Reliability Buffering for Construction Projects

Buffering is a common practice in project planning. Project managers or schedulers have used a time contingency to guarantee the completion time of either an activity or a project. This traditional buffering, however, often fails to protect the project schedule performance, resulting in an unnecessary resource idle time. To deal with this problem, reliability buffering, a simulation-based buffering strategy, is presented. Reliability buffering aims to generate a robust construction plan that protects against uncertainties by reducing the potential impact of construction changes. The effectiveness of reliability buffering is examined by simulating a dynamic project model that integrates the simulation approach with the network scheduling approach. The research results indicate that reliability buffering can help achieve a shorter project duration without driving up costs by pooling, resizing, relocating, and recharacterizing contingency buffers. A case study of bridge construction projects also demonstrates how construction projects can benefit from reliability buffering in real world settings. Although further validation is needed, reliability buffering can potentially impact the planning and control of construction projects by improving the consideration of construction feedbacks and characteristics in buffering, and serving as an input to a dynamic project model.     

Quality and Change Management Model for Large Scale Concurrent Design and Construction Projects

Concurrent design and construction has been lauded for streamlining projects in terms of time. However, such an approach may actually make projects more uncertain and complex than the traditional sequential design and construction process. The main sources of risk that have been identified with concurrent design and construction are iterative cycles that result from unanticipated errors and changes and their subsequent impacts on project performance. As an effort to address these detrimental impacts, a framework for quality and change management that identifies those negative iterative cycles is proposed. The proposed framework is incorporated into the system dynamics model of dynamic planning and control methodology (DPM), which has been developed to evaluate negative impacts of errors and changes on construction performance. Relevant to practitioners and researchers, the potential of DPM as a robust design and construction planning methodology that could effectively deal with errors and changes inherent in the design and construction process is demonstrated through a case study involving the Treble Cove road bridge in Massachusetts.     

Site Management of Work-in-Process Buffers to Enhance Project Performance Using the Reliable Commitment Model: Case Study

Buffers have been commonly used as a production strategy to protect construction processes from the negative impact of variability. Construction practitioners and researchers have proposed several buffering approaches for different production situations and contexts. However, these solutions have been impractical for managing buffers. To overcome this, this study proposes a new site methodology for managing work-in-process (WIP) buffer in repetitive projects, on the basis of the reliable commitment model (RCM). RCM is a decision-making tool based on lean principles, which uses statistical models to develop more reliable work plans at the operational level. RCM helps to manage WIP buffer in work plans by using site information and planning reliability indicators that result in improved project performance, such as labor productivity and process progress. A repetitive building project was used as a case study. The main finding was that labor productivity, process progress, and waiting times improved when using larger WIP buffers than those typically used among crews. This shows the potential of RCM as a practical tool to manage WIP buffer sizes and to promote the use of lean production strategies at the operational level.     

Web-Enabled System Dynamics Model for Error and Change Management on Concurrent Design and Construction Projects

Construction projects are uncertain and complex in nature often because of iterative cycles caused by errors and changes. These errors and changes impair project performance and, consequently, cause schedule and cost overruns to be prevalent. Iterative cycles are more detrimental when design and construction are concurrent and often force activities to proceed without complete information. In an effort to address this issue, this paper presents the information technology aspect of the dynamic planning and control methodology (DPM), which provides a mechanism that will analyze the impact of negative iterative cycles on construction performance. In order to guarantee a smooth application of this method to real-world projects, DPM has been developed by integrating several existing methods around a core system dynamic model for quality and change management and then implementing these methods into a web-based collaborative environment. A case project, applying the developed web-based DPM, shows great potential in facilitating on-site decision making by virtue of its support of data analysis as well as real-time information sharing.     

Role of Inventory Buffers in Construction Labor Performance

Buffers of material stockpile (inventory) are formed at the work level in construction to help manage production. The size of material stockpiles often has an important bearing on construction project performance. In construction projects, where conditions are often uncertain and variable, some have suggested that buffers be sized and located according to the conditions. New management thinking like lean construction and theory of constraints suggests that the size of buffers needs to be managed carefully, because when oversized, buffers are wasteful, impede workflow, and hinder performance. Research has shown that project variability can be affected with the careful deployment of buffers but has not really evaluated the impact on construction labor performance. This paper reports an exploratory analysis of the relationship between inventory (buffers) and construction labor performance with data collected from three commercial projects in Brazil. In this study, the size of the buffer between rebar fabrication and installation in the construction of a structural system is compared to the labor performance of the fabrication and installation crews. The results show that some buffer helps achieve the best labor performance in the construction operations studied.     

Dynamic Planning and Control Methodology for Design∕Build Fast-Track Construction Projects

A dynamic planning and control methodology is developed by integrating the applications of axiomatic design concepts, concurrent engineering concepts, the graphical evaluation and review technique (GERT), and the system dynamics modeling technique. The goal of the proposed methodology is to help create a dynamic project plan for design∕build fast-track civil engineering and architectural projects where unforeseen changes can be absorbed in the project schedule without creating major interruptions. The axiomatic design concepts are applied to formulate and evaluate various work methodologies, and to create a project plan based on the selected work methodology. The concept of concurrent engineering is adapted to develop a fast-tracking framework based on the task production rate, the upstream task reliability, and downstream task sensitivity to the upstream error. The GERT diagramming scheme is used to calculate the project duration probabilistically by incorporating the possible branches and loops in the project. The system dynamics modeling technique is applied to analyze the causality links of relevant factors in the construction system, and further identifies the important variables that determine the success of a particular overlapping strategy. Consequently, with a rigorous and systemized methodology to help project planning, potential problems can be addressed early before construction. The overall increase in productivity and efficiency as a result of a better planning process can consequently promote the competitiveness of the construction industry.     

Improving Planning Reliability and Project Performance Using the Reliable Commitment Model

Commitment planning reliability at an operational level is a key factor for improving project performance. In the last 15 years, the Last Planner System, a production planning and control system based on lean production principles, has improved commitment planning reliability in the construction industry. However, many construction decision makers continue to rely on their experience and intuition when planning their commitments, which hinders their reliability. The reliable commitment model (RCM) is proposed to improve commitment planning reliability at the operational level by using statistical models. RCM is an operational decision-making tool based on lean principles that supports short-term forecasting commitment planning using common-site information such as workers, buffers, and plans. RCM was tested in several case studies, demonstrating its production forecasting capabilities and its ability to help increase commitment planning reliability and improve project performance. RCM also supports workload and labor capacity matching decisions. RCM has the potential of becoming a useful production decision-making tool.     

C60粉煤灰高性能混凝土的试验研究

C60粉煤灰高性能混凝土,可满足城市的基础设施和工业设施的建设,加快施工进度,降低工程造价,达到节约资源、能源和保护环境的目的.     

Constraint-Based Planning with Integrated Production Scheduler over Internet

Identifying and removing constraints from bottleneck activities help to reduce uncertainties in construction processes and increases the transparency of project management. The present means of look-ahead planning do poorly in resolving hidden constraints in the supply chain and information flow. Accordingly, work plans are vulnerable to the uncertainties that result in flow variation. It has been realized that reducing and eliminating critical constraints through better means of look-ahead planning are the keys to achieving reliable workflow and, consequently, increased productivity. This paper presents a constraint-based planning tool, Integrated Production Scheduler (IPS), to enhance planning reliability while adopting lean construction principles and the theory of constraints. Unlike the critical path method, the IPS models two additional types of constraints related to resource supply and information exchange. It employs four activity buffers: working, shielding, pulling, and screening for managing critical constraints and shielding the production from uncertainties. The implementation of the IPS is prototyped as a distributed scheduling system using Internet technologies such as Java and XML. It facilitates setting up a transparent project management environment where faster communication and active collaboration among project members are achievable.     

Modeling Cost Escalation in Large Infrastructure Projects

Cost overruns in large infrastructure projects have been commonplace in the past decades. Budgeting for cost escalation is a major issue in the planning phase of these projects. In this paper, we first review various methods of forecasting escalation factor and study the changes in construction costs in the past 25 years by analyzing movements of a cost index. We then introduce a system for modeling the escalation uncertainty in large multiyear construction projects. The system uses a Monte Carlo simulation approach and considers variability of project component durations and the uncertainty of escalation factor during the project lifetime and calculates the distribution for the cost. System application is demonstrated using a numerical example. The system can be used by planners and cost estimators for budgeting the effect of cost escalation in large projects with multiyear schedules.     

Risk Allocation by Law—Cumulative Impact of Change Orders

Change, defined as any event that results in a modification of the original scope, execution time, or cost of work, is inevitable on most construction projects due to the uniqueness of each project and the limited resources of time and money available for planning. There are many factors that may cause a change such as design errors, design changes, additions to the scope, or unknown conditions in the field. For each change, contractors are entitled to an equitable adjustment to the base contract price and schedule for all productivity impacts associated with the change. The focus of this paper is to outline the types of changes that can occur on a construction project and also to spell out the financial recovery possibilities that exist for the contractor for each type of change. There are many historical and current court decisions that shape the outcomes of such claims and determine who holds the risks associated with various project changes. Also, an effective cumulative impact claim contains certain vital elements upon which the final outcome will be determined by the legal system. Last, there are certain actions that a contractor and owner can do to either enhance or mitigate the effectiveness of a potential cumulative impact claim.     

Contributors to Construction Debris from Electrical and Mechanical Work in Hong Kong Infrastructure Projects

The crucial problem of construction debris is of increasing concern in Hong Kong. In the construction industry, the electrical and mechanical (E&M) installations in the infrastructure, for example, buildings, tunnels, or dams, are some of the major and usually complex components. Difficulty in coordinating the various trades affects productivity in general, and has a major impact on the quantity of construction debris. By identifying the sources of waste at each stage of E&M engineering work, some of the construction debris can be eliminated at the source during production. This paper investigates the critical production shortcomings in the E&M sector in Hong Kong. The study is based on a survey that includes a preliminary questionnaire survey, brainstorming exercises with a focus group, structured interviews with experienced frontline supervisors, and a second focus group exercise to test findings and proposed measures. The principal findings are that “poor coordination” and “design changes and/or errors” are major contributors to variations or change orders and rework, which in turn result in a high volume of construction debris. The results also indicate that construction debris can be minimized in the E&M sector of the construction industry, if the material wastes from incidental work are reduced and also controlled better in a new work process flow pattern through recommended construction project management improvements for reducing critical production shortcomings.     

Design Error Classification, Causation, and Prevention in Construction Engineering

Construction and engineering practitioners have found it increasingly difficult to learn from their mistakes, particularly with regard to the prevention, identification and/or containment of design errors. Yet, design errors have been the root cause of numerous catastrophic accidents that have resulted in the death and injury of workers and members of the public. This paper examines and classifies the nature of error and design error causation in construction and engineering projects. A review of the normative literature revealed that design errors are caused by an array of factors that can work interdependently. A generic framework is developed that classifies design error according to people, the organization, and project is presented. The paper suggests that people, over and above organizational and project management strategies, have the greatest propensity to reduce errors through the process of situated learning and knowing. This is because the working environment provided by an organization and the processes used to deliver construction and engineering projects influence the nature and ability of people to undertake tasks. Consequently, there is no single but rather a multitude of strategies that need to be adopted in congruence to reduce design errors so that safety and project performance are ameliorated.     

Uncertainty Analysis of Conventional Water Treatment Plant Design for Suspended Solids Removal

An approach that links a Monte-Carlo simulation based reliability program with the water treatment process behavior and performance model is presented for uncertainty analysis of the conventional water treatment plant (WTP) design. The expected mass concentration of suspended solids (SS) in the effluent water is employed as a measurement of system reliability. The approach for uncertainty analysis of a WTP is illustrated with a hypothetical case study. The parameters contributing significantly to the variability of SS concentration in the effluent water are identified. From an operational viewpoint, the variability in effluent water quality resulting from uncertainty in the system parameters is investigated. Also, improvement in the reliability of WTP using modified design parameters is investigated along with its cost implications. From the results, a method to calculate a set of safety factors corresponding to various performance reliability levels is proposed.     

Avoiding Change Orders in Public School Construction

Increased student enrollment and the current poor state of the educational infrastructure require the construction of more school buildings and the renovation of many of the existing ones. The large number and magnitude of change orders in these projects constitute an impediment to the rapid and economic delivery of these projects. A total of 6,585 change orders filed in a school district’s projects in the 5 1/2 year period from 1999 to 2004 were analyzed in five categories including owner-directed changes, code compliance issues, errors/omissions in contract documents, discovered or changed conditions, and others. The results of the study indicate that the dollar value of change orders relative to the original contract can be reduced if preventive measures are taken. These measures include choosing the right construction management firm, emphasizing the definition of project scope early in the project, and effectively managing the precontract activities by conducting value engineering and constructability reviews. The results indicate that school projects can be completed with change orders not exceeding 5% of the contract value if these measures are taken. This study is of relevance to practitioners involved in school design and construction projects.     

Framework of Success Criteria for Design/Build Projects

Success has always been the ultimate goal of every activity, and a construction project is no exception. Due to the ambiguous definition of project success and the different perceptions of participants toward this concept, it may be difficult to tell whether a project is successful as there is a lack of consensus. Time, cost, and quality have long been the success criteria used to evaluate the performance of a construction project. However, such a list has been criticized as not being comprehensive. Even studies of the project success of a particular construction method, such as the design/build procurement system, are lacking in most previous research considering construction projects in general. This paper sets out to establish criteria for project success for a design/build project in construction, first by identifying relevant measures of project success for a construction project in past studies, with particular emphasis on design/build projects, and then by establishing a comprehensive assessment framework for project success for design/build projects. The significant impacts on the construction field of study, in terms of educational value and practical use, are also presented. With little research in the project success of design/build projects, the writers suggest a research focus for the study.     

Quantitative Impacts of Project Change: Size Issues

Change has a tremendous effect on the performance of a construction project. Research that focuses on the quantitative impact is limited, incomplete, and in some cases questionable. The goals of this study were to quantify the nature and impacts of project change and develop recommended practices so that owners and contractors can manage change better. The focus was on project change during detailed design and construction, in particular the size of change and its impact on the project. These results show that the amount of change is negatively correlated with productivity and total installed project cost, whether within the design phase or construction phase, or between them. The greater the amount of change the more productivity and costs are degraded. Recommendations are also offered here on how to mitigate the impact of project change.     

Probabilistic Duration Estimation Model for High-Rise Structural Work

The duration of a construction project is a key factor to consider before starting a new project, as it can determine project success or failure. Despite the high level of uncertainty and risk involved in construction, current construction planning relies on traditional deterministic scheduling methods that cannot clearly ascertain the level of uncertainty involved in a project. This, subsequently, can prolong a project’s duration, particularly when that project is high-rise structural work, which is not yet a common project type in Korea. Indeed, among construction processes, structural work is notable, as it is basically performed outdoors. Thus, no matter how precisely a schedule is developed, such projects can easily fail due to unexpected events that are beyond the planner’s control, such as changes in weather conditions. Therefore, in this study, to cope with the uncertainties involved in high-rise building projects, a probabilistic duration estimation model is developed in which both weather conditions and work cycle time for unit work are considered to predict structural work duration. According to the proposed estimation model, weather variables are divided into two types: weather conditions that result in nonworking days and weather conditions that result in work productivity rate (WPR) change. Obtained from actual previous data, the WPR is used with relevant nonworking day weather conditions to modify the actual number of working days per calendar days. Furthermore, on the basis of previous research results, the cycle time of the unit work area is assumed to follow the β probability distribution function. Thus, the probabilistic duration model is valid for 95% probability. Finally, a case study is conducted that confirms the model can be practically used to estimate more reliable and applicable probabilistic durations of structural work. Indeed, this model can assist schedulers and site workers by alerting them, at the beginning of a project, to project uncertainties that specifically pertain to structural work and the weather. Thus, the proposed model can enable personnel to easily amend, and increase the reliability of, the construction schedule at hand.     

Collaborative Planning and Scheduling of Interrelated Design Changes

During the detailed design stage of a building project, a vast amount of mostly interrelated design information is generated and communicated among specialists from several disciplines. Changes in some design information are inevitable due to the iterative nature of the design process. In many cases, when the design of a building component is modified by one discipline, this change affects the design of many related building components that are the responsibility of several other design disciplines. Commitment and resources are needed to accommodate such design changes to maintain compatibility among all the design information. Otherwise, incompatibility errors become embedded in the design information leading to numerous problems during the construction of the project. This paper presents a computer-assisted methodology that helps design managers in planning and scheduling changes with interrelated effects on the design information.     

Renovation Projects: Design Process Problems and Improvement Mechanisms

This paper presents a case study of a recent office renovation project. The paper investigates the problems that occurred during the design process, analyzes the causes of design iterations and rework, and proposes changes that can improve the design process. The analysis illustrates two design challenges that cause iterations and rework: (1) preexisting, hidden conditions identified late in the design process, and (2) limitations of downstream systems that were not accounted for in upstream decisions. The recommendations propose mechanisms to reduce design rework and duration, and increase the quality of the design solution. The recommendations are (1) to accelerate the discovery of existing conditions, (2) to identify the project constraints that design and construction have to meet, (3) to select the project team early, and (4) to accelerate the iterative design process with a team-based rapid development of schematic design (rapid prototyping).