Alan D. Russell

Elicitation of subjective probabilities for economic risk analysis: An investigation

This paper investigates three major issues regarding the elicitation of expert knowledge for economic risk analysis: (1) recognition of some of the implicit assumptions and beliefs; (2) development of an approach to elicit expert knowledge as accurate, calibrated and coherent subjective probabilities; and (3)a study to explore human ability to predict future events and the validity of the implicit assumptions and beliefs in the context of the expert judgements. The proposed elicitation approach combines the theoretical requirements for valid subjective probabilities with a practical process. The recognition that some of the implicit assumptions and beliefs in engineering risk analysis should be explored when dealing with the human ability to predict future events, and the inherent difficulties in developing experiments and methods to test such beliefs arc some of the benefits of the study. Directions for future work are suggested.

Analytical approach for economic risk quantification of large engineering projects: validation

Validation and the computational efficiency of an analytical alternative to Monte Carlo simulation for quantifying risks in project performance measures such as time, cost, net present value and internal rate of return are explored in this paper. The analytical approach is based on the use of the Pearson family of distributions, a four moment characterization of uncertainty for input and output variables and a modified version of the PNET algorithm for modelling time uncertainty. The approach is applied to a generalized hierarchical description of a projects economic structure. Results show that the analytical approach can duplicate results of a full-scale Monte Carlo simulation with approximately 0.033 of the computational effort.

TREATMENT OF CORRELATION FOR RISK ANALYSIS OF ENGINEERING PROJECTS

Abstract Treatment of correlations between variables is necessary to establish realistic quantifications of uncertainty of decision variables such as project duration, cost and internal rate of return during the planning stages of an engineering project. This paper highlights some often ignored theoretical requirements necessary for a rigorous consideration of correlations and presents a general analytical procedure for eliciting and treating correlations between variables which is applicable to a broad class of engineering problems. The general case of a decision variable Y expressed in terms of an arbitrary function g(X) is examined, where X is a vector of random variables, some or all of which may be correlated. The theoretical requirement for a positive definite correlation matrix is described, along with a two stage process that leads to the elicitation of such a matrix. A variable transformation approach for treating correlations in moment analysis is used to derive the first four moments of Y. The ...

Analytical approach for economic risk quantification of large engineering projects

A consistent,four moment based approach for quantifying time and economic risks is presented. The goal is to produce a computationally efficient tool that can be used to explore economic feasibility and tradeoffs between cost and time performance versus risk as a function of various strategies for executing and sequencing major work packages. A three level hierarchy of parameters is used, starting with time, cost and revenue performance at the work package/revenue stream level to rate of return at the overall project level. Use of a four moment approach and Pearson distributions at all levels of the hierarchy permit the formulation of a consistent and readily automated approach to risk measurement. Treatment of correlations is included. A modified form of PNET is presented for quantifying time uncertainty. Use of limiting values (0, 1) of the PNET transitional correlation provide bounds for decision parameters.

STATE-OF-THE-ART REVIEW OF CONSTRUCTION PERFORMANCE MODELS AND FACTORS

Measuring and assessing construction project performance on an ongoing basis is an important part of management and control of a project. Described in this paper is the current state-of-the-art of research on prediction and explanation of construction project performance gleaned through an extensive literature search that identified 122 relevant articles published over the last 20 years. This review was carried out in support of an ongoing research program that seeks to embed within a decision support system a transparent reasoning schema that operates on fundamental relationships amongst influencing factors as well as user-defined, experience-based hypotheses for explaining project performance. Findings from the review are presented in two tables that identify performance measures treated (productivity, time, cost, scope, quality, safety, project success and others), level of analysis (overall project, work package, individual activity), and factors that affect performance outcomes. The paper concludes with a discussion of the findings in terms of areas of consensus, knowledge gaps, and steps to be pursued to develop a robust and practical schema for interpreting project data in order to explain the basis for performance to date.

Decision framework for fast-track construction: A deterministic analysis

A deterministic analysis framework that permits the computation of an upper bound on the constant dollar expenditure that should be made to fast-track a project to achieve a specified duration is presented. It employs a baseline plan which corresponds to the traditional method of sequential design, construct, commission and operate, and the economic principle that one will continue to spend as long as the return on the incremental investment equals or exceeds the minimum attractive rate of return. The analysis is based on a generalized definition of fast-track construction, which includes ouerlapping of the construction and revenue phases and acceleration as well as overlapping of design and construction. An example is giuen to illustrate application of the framework.

Object-oriented knowledge frameworks

This paper introduces a strategy for the construction of object-oriented knowledge frameworks. Global control programs, which are traditionally used for manipulating structured representations, have been replaced by domain-specific resources. This new approach offers increased efficiency and simplified development of knowledge-based expert systems for problem domains that deal with a variety of complex structured information.A theoretical foundation is laid for the representation of knowledge, starting with the adoption of a simple schema for structuring stereotypical information. Data and method abstraction is achieved by installing knowledge frames into part of an object-oriented class system that supports procedural attachment and object communication. This allows frame specialization using domain-specific resources and subsequent construction of modular systems with these specialist frames. Editors are introduced for the alteration of data primitives used in declarative representation. Algorithms, which operate on these data primitives, are given for frame instantiation, data access, and user-directed inference.Examples from structural engineering are used throughout the paper to illustrate the practical application of object-oriented knowledge frameworks.

Computer system for the selection of trenchless and conventional methods for underground utilities

Abstract This paper describes the current status of an ongoing research project, the goal of which is to develop a knowledge-based methods-selection tool that can assess specific construction conditionsagainst the capabilities and limitations off available techniques to determine the best method(s) for a specific project. A flexible system architecture is presented which consists of a Standards Level, a Project Level, and an interface between the two. The Standards Level facilitates the capture of experience, expertise and market information about current methods and supporting resources as well as standard descriptions of project elements. The Project Level provides a description of the physical elements and the site context for a given project along with the methods selected for the various steps in the construction process. The interface permits the easy use of coded knowledge, and allows the user discretion in the level of assistance the system should offer in selecting construction methods and formulating an overall game plan. The system architecture builds on a specific vocabulary and supporting constructs for describing methods. Elements of this vocabulary include Method Statement, Operation, Method Class, Method, Resource Class and Resource. The installation of underground utilities using both trenchless and conventional technologies provides a context for the work, and is used in the paper to illustrate the concepts developed.

Fuzzy logic modeling of causal relationships-case study: reasoning about construction performance

Described in this paper is a logic-modeling framework, based on fuzzy neural networks (FNNs) to identify causal relationships among variables. A case study is presented from the industrial construction domain to demonstrate the capability of the proposed system in finding plausible explanations of observed performance failures.

Searching for value: construction strategy exploration and linear planning

Examined is how contractor or construction manager decision making and judgment in response to client objectives and project constraints can be aided by a structured approach to construction strategy selection and assessment using time-space project process and product modelling. The context studied is one of high-rise construction. Construction strategy is expressed in terms of strategy modes and tactical variables and accompanying values, which in turn are expressed in terms of a formal plan using a linear planning modelling paradigm. Highlighted is the important role that data visualization can play in both formulating strategy and assessing its workability via the medium of linear planning graphics complemented with other data representations that make use of quantitative product model data. Of particular interest is the ability to formulate and assess alternative construction strategies in a relatively fast and cost effective manner in order to achieve best value as a function of project constraints, context, and project participant objectives. Included in the assessment task is consideration of the impact of strategy on construction process productivity and production rates by way of performance metrics that relate directly to strategy workability. The concepts presented are illustrated through their application to a large-scale, mixed-use project.