analysis of climate adaptation measures.

Climate change may increase atmospheric CO2 concentration and temperature, change relative humidity (RH), and consequently change RC infrastructures' surrounding environment. Especially in the long run, the decline of the safety, serviceability and durability of RC structures may be accelerated. Carbonation induced corrosion damage of RC infrastructure in Xiamen and Shaoguan under a changing climate is investigated for time period 2010~2100. The projection of atmospheric CO2 concentration, temperature and RH in both cities are based on the representative concentration pathways (RCPs). The time-dependent reliability analysis was conducted by Monte Carlo simulation and includes the uncertainty of dimensions, material properties, climate projections, and predictive models. The corrosion damage risks of RC structures are represented by the probability of severe cracking of concrete cover. Results show that climate change may increase mean carbonation depth by 8 mm by 2100. Moreover, carbonation-induced damage risk for RC buildings in temperate areas can be increased by 12%~19%. This research provides a reference for impacts of future climate change on RC structures and development of climate adaptation strategies.

Officials serving the public are tasked at the most fundamental level to spend funds in a manner that most effectively and efficiently keeps people safe. To do otherwise is irresponsible and, because human lives are at stake, immoral. In the case of counterterrorism policy-making, it is important to evaluate the degree to which any gains in security afforded by counterterrorism measures have been great enough to justify their cost. Risk analysis is an aid to responsible decision-making that does exactly that. We deal with four issues central to this approach, applying them to the hazard presented by terrorism: the cost per saved life, acceptable risk, cost-benefit analysis, and risk communication. We also assess the degree to which risk analysis has been coherently applied to counterterrorism efforts in the US in making or evaluating decisions that have cost taxpayers many hundreds of billions of dollars over the past dozen years. © 2014 Taylor & Francis.

The intensity of tropical cyclones and severe storms is likely to increase due to climate change. Brisbane and the northeast coast of Queensland are regions where design wind specifications may be inadequate under either current or likely future climate conditions. An appropriate adaptation strategy may be one that increases wind classifications for new houses, which leads to a reduced vulnerability of new construction. The present paper will assess the damage risks, adaptation costs, and cost-effectiveness of these adaptation measures for residential construction in Cairns, Townsville, Rockhampton, and South East Queensland, assuming time-dependent changes in the frequency and intensity of cyclonic and noncyclonic winds to 2100. Loss functions are also developed for direct and indirect losses. It was found that increasing design wind loads for new houses in Brisbane and South East Queensland will lead to a net benefit [net present value (NPV)] of up to $10.5 billion by 2100, assuming a discount rate of 4%, which includes approximately 95% of a direct benefit and 5% of an indirect benefit. The benefits are highest for Brisbane due to its large population and the high vulnerability of existing residential construction, and have a 90-100% likelihood of achieving a net benefit by 2100.

This paper presents a risk-based framework to assess the hurricane damage risks to distribution poles, and investigates the risks, costs and benefit of different mitigation strategies. It is estimated that power outages due to storms cause approximately $270 million in repair/replacement costs annually in the USA. Hurricane Irene alone left approximately 6 million residents without power along the east coast of the USA in 2011, causing an estimated $5-$7 billion in damages. These high repair/replacement costs warrant an investigation of mitigation strategies that may aid in reducing replacement and damage costs. This paper describes the reliability analysis of typical timber distribution poles and probabilistic wind models to determine failure probabilities for specific locations. Furthermore, in order to more accurately portray the behaviour of distribution poles, the proposed framework includes the degradation and service-proven reliability of timber distribution poles. Four mitigation strategies are developed, and the cost effectiveness of each strategy is evaluated. In order to assess the cost effectiveness, a life cycle cost analysis is conducted for each mitigation strategy. This paper finds that appropriate mitigation strategies can reduce replacement costs of distribution poles associated with hurricane wind by 2060. © 2013 © 2013 Taylor & Francis.

This paper presents a framework to assess the potential hurricane damage risks to residential construction. Studies show that hurricane wind, frequency and/or hurricane-induced surge may change as a result of climate change; therefore, hurricane risk assessments should be capable of accounting for the impacts climate change. The framework includes a hurricane wind field model, hurricane-induced surge height model and hurricane vulnerability models. Three case study locations (Miami-Dade County, FL; New Hanover County, NC and Galveston County, TX) are presented for two types of analyses: annual regional loss estimation and event-based regional loss estimation. Demographic information, such as median house value and changes in house numbers, and distribution of houses for different exposures, is used to estimate the time-dependent probability of damage with or without possible climate change-induced change in wind speed, frequency and/or surge height. Through both analyses, it was found that climate change may have a significant impact on regional hurricane damage losses.

The paper will assess terrorist threats to new and existing bridges and the cost-effectiveness of protective counter-terrorism measures. This analysis will consider threat likelihood, cost of security measures, risk reduction and expected losses to compare the costs and benefits of protective measures to bridges to decide which protective measures are cost-effective. In this paper, a break-even cost-benefit analysis determines the minimum probability of an attack, absent the protective measures, that is required for the benefit of the protective measures to equal their cost for new and existing bridges. It was found that unless terrorist threat probabilities are high, then typical protective measures are not cost-effective. Bridges and other critical infrastructure are subject to a range of natural and man-made hazards, and terrorism is most likely not as important a threat as natural hazards. It was found that economic risks to bridges from floods, earthquakes, and ship impact are higher than threats from terrorism.

Quantified Risk Assessment (QRA) has been in wide use in risk management since the 1960s for systems ranging from aviation, nuclear power, and offshore platforms to medical treatment and pharmaceuticals. The Quantified Tree Risk Assessment (QTRA) system is examined considering the principles of QRA. A case study of 14 fig trees in Newcastle, Australia, illustrates some limitations of the QTRA process, and extrapolating risks for a single tree to a group of trees. There is a need for any risk management process involving trees, not only to assess the risk, but to weigh the benefits provided by trees by a risk-based cost-benefit analysis. Tree risk assessors should rely on benchmarks to ensure that their assessment is not outside of the realms of reality or scientific rigor. © 2013 International Society of Arboriculture.

This paper develops probabilistic and human reliability models to estimate the probability of structural collapse (system risk) during the construction of typical multistory reinforced-concrete buildings in the presence of human error. Results obtained from the human reliability analysis suggest that errors related to concrete cover and concreting workmanship are more detrimental to system risk than any other errors. Errors related to reinforcement area have a minor effect on system risk, provided that the existing effectiveness of engineering inspections is maintained. The results also show that errors related to installation of steel shores/reshores do not significantly affect the system risk. © 2004

The paper considers likelihood and extent of damage to metal roofing of a typical contemporary (new) Australian house subject to non-cyclonic extreme wind loading. A spatial and time-dependent reliability analysis enables fragility curves to be developed that relate likelihood and extent of roof cover loss to gust wind speed. It was found that mean extent of roof damage is less than 1% for a 100-year design wind event, and this estimate includes the effect of a dominant opening and construction defects.

© 9th Asia Pacific Conference on Wind Engineering, APCWE 2017. All Rights Reserved. The paper considers likelihood and extent of damage to metal roofing of a typical contemporary (new) Australian house subject to non-cyclonic extreme wind loading. A spatial and time-dependent reliability analysis enables fragility curves to be developed that relate likelihood and extent of roof cover loss to gust wind speed. It was found that mean extent of roof damage is less than 1% for a 100-year design wind event, and this estimate includes the effect of a dominant opening and construction defects.

There are approximately five million timber power distribution poles in service across Australia worth over $10 billion. Investment in timber power pole infrastructure is even greater in the United States, with an estimated 120 to 200 million U.S. treated poles currently in service. Despite the scale of timber power pole infrastructure assets worldwide, limited research has been carried out to better enhance network maintenance and management efficiency. This paper sets out to examine the structural reliability and performance of timber power pole networks under current and future climatic conditions. The hazards of interest are storm winds and timber decay - both of which may worsen due to a changing climate. The paper presents a case study for Brisbane, Australia, which examines the possible impacts of climate change on power distribution infrastructure. Monte-Carlo stochastic methods were utilised in the form of an event-based sequential model to estimate the climate change impacts over a period from 2015 to 2070, under various climate change scenarios. It was found that predicted climate change impacts are significant, with the analysis indicating that annual pole failures rates could increase by up to 97% under the most severe climate change scenario. The appropriateness of two climate adaptation strategies is also examined herein, via a probabilistic cost-benefit analysis. These adaptation strategies incorporate alterations to power pole design and network maintenance procedures. The analysis indicates that measured changes to design and maintenance procedures can result in costeffective climate adaptation strategies, leading to a notable reduction in potential climate change risks.

The paper develops a Probabilistic Risk Assessment model that estimates of the probability of terrorist threat, hazard, damage and loss for progressive collapse of large federal government buildings in the United States. It was found that the existing annual fatality risk for building occupants are lower than acceptable risk criteria, and that progressive collapse is an exceedingly rare event in Western countries. A cost-benefit analysis of UFC and GSA design provisions to mitigate against progressive collapse showed that these design measures only becomes cost-effective when the threat likelihood is a very high one in a thousand per building per year.

A changing climate may result in more intense tropical cyclones and storms, more intense rain events and flooding, and other natural hazards. Moreover, increases in CO2 atmospheric concentrations, and changes in temperature and humidity, may reduce the durability of concrete, steel and timber structures. There is increasing research that takes into account the changing climate risks and life-cycle costs in engineering to reduce the vulnerability or increase the resiliency of infrastructure - we define this as ¿climate adaptation engineering¿. The paper will describe how risk-based approaches are well suited to optimising climate adaptation strategies related to the construction, design, operation and maintenance of built infrastructure. Stochastic methods are used to model infrastructure performance, risk reduction and effectiveness of adaptation strategies, exposure, and costs. These concepts will be illustrated with state-of-the-art research on risk-based lifecycle assessment of climate adaptation strategies. Uncertainties of climate projections are also discussed. This will pave the way for more efficient and resilient infrastructure, and help ¿future proof¿ new and existing infrastructure to a changing climate.

The paper will assess terrorist threats to bridge infrastructure and the cost-effectiveness of protective and counter-terrorism measures. This analysis will consider threat likelihood, cost of security measures, risk reduction and expected losses to compare the costs and benefits of protective measures to bridges to decide which protective measures are cost-effective. In this paper, a break-even cost-benefit analysis determines the minimum probability of a successful attack, absent the protective measures, that is required for the benefit of the protective measures to equal their cost. It was found that unless terrorist threat probabilities are high, then typical protective measures are not cost-effective. Bridges and other critical infrastructure are subject to a range of natural and man-made hazards, and terrorism is most likely not as important a threat as natural hazards. Economic risks due to terrorism are then compared with risks from flood and seismic hazards. It was found that economic risks to bridges from floods, earthquakes, and ship impact are significantly higher than threats from terrorism. © 2014 Taylor & Francis Group.

Modelling of structural damage caused by explosive blast loads first requires knowledge of the characteristics of the blast load. Most vulnerability assessments assume that an IED will reach maximum TNT equivalency, and that the IED will successfully detonate. These assumptions will tend to over-estimate actual blast load effects. The paper develops an IED Probabilistic Risk Assessment model using a systems model for IED attacks based on IED device reliability and characterising the human aspects of IED attack operational effectiveness from existing databases of terrorist incidents. It was found that it the risk of loss (fatalities, property damage) is influenced more by the operational aspects of an attack (such as target selection, IED placement and attack timing) than the technical aspects of the device (i.e., design and manufacture).

Reinforced concrete (RC) structures deteriorate with time and corrosion of reinforcing steel is one of the main causes for that. In the paper a framework for reliability-based assessment of durability of RC concrete structures in corrosive environments will be briefly described. Existing models for corrosion initiation, corrosion-induced cracking, and effects of corrosion on stiffness and strength of RC members will be considered. Special attention will be paid to the effects of a changing climate on corrosion risks to RC structures.