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Project Schedule Development under Environment-Induced Time-Window Constraints: Case of Constructing River-Crossing Bridge in Remote Northern Region
... While the start time of the project is random, and some activities in the project can't be carried out in certain time periods, which may affect the overall progress of the project. For example, there are environmental work windows in dredging fleet scheduling [20], weather windows in offshore operation [21], and special time windows in water conservancy construction, additionally, the project is affected by seasonal conditions and environmental regulations [22]. For example, the construction of river dikes and channels, which usually lasts for more than one year, is subject to seasonal flooding. ...
Water conservancy project scheduling is an extension to the classic resource-constrained project scheduling problem (RCPSP). It is limited by special time constraints called “forbidden time windows” during which certain activities cannot be executed. To address this issue, a specific RCPSP model is proposed, and an approach is designated for it which incorporates both a priority rule-based heuristic algorithm to obtain an acceptable solution, and a hybrid genetic algorithm to further improve the quality of the solution. In the genetic algorithm, we introduce a new crossover operator for the forbidden time window and adopt double justification and elitism strategies. Finally, we conduct simulated experiments on a project scheduling problem library to compare the proposed algorithm with other priority-rule based heuristics, and the results demonstrate the superiority of our algorithm.
Purpose
Construction projects are complex projects taking place in dynamic environments, which necessitates accounting for different uncertainties during the planning stage. There is a significant lack of management tools for repetitive projects accounting for uncertainties in the construction environment. The purpose of this paper is to present an algorithm for the optimized scheduling of repetitive construction projects under uncertainty.
Design/methodology/approach
Fuzzy set theory is utilized to model uncertainties associated with various input parameters. The developed algorithm has two main components: optimization component and buffering component. The optimization component presents a dynamic programming approach that processes fuzzy numbers. The buffering component converts the optimized fuzzy schedule into a deterministic schedule and inserts time buffers to protect the schedule against anticipated delays. Agreement Index (AI) is used to capture the user’s desired level of confidence in the produced schedule while sizing buffers. The algorithm is capable of optimizing for cost or time objectives. An example project drawn from literature is analysed to demonstrate the capabilities of the developed algorithm and to allow comparison of results to those previously generated.
Findings
Testing the algorithm revealed several findings. Fuzzy numbers can be utilized to capture uncertainty in various inputs without the need for historical data. The modified algorithm is capable of optimizing schedules, for different objectives, under uncertainty. Finally AI can be used to capture users’ desired confidence in the final schedule.
Originality/value
Project planners can utilize this algorithm to optimize repetitive projects schedules, while modelling uncertainty in different input parameters, without the need for relevant historical data.
The classic critical path method (CPM) determines total float (TF) for each individual activity by performing forward pass and backward pass analyses. A comprehensive literature review has shown that TF is the most crucial attribute of a scheduled activity, and plays a fundamental part in advanced scheduling research. This research proposes a simplified version of CPM, called path-float-based critical path method (PFCPM), which determines TF based on identification of path float (PF) instead of entailing a backward pass analysis in the classic CPM. Analytical proof is provided and step-by-step application procedures are generalized. Then, PFCPM application examples are given based on two demonstration projects represented in activity-on-node (AON) and precedence diagram method (PDM) networking formats, respectively. Results are compared with the classic CPM for cross-validation. The newly proposed PFCPM enhances CPM-based scheduling through circumventing the backward pass analysis in deriving TF based on PF; helping researchers and practitioners interpret the TF ownership issue and account for changes on TF as a result of activity delay by relating TF with PF; and laying a theoretical foundation for further research into advanced construction planning methods such as resource loading, time–cost tradeoff and risk analysis.
The Australian construction industry has similar characteristics to many construction industries around the world. However, Australia's construction industry needs to service a country with a large percentage of remote and isolated areas. These remote and isolated areas have recently seen major demand for construction works in a large part due to the current resources boom. Remote construction projects introduce many challenges not witnessed in urbanized locations. Therefore, this research aims to identify the main challenges facing Australian construction contractors in remote locations. Construction projects in general are complex and require a high degree of management. In remote areas this is seen as being intensified. Hence, this research sets out to highlight the contributing factors to the problem. It surveyed industry practitioners in relation to construction in remote areas. Likert and ranking scale methods were used in questionnaires with 75 returned. The results were analysed and discussed based on measuring collective participant response to the issues. The findings confirmed that there are major challenges associated with remote construction activity. Significant issues were found to reside within the areas of human resources, production, cost management, infrastructure and communications. Some reasoning of issues and courses of action were also offered. Remote construction activity within Australia is expected to further increase in coming years so it is hoped that the findings will be useful to industry practitioners. Whilst the research is based within the Australian construction industry the findings are thought to relate to other countries and industries facing similar challenges in the geographical context.
In this paper we propose a new methodology for project control under uncertainty. In particular, we integrate Earned Value Methodology (EVM) with project risk analysis. The methodology helps project managers to know whether the project deviations from planned values are within the “expected” deviations derived from activity planned variability. Although the methodology is new and innovative, we only go back to the fundamentals of project simulation to generate the “universe” of possible projects, according to the assumed variability of project activities. Then we organize and gather the information in order to make the data coherent with EVM. We explain the steps to implement the methodology and we show three case studies. The methodology makes explicit that the schedule and budget resulting from traditional methods like PERT are statistically very optimistic.
In this paper, a practical method is developed in an attempt to address the fundamental matters and limitations of existing methods for critical-path method CPM based resource scheduling, which are identified by reviewing the prior research in resource-constrained CPM scheduling and repetitive scheduling. The proposed method is called the resource-activity critical-path method RACPM, in which 1 the dimension of resource in addition to activity and time is highlighted in project scheduling to seamlessly synchronize activity planning and resource planning; 2 the start/finish times and the floats are defined as resource-activity attributes based on the resource-technology combined precedence relationships; and 3 the ''resource critical'' issue that has long baffled the construction industry is clarified. The RACPM is applied to an example problem taken from the literature for illustrating the algorithm and comparing it with the existing method. A sample application of the proposed RACPM for planning a footbridge construction project is also given to demonstrate that practitioners can readily interpret and utilize a RACPM schedule by relating the RACPM to the classic CPM. The RACPM provides schedulers with a convenient vehicle for seamlessly integrating the technology/process perspective with the resource use perspective in construction planning. The effect on the project duration and activity floats of varied resource availability can be studied through running RACPM on different scenarios of resources. This potentially leads to an integrated scheduling and cost estimating process that will produce realistic schedules, estimates, and control budgets for construction.
In the face of the high variability in the completion of construction projects, the following research is generated. In the literature we can find several proposals to program projects, however, the variability of the activities causes high variability in the completion date of the projects. We hope that the proposed method, by controlling the start of activities, will ensure the completion date of the projects, by fixing the start of every activity with a high level of probabilistic confidence for the planned project duration. The proposed fixed start method (FSM) was tested in two case studies by using discrete event simulation. Project completion duration results were compared with the critical path method (CPM) and the program evaluation and review technique (PERT). Project completion was evaluated in the case studies by the coefficient of variance (COV), mean, and variance. The new method decreased the scheduled duration variability while meeting project completion times.
A complex construction program usually consists of a group of interrelated projects with different levels of importance and degrees of certainty. Currently, time management of a construction program uses the same techniques as those for a single project, and the most commonly used technique is the critical path method (CPM). However, the CPM method lacks flexibility in handling uncertainties and options, a desirable feature in managing complex programs. This paper proposes a new scheduling method that is drawn from the authors' experiences of managing a large-scale construction program - the Shanghai Expo facility construction. The new method is developed on the basis of the traditional CPM method but is able to incorporate options and importance levels into the program schedule. The theoretical basis and calculation method of this new scheduling technique are discussed in the context of managing the Shanghai Expo facility construction program. This paper contributes to the body of knowledge in construction management by developing a new scheduling technique with proven applications.
Activity production rates drive the development and accuracy of linear schedules. The nature of linear projects dictates an assortment of variables that affect each activity's production rate. The purpose of this research was to expand the capabilities of linear scheduling to account for variance in production rates when and where the variance occurs and to enhance the visual capabilities of linear scheduling. This new linear scheduling model, a linear scheduling model with varying production rates (LSMVPR), has two objectives. The first is to outline a framework to apply changes in production rates when and where they occur along the horizontal alignment of the project. The second objective is to illustrate the difficulty or ease of construction through the time-location chart. This research showed that the changes in production rates because of time and location can be modeled for use in predicting future construction projects. Using the concept of working windows, LSMVPR allows the scheduler to develop schedule durations on the basis of minimal project information. The model also allows the scheduler to analyze the impact of various routes or start dates for construction and the corresponding impact on the schedule. The graphical format allows the construction team to visualize the obstacles in the project when and where they occur by using a new feature called the activity performance index (API). This index is used to shade the linear scheduling chart by time and location with the variation in color indicating the variance in predicted production rate from the desired production rate.
Many projects, such as the construction of roadways, pipelines, and high-rise buildings, involve repetitive activities. A method for scheduling such work, the Linear Scheduling Method (LSM) is presented. In an LSM schedule, the repetitive activities are plotted as lines of constant or varying slopes on two axes, distance versus time. Discrete activities may be shown at their appropriate times and locations and then referenced to a network schedule for additional detail. The Linear Scheduling Method is illustrated by applying it to an actual roadway construction project. The simplicity of the system and advantages for certain types of projects are revealed. A sample schedule is used to derive information that is comparable to what may be obtained from an equivalent CPM network.
Among the major problems facing technical management today are those involving the coordination of many diverse activities toward a common goal. In a large engineering project, for example, almost all the engineering and craft skills are involved as well as the functions represented by research, development, design, procurement, construction, vendors, fabricators and the customer. Management must devise plans which will tell with as much accuracy as possible how the efforts of the people representing these functions should be directed toward the project's completion. In order to devise such plans and implement them, management must be able to collect pertinent information to accomplish the following tasks: (1) To form a basis for prediction and planning (2) To evaluate alternative plans for accomplishing the objective (3) To check progress against current plans and objectives, and (4) To form a basis for obtaining the facts so that decisions can be made and the job can be done.
The author presents a condensed exposition of some basic ideas underlying fuzzy logic and describes some representative applications. He covers basic principles; meaning representation and inference; basic rules of inference; and the linguistic variable and its application to fuzzy control.< >
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