Resource Allocation for Concrete Batch Plant Operation: Case Study

A concrete batch plant is an important element in any concrete construction process, whether it is working as a central mixing plant onsite or is offsite supplying ready mixed concrete to a project. This study tackles the problem of optimizing plant production to maximize profit and, if possible, revenue. A linear programming model has been designed to optimize the plant operation. The maximum production rate for each type of concrete can be obtained by solving the model under the given constraints. A sensitivity analysis is conducted to provide management with a flexible range of prices per cubic yard (cubic meter) and material storage limits. In addition, a model has been designed to determine the optimal number of transit mixers based upon the required quantity of concrete. A chart has been developed to determine the quantities of concrete ingredient materials required daily to organize the available storage space and to plan their delivery.     

Risk Assessment Methodology for Underground Construction Projects

This paper presents a risk assessment methodology for underground construction projects. A formalized procedure and associated tools were developed to assess and manage the risks involved in underground construction. The suggested risk assessment procedure is composed of four steps of identifying, analyzing, evaluating, and managing the risks inherent in construction projects. The main tool of the proposed risk assessment methodology is the risk analysis software. The risk analysis software is built upon an uncertainty model based on fuzzy concept. The fuzzy-based uncertainty model is designed to consider the uncertainty range that represents the degree of uncertainties involved in both (1) probabilistic parameter estimates and (2) subjective judgments. Other tools developed in this study include the survey sheets for collecting risk-related information and the detail check sheets for risk identification and analysis. The paper finally discusses a detailed case study of the developed risk assessment methodology performed for a subway construction project in Korea.     

HKCONSIM: A Practical Simulation Solution to Planning Concrete Plant Operations in Hong Kong

Newly developed approaches for construction simulation have been used to model the one-plant-multisite ready mixed concrete (RMC) production system, validated by real-life operations data in Hong Kong. HKCONSIM—a computer system for simulation modeling and analysis of Hong Kong’s RMC production operations was developed in-house. The system is suitable for the resource provision planning and the production planning of a RMC plant, so as to meet given demands at a number of sites for concrete over a working day. The emphasis of the simulation modeling is on the interactions of multiple sites with the plant, and the objective is to improve the supply service levels and the utilization of plant resources. One significant improvement achieved via the research is that to simulate the RMC production operations with HKCONSIM does not require familiarity by the user with any software-specific terminology and modeling schematics, in contrast with existing simulation methods; the process of constructing a simulation model is reduced to specifying the attributes for each pour and site and providing the plant and truckmixer resources available on self-explanatory on-screen forms. Therefore, by experimenting on a HKCONSIM produced model the user, being a practitioner in the concreting industry, can readily study complicated relationships between the pattern of demand for concrete, the resources available to the system, and the service levels achieved together with the utilization levels achieved for the resources involved. Conclusions are given on the research and recommendations for future work made.     

Decision Making in Flexible Mine Production System Design Using Real Options

Large multifaceted capital projects, such as those in the mineral resource industry, are often associated with diverse sources of both internal and external risks and uncertainties. Risks can cause delays to the planned schedule of a project, add a significant cost, and greatly influence its profitability. Uncertainties can be associated with project risks, as well as with opportunities that can develop throughout the project’s lifecycle. Having the ability to plan for these uncertainties, by incorporating flexible alternatives into the system design, is increasingly recognized as critical to long-term corporate success. This paper advances the knowledge needed to incorporate flexibility in systems engineering and management for both practitioners and researchers. Flexibility is defined in this paper as the ability of a system to sustain performance, preserve a particular cost structure, adapt to internal or external changes in operating conditions, or take advantage of new opportunities that develop during a mine’s life cycle by modifying operational parameters. By engaging in planning for flexible production systems, the effects of risk on a particular project value can be examined, project volatility can be calculated, and potential flexible mining alternatives can be evaluated. Once identified, a real options valuation provides a strategic decision-making tool for mine planners to determine the value of incorporating flexible alternatives into the mine plan. This paper demonstrates that flexibility can become an equal partner among the parameters controlling the decision-making process for underground engineering construction systems, followed by industry practitioners. It presents a methodology in mine production system design by introducing flexibility into design through the application of real options valuation techniques. Real world case studies related to flexible planning and design of construction and production systems in underground hard rock mines are presented.     

Fuzzy Analytical Hierarchy Process Risk Assessment Approach for Joint Venture Construction Projects in China

Research and practice show that construction joint venture (JV) activities in China are opportunities that can bring potential benefits but at the same time may generate many risks. While research has studied these risks and presented useful advice for managing individual risks, the methodologies used to analyze the risks were mainly qualitatively based, and there is a gap in using the quantitative method that can integrate a risk expert’s knowledge to assess the risks associated with JV projects. This paper sets up a hierarchy structure of the risks and then develops a fuzzy analytical hierarchy process (AHP) model for the appraisal of the risk environment pertaining to the JVs to support the rational decision making of project stakeholders. An empirical case study is used to demonstrate the application of the proposed fuzzy AHP model. It is concluded that the fuzzy AHP model is effective in tackling the risks involved in JV projects. The information presented in this paper should be shown to all parties considering JV business opportunities in China, and the proposed approach should be applicable to the research and analysis of risks associated with any type of construction projects.     

基于金属价格不确定性的地下矿生产计划风险分析

针对采用无底柱分段崩落法生产的地下金属矿山的生产计划编制问题,通过构建以净现值（NPV）最大为目标函数并满足生产能力及空间顺序等约束条件的混合整数规划模型,用于确定各个采场之间开采的先后顺序,其中金属价格的变化不仅影响计划编制结果而且使计划的风险显著增大。根据金属历史价格分布,运用几何布朗运动（GBM）模型预测15条金属价格走势曲线,通过求解生产计划的混合整数规划模型,得到不同价格走势下的生产计划结果,然后根据GBM模型预测更多金属价格走势曲线并分析不同计划结果下的净现值、上涨潜力、风险下限、条件风险价值（CVaR）和风险价值（VaR）,最终运用熵值法确定金属价格不确定条件下收益高且风险小的生产计划。经实例验证,此方法科学可行,减少了传统手工方法编制生产计划时受到的价格风险的影响,实现资源低风险高效开采,对指导矿山的实际生产具有重要的意义。     

New Method for Measuring the Safety Risk of Construction Activities: Task Demand Assessment

The task demand assessment (TDA) is a new technique for measuring the safety risk of construction activities and analyzing how changes in operation parameters can affect the potential for accidents. TDA is similar to observational ergonomic methods—it does not produce estimates of probabilities of incidents, but it quantifies the “task demand” of actual operations based on characteristics of the activity and independent of the workers’ capabilities. The task demand reflects the difficulty to perform the activity safely. It is based on (1) the exposure to a hazard and (2) the presence and level of observable task demand factors—that is, risk factors that can increase the potential for an accident. The paper presents the findings from the initial implementation of TDA and demonstrates its feasibility and applicability on two different operations: a roofing activity and a concrete paving operation. Furthermore, the paving case illustrates how the TDA method can compare different production scenarios and measure the effect of production variables on the accident potential. The findings indicate that the method can be applied on activities of varying complexity and can account for several risks and task demand factors as required by the user. The selection of task demand factors is a key issue for the validity of the method and requires input from the crew and safety management. The limitations of the methodology and the need for further research are discussed. Overall, TDA provides a tool that can assist researchers and practitioners in the analysis and design of construction operations.     

New Approach for Modeling the Contribution of NSM FRP Strips for Shear Strengthening of RC Beams

This paper presents the main features of an analytical model recently developed to predict the near-surface mounted (NSM) fiber-reinforced polymer (FRP) strips shear strength contribution to a reinforced concrete (RC) beam throughout the beam’s loading process. It assumes that the possible failure modes that can affect the ultimate behavior of an NSM FRP strip comprise: loss of bond (debonding); concrete semiconical tensile fracture; mixed shallow-semicone-plus-debonding; and strip tensile fracture. That model was developed by fulfilling equilibrium, kinematic compatibility, and constitutive law of both the adhered materials and the bond between them. The debonding process of an NSM FRP strip to concrete was interpreted and closed-form equations were derived after proposing a new local bond stress-slip relationship. The model proposed also addressed complex phenomena such as the interaction between the force transferred to the surrounding concrete through bond stresses and concrete fracture as well as the interaction among adjacent strips. The main features of the proposed modeling strategy are shown along with the main underlying physical-mechanical concepts and assumptions. Using recent experimental data, the predictive performance of the model is assessed. The model is also applied to single out the influence of relevant parameters on the NSM technique effectiveness for the shear strengthening of RC beams.     

Shared symptoms of panic disorder in an elderly couple

To quantify the risk of febrile seizures (FS) in relatives of children with FS and to predict the risk of FS in siblings, we calculated cumulative risks of FS in first degree relatives of 129 children with FS. The study was conducted as a prospective follow up study of FS recurrences at the outpatient clinic of the Sophia Children's Hospital in Rotterdam. Thirteen parents and 12 siblings had experienced FS, accounting for a 6-year cumulative risk of 7%. The risk of FS was increased in relatives of children with recurrent FS (12%). The risk of FS in siblings (10%) in our study was more than twice the average risk in a similar population (4%). A positive FS history in a parent, young age at onset in the proband, and recurrences in the proband were selected in a multivariable prediction model. If two or more of these risk factors were present, the risk of West European siblings to develop FS was 46% (hazard ratio 5.4). CONCLUSION: The cumulative risk of FS in siblings of children with FS is increased. The age attained risk of FS can be estimated using a practical model incorporating three readily available risk factors.     

Development of an automatic response mode to improve the clinical utility of sequential risk-taking tasks.

Sequential risk-taking tasks, especially the Balloon Analogue Risk Task (BART), have proven powerful and useful methods in studying and identifying real-world risk takers. A natural index in these tasks is the average number of risks the participant takes in a trial (e.g., pumps on the balloons), but this is difficult to estimate because some trials terminate early because of the consequences of those risks (e.g., when the desired number of balloon pumps exceeds the explosion point). The standard corrective strategy is to use an adjusted score that ignores such event-terminated trials. Although previous data supports the utility of this adjusted score, the authors show formally that it is biased. Therefore, the authors developed an automatic response procedure, in which respondents state at the beginning of each trial how many risks they wish to take and then observe the sequence of events unfold. A study comparing this new automatic and the original manual BART shows that the automatic procedure yields unbiased statistics whereas maintaining the BART's predictive validity of substance use. The authors also found that providing respondents with the expected-value-maximizing strategy and complete trial-by-trial feedback increased the number of risks they were willing to take during the BART. The authors interpret these results in terms of the potential utility of the automatic version including shorter administration time, unbiased behavioral measures, and minimizing motor involvement, which is important in neuroscientific investigations or with clinical populations with motor limitations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prevention as cumulative protection: Effects of early family support and education on chronic delinquency and its risks.

A cumulative protection model is proposed to explain why chronic juvenile delinquency may be amenable to prevention and how early family support and education may help achieve this important societal goal. A comprehensive review of early risk factors for chronic delinquency is presented with special attention to interactive effects. Interventions combining comprehensive family support with early education may bring about long-term prevention through short-term protective effects on multiple risks. A review of the early intervention literature reveals that the family support component is associated with effects on family risks, while the early education component is associated with effects on child risks. Both components may be necessary for effects on multiple risks and later reductions in delinquency. Implications for social policy and improvement of Head Start are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prototype Model for Build-Operate-Transfer Risk Assessment

The build-operate-transfer (BOT) approach for project delivery, where the private sector has to finance, design, build, operate, and maintain the facility and then transfer it to the government after a specified concession period, is now gaining widespread popularity in developing countries. Compared with conventional project delivery methods, BOT sponsors expose themselves to a high risk, so that special attention must be paid to analyzing and managing risks. The identification, analysis, and allocation of various types of risks are an important aspect for the validation of privately promoted infrastructure projects. The BOT risk model presented in this paper is a prototype evaluation model that provides a logical, reliable, and consistent procedure for assessing the BOT project risk. The proposed model introduced the BOT risk index (F), which relied on the actual performance of eight main BOT risk areas. Two different modeling approaches were used in constructing this index: a new developed and an adapted Dias and Ioannou model. Not only can this index be used for BOT projects’ risk evaluation, but also for ranking them to select the lowest risk project as well.     

Evolving Judgments of Terror Risks: Foresight, Hindsight, and Emotion.

The authors examined the evolution of cognitive and emotional responses to terror risks for a nationally representative sample of Americans between late 2001 and late 2002. Respondents' risk judgments changed in ways consistent with their reported personal experiences. However, they did not recognize these changes, producing hindsight bias in memories for their judgments. An intensive debiasing procedure failed to restore a foresightful perspective. A fear-inducing manipulation increased risk estimates, whereas an anger-inducing manipulation reduced them-both in predictions (as previously observed) and in memories and judgments of past risks. Thus, priming emotions shaped not only perceptions of an abstract future but also perceptions of a concrete past. These results suggest how psychological research can help to ensure an informed public. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quantitative risk assessment for Escherichia coli O157:H7 in ground beef hamburgers

Quantitative Risk Assessment (QRA) is a methodology used to organize and analyze scientific information to estimate the probability and severity of an adverse event. Applied to microbial food safety, the methodology can also help to identify those stages in the manufacture, distribution, handling, and consumption of foods that contribute to an increased risk of foodborne illness, and help focus resources and efforts to most effectively reduce the risk of foodborne pathogens. The term Process Risk Model (PRM) is introduced in this paper to describe the integration and application of QRA methodology with scenario analysis and predictive microbiology to provide an objective assessment of the hygienic characteristics of a manufacturing process. The methodology was applied to model the human health risk associated with Escherichia coli O157:H7 in ground beef hamburgers. The PRM incorporated two mathematical submodels; the first was intended to described the behaviour of the pathogen from the production of the food through processing, handling, and consumption to predict human exposure. The exposure estimate was then used as input to a dose-response model to estimate the health risk associated with consuming food from the process. Monte Carlo simulation was used to assess the effect of the uncertainty and variability in the model parameters on the predicted human health risk. The model predicted a probability of Hemolytic Uremic Syndrome of 3.7 x 10(-6) and a probability of mortality of 1.9 x 10(-7) per meal for the very young. These estimates are likely high for all hamburger meals, but may be reasonable for the home-prepared hamburgers described by this model. The efficacy of three risk mitigation strategies were evaluated by modifying the values of the predictive factors and comparing the new predicted risk. The average probability of illness was predicted to be reduced by 80% under a hypothetical mitigation strategy directed at reducing microbial growth during retail storage through a reduction in storage temperature. This strategy was predicted to be more effective than a hypothetical intervention which estimated a plausible reduction in the concentration of E. coli O157:H7 in the feces of cattle shedding the pathogen and one aimed at convincing consumers to cook hamburgers more thoroughly. The conclusions of this approach are only accurate to the extent that the model accurately represents the process. Currently, uncertainty and ignorance about the hygienic effects of the individual operations during production, processing, and handling limit the applicability of a PRM to specify HACCP criteria in a quantitative manner. However, with continuous improvement through stimulated research, a PRM should encompass all available information about the process, food, and pathogen and should be the most appropriate decision-support tool since it represents current knowledge.     

Applying k-sample tests to conditional probabilities for competing risks in a clinical trial

In the presence of competing risks, a full picture of the data can be developed considering the cumulative incidence function for each risk. If one risk type is of particular interest, the conditional probability of failure due to that risk, conditional on no failure due to the remaining competing risks, can be used to compare any number of samples. Kappa-sample tests of significance are derived and extended to stratified test statistics, allowing adjustment to be made for important prognostic factors. The methods are applied to a clinical trial involving patients with advanced breast cancer, where interest focused on progression of disease at old and new sites. They show that estrogen receptor status positive is an important prognostic factor in terms of time to progressive disease at a current tumour site, even when stratified for a potentially confounding measure of spread of disease, whereas progesterone receptor status positive is important with regard to disease progression at new sites only.     

Understanding the relationship between relative and absolute risk

BACKGROUND: Relative risks are the most common statistics used to quantify the risk of mortal or morbid outcomes associated with different patient groups and therapeutic interventions. However, absolute risks are of greater value of both patient and physician in making clinical decisions. METHODS: The relationship between relative and absolute risks is explained using graphical aids. A program to estimate absolute risks from relative risks is available on the internet (see ftp://ftp.vanderbilt.edu/pub/biostat/absrisk+ ++.txt). This program uses a competing hazards model of morbidity and mortality to derive these estimates. RESULTS: When a patient's absolute risk is low, it can be approximated by multiplying her relative risk by the absolute risk in the reference population. This approximation fails for higher absolute risks. The relationship between relative and absolute risk can vary dramatically for different diseases. This is illustrated by breast cancer morbidity and cardiovascular mortality in American women. The accuracy of absolute risk estimates will be affected by the accuracy of relative risk estimates, by the appropriateness of the reference groups used to calculate relative risks, by the stability of cross-sectional, age-specific morbidity and mortality rates over time, by the influence of individual risk factors on multiple causes of mortality, and by the extent to which relative risks may vary over time. CONCLUSIONS: Valid absolute risk estimates are valuable when making treatment decisions. They can often be obtained over time intervals of 10 to 20 years when the corresponding relative risk estimates have been accurately determined.     

Stochastic Modeling for Pavement Warranty Cost Estimation

This paper presents a cost estimation model for long-term pavement warranties with multiple distress indicators. One application area for such warranties involves performance-based specifications (PBSs). In contrast to traditional approaches, PBS gives contractors the flexibility to select construction methods, materials, and even design. However, the contractors then must warrant the performance of their work for a specified period of time. Therefore, an accurate estimation of the risks associated with the warranty is a significant cost issue for any contractor to cover potential risks while still being competitive in bidding. Quantitative evaluation of the cost of risk incurred by the warranty has several difficulties. The deterioration of a highway project is a complex process, which is affected by pavement structure, material, traffic load, and weather conditions. Based on a probabilistic risk analysis of failures of performance indicators, the resulting model can estimate the warranty cost at a detailed level. The application of the model has been demonstrated via a numerical case study using long-term pavement performance data.     

A new technique for measuring velopharyngeal orifice area during sustained vowel production: an application of aerodynamic forced oscillation principles

A new technique for measuring velopharyngeal orifice area during sustained vowel production is described. The technique is based on a simple oscillatory flow balancing procedure between two aerodynamic branches, a mechanical model of the human upper airway and the subject's upper airway. The area of the velopharyngeal orifice in the model is adjusted until identical oscillatory flows traverse it and the subject's velopharyngeal orifice in response to a common forced oscillatory pressure. When identical oscillatory flows are observed, the area of the adjusted orifice is taken as a measure of the area of the subject's velopharyngeal orifice.