建设项目投资风险指标及模糊综合度量的研究

风险管理是建设项目管理的一个非常重要的方面,而风险指标是反映建设项目风险状况进行风险分析的一个重要内容.许多的学者对风险指标做过研究,其中大部分涉及的是经济评价和财务评价指标,或者使用损失期望值和方差的代数运算作为指标.本文在分析及总结前人风险指标研究成果的基础上,提出建设项目成本、时间和财务三方面的有关风险指标,并给出各指标的说明和计算公式.为综合评价建设项目的风险,本文利用了效用理论的思想和模糊理论方法,并以实例说明此模糊综合评价的具体计算步骤.     

A new approach for quantitative risk analysis

Project risk management aims to provide insight into the risk profile of a project as to facilitate decision makers to mitigate the impact of risks on project objectives such as budget and time. A popular approach to determine where to focus mitigation efforts, is the use of so-called ranking indices (e.g., the criticality index, the significance index etc.). Ranking indices allow the ranking of project activities (or risks) based on the impact they have on project objectives. A distinction needs to be made between activity-based ranking indices (those that rank activities) and risk-driven ranking indices (those that rank risks). Because different ranking indices result in different rankings of activities and risks, one might wonder which ranking index is best. In this article, we provide an answer to this question. Our contribution is threefold: (1) we set up a large computational experiment to assess the efficiency of ranking indices in the mitigation of risks, (2) we develop two new ranking indices that outperform existing ranking indices and (3) we show that a risk-driven approach is more effective than an activity-based approach.     

A linear Bayesian stochastic approximation to update project duration estimates

By relaxing the unrealistic assumption of probabilistic independence on activity durations in a project, this paper develops a hierarchical linear Bayesian estimation model. Statistical dependence is established between activity duration and the amount of resource, as well as between the amount of resource and the risk factor. Upon observation or assessment of the amount of resource required for an activity in near completion, the posterior expectation and variance of the risk factor can be directly obtained in the Bayesian scheme. Then, the expected amount of resources required for and the expected duration of upcoming activities can be predicted. We simulate an application project in which the proposed model tracks the varying critical path activities on a real time basis, and updates the expected project duration throughout the entire project. In the analysis, the proposed model improves the prediction accuracy by 38.36% compared to the basic PERT approach.     

基于系统双重风险共担的多项目鼓缓冲设置研究

为了提高关键链多项目缓冲管理的效率,首次提出了一种基于多项目双重风险共担的鼓缓冲设置方法。新方法从系统角度分析了多项目不同层级的风险共担作用,以同时落在在子项目关键链和多项目系统关键链上的系统关键活动工期占比为切入点对缓冲进行分层管理,抽取部分项目缓冲集中到系统层面,同时综合考虑风险独立因子以及鼓活动有效产出影响指数对鼓缓冲进行了定量设置。仿真结果表明,本文方法在多项目按时完工率、项目缓冲平均消耗率、系统关键链上鼓活动平均延误百分比、多项目系统总工期和成本这几个绩效方面的表现更优,提高了多项目系统的风险应对能力。     

Cost impact of float loss on a project with adjustable activity durations

Although delays to non-critical activities within the float do not always affect the overall completion time of a project, they commonly cause disputes over the impact cost and apportionment resulting from the complexity of resource utilization in construction projects. Therefore, considerable attention has been focused on providing an effective and reliable method for analysing the effects of float loss. Several recent studies have proposed various methods; however, most of these methods are based on the assumption of a fixed duration for each activity or activity-based cost simulation. Few studies have considered the trade-off between time and costs and the integration of project resources. Using genetic algorithms, this study introduces a critical path method (CPM)-modified resource-integrated optimization model and successfully quantifies the impact of float loss on the total cost of the project. The results provide objective quantification for accurately evaluating the impact of within-float delays and facilitate the analysis of the impact of delay claims on cost and apportionment in construction projects.     

The use of fuzzy variables in pert

In this paper we present a method—called Fpert—for estimating a project completion time in the situation when activity duration times in the project network model are given in the form of fuzzy variables—fuzzy sets on time space. Theoretical foundations of the method as well as results of calculations derived from a simple example are included.     

A hybrid scatter search for the discrete time/resource trade-off problem in project scheduling

We develop a heuristic procedure for solving the discrete time/resource trade-off problem in the field of project scheduling. In this problem, a project contains activities interrelated by finish-start-type precedence constraints with a time lag of zero, which require one or more constrained renewable resources. Each activity has a specified work content and can be performed in different modes, i.e. with different durations and resource requirements, as long as the required work content is met. The objective is to schedule each activity in one of its modes in order to minimize the project makespan. We use a scatter search algorithm to tackle this problem, using path relinking methodology as a solution combination method. Computational results on randomly generated problem sets are compared with the best available results indicating the efficiency of the proposed algorithm.     

Dynamic monitoring and control of software project effort based on an effort buffer

The improvement to the monitoring and control efficiency of software project effort is a challenge for project management research. We propose to overcome this challenge through the use of a model for the buffer determination and monitoring of software project effort. This software project effort buffer was originally determined on the basis of a risk management factor analysis with total consideration for project managers’ risk preference. The effort buffer was next allocated to different stages according to the buffer allocation cardinal. An effort deviation monitoring and control model was then established based on the grey prediction model, including the establishment of a deviation monitoring and control model, a simulation test of the accuracy and the deviation prediction algorithm flow chart. The method system was eventually applied to an actual project and compared with the actual project data. The results show that the relative error test accuracy of the proposed model is qualified according to the test standard of the grey model, signifying that it could be used for the prediction of effort deviation and decision-making. The proposed model could use the dynamic control system to monitor and control software project effort in an effective manner.     

On path correlation and PERT bias

Most studies of project time estimation assume that (a) activity times are mutually independent random variables; many also assume that (b) path completion times are mutually independent. In this paper, we subject the impact of both these assumptions to close scrutiny. Using tools from multivariate analysis, we make a theoretical study of the direction of the error in the classical PERT method of estimating mean project completion time when correlation is ignored. We also investigate the effect of activity dependence on the normality of path length via simulation.     

A new heuristic for resource-constrained project scheduling in stochastic networks using critical chain concept

This paper presents a newly developed resource-constrained project scheduling method in stochastic networks by merging the new and traditional resource management methods. In each project, the activities consume various types of resources with fixed capacities. The duration of each activity is a random variable with a given density function. Since the backward pass method is implemented for feeding-in resources. The problem is to determine the finish time of each activity instead of its start time. The objective of the presented model is defined as minimizing the multiplication of expected project duration and its variance. The values of activities finish times are determined at decision points when at least one activity is ready to be operated and there are available resources. If at a certain point of time, more than one activity is ready to be operated but available resources are lacking, a competition among ready activities is carried out in order to select the activities which must be operated first. This paper suggests a competition routine by implementing a policy to maximize the total contribution of selected activities in reducing the expected project duration and its variance. In this respect, a heuristic algorithm is developed and compared with the other existing methods.     

Using a risk-based approach to project scheduling: A case illustration from semiconductor manufacturing

This paper introduces a risk-based optimization method to schedule projects. The method uses risk mitigation and optimal control techniques to minimize variables such as the project duration or the cost estimate at completion. Mitigation actions reduce the risk impacts that may affect the system. A model predictive control approach is used to determine the set of mitigation actions to be executed and the time in which they are taken. A real-life project in the field of semiconductor manufacturing has been taken as an example to show the benefits of the method in a deterministic case and a Monte Carlo simulation has also been carried out.     

基于控制工序性质的LOB截止日期问题分析与算法

截止日期问题是重复性项目调度中研究最为广泛的问题之一,其旨在满足项目截止日期前提下求得一个工作队雇佣总量最小的调度方案。由于重复性项目往往为大型工程建设项目,一个准确的最优进度计划对于节约项目的资源和成本具有重要意义。在平衡线法(LOB)框架下,本文从控制工序的性质出发,研究并分析了控制工序工作队分配与项目总工期之间的关联,给出了截止日期问题的一些特殊性质。基于这些性质,一方面能够帮助项目管理人员判断一个调度方案是否可行且经济,另一方面能够得到一些有效的剪枝策略,从而设计出具有针对性的分支限界算法。最后,通过案例计算和仿真实验验证了本文提出的算法在计算效果和计算效率上的有效性。     

基于活动延期风险加权时差的资源受限项目调度鲁棒性度量

在项目调度鲁棒性研究中,当活动出现延期风险时,由于各活动性质不同,其延期风险权重也不同,权重越大的活动越有可能影响项目的完工时间。针对资源受限项目调度问题,提出一个基于活动延期风险加权时差的鲁棒性度量新指标。在出现不确定因素干扰时,该指标不仅考虑了活动延期风险权重的影响,同时为实现时差在多个任务之间的共享,还考虑了紧前任务数量的影响。建立一个以加权时差最大化为目标的资源受限项目调度鲁棒优化模型,并针对模型特点,设计了基于禁忌搜索的模拟退火算法。最后,通过算例验证了该度量方式和算法的合理性和有效性,对比分析结果表明所提出的指标优于现有的度量指标,较好地满足了项目调度质量鲁棒性的要求。     

A rule for slack allocation proportional to the duration in a PERT network

In this paper, we define a new rule for the resolution of the slack allocation problem in a PERT network. This problem exists of allocating existing extra time in some paths among the activities belonging to those paths. The allocation rule that we propose assigns extra time to the activities proportionally to their durations in such a way that no path duration exceeds the completion time of the whole project. This time allocation enables us to make a schedule for the PERT project under study. We give two characterizations of the rule and we compare it with others that have been previously defined in the literature.     

Structured construction and simulation of nondeterministic stochastic activity networks

In this work we deal with nondeterministic stochastic activity networks (NDSANs). Their stochastic character results from activity durations, which are given by nonnegative continuous random variables. The nondeterministic behavior of an NDSAN is a consequence of its variable topology, based on two additional features. First, by associating choice probabilities with the immediate successors of an activity, some branches of execution are not always taken. Second, by allowing iterated executions of a group of activities according to predetermined probabilities, the number of times an activity is to be executed is not determined a priori. These properties lead to a wide variety of activity networks, capable of modelling many real situations in process engineering and project management. We describe a simple, recursively structured construction of NDSANs, which both provides a coherent syntactic mechanism to incorporate the two abovementioned nondeterminism features and allows the analytic formulation of completion time. This construction also directly gives rise to a recursive simulation algorithm for NDSANs, whose repeated execution produces an estimate of the probability distribution of the completion time of the network. We also report on real-world case studies, using the Komolgorov–Smirnov statistic for validation.     

Simulated annealing and tabu search for multi-mode project payment scheduling

This paper involves the multi-mode project payment scheduling problem where the activities can be performed with one of several discrete modes and the objective is to assign activities’ modes and progress payments so as to maximize the net present value of the contractor under the constraint of project deadline. Using the event-based method the basic model of the problem is constructed and in terms of the different payment rules it is extended as the progress based, expense based, and time based models further. For the strong NP-hardness of the problem which is proven by simplifying it to the deadline subproblem of the discrete time–cost tradeoff problem, we develop two heuristic algorithms, namely simulated annealing and tabu search, to solve the problem. The two heuristic algorithms are compared with the multi-start iterative improvement method as well as random sampling on the basis of a computational experiment performed on a data set constructed by ProGen project generator. The results show that the proposed simulated annealing heuristic algorithm seems to be the most promising algorithm for solving the defined problem especially when the instances become larger. In addition, the effects of several key parameters on the net present value of the contractor are analyzed and some conclusions are given based on the results of the computational experiment.     

Optimal decision indices for R&D project evaluation in the pharmaceutical industry: Pearson index versus Gittins index

This paper examines issues related to various decision-based analytic approaches to sequential choice of projects, with special motivation from and application in the pharmaceutical industry. In particular, the Pearson index and Gittins index are considered as key strategic decision-making tools for the selection of R&D projects. It presents a proof of optimality of the Pearson index based on the Neyman–Pearson lemma. Emphasis is also given to how a project manager may differentiate between the two indices based on concepts from statistical decision theory. This work demonstrates and justifies the correct use of the Pearson index.     

Project scheduling with finite or infinite number of activity processing modes – A survey

This paper surveys single-project, single-objective, deterministic project scheduling problems in which activities can be processed using a finite or infinite (and uncountable) number of modes concerning resources of various categories and types. The survey is based on a unified framework of a project scheduling model including resources, activities, objectives, and schedules. Most important models and solution approaches across the class of problems are characterized, and directions for future research are pointed out.     

An integrated decision support approach for project investors in risky and uncertain environments

In project investment decisions, it is often assumed that estimated values of project parameters are certain and they would not deviate by the time. However, project parameters normally change during a life cycle of the project. Therefore, an existence of a deviation or gap between forecasted values and actual values is inevitable. Because of the uncertainty of the future, forecasting the true and exact values of project parameters is almost impossible. In this study, an integrated decision support approach based on simulation and fuzzy set theory is proposed for project investors in risky and uncertain environments. This approach determines the risk levels of the projects and helps investors to make investment decisions. In the scope of the study, a flowchart is presented to guide to decision maker in different situations of information uncertainty that belongs to project parameter values. Via this flowchart, the values of project parameters can be chosen depending on how they are determined (deterministic, stochastic or fuzzy) by project analyst. Besides, calculating and analyzing the project risk in all possible situations would be easier. Illustrative examples are given to demonstrate the application of this approach.     

基于容错机制的关键链项目缓冲差别监控研究

关键链项目缓冲监控绩效受活动自身和活动执行主体特性的双重影响,项目经理应根据不同执行主体对活动进行差别监控,而现有缓冲监控研究未充分考虑活动执行主体异质性。首先,结合网络复杂度和风险感知等活动自身因素以及综合信任度等执行主体层面因素对缓冲进行分配;其次,引入容错机制对不同活动触发点进行差别设置,并将缓冲监控分为信任型和监督型两类监控模式;最后,根据活动缓冲消耗对不同活动进行差别动态监控。蒙特卡洛模拟结果表明,本文方法能够有效降低错误预警,保证项目按计划执行并实现对项目的综合优化。