Study On The Dependence Of Duration In Project Scheduling Networks

In the practice of construction management, dependence between the duration variables of activities becomes very common, which may be caused by various objective or man-made factors. Currently, the requirement of construction project management becomes increasingly high, and demands for construction progress control also get more and more harsh. In the progress management of real construction projects, it is very important to consider the dependence between duration variables reasonably, which can be very helpful to estimate the uncertainty of construction period more adequately,forecast and assess risk more accurately, update the project schedule, and thus to control construction progress more efficiently. This dissertation, based on survey and analysis of dependence between duration variables, aims to construct graph models describing the dependence structure between duration variables, set up reasonable index system for dependence measurement, and study the problems of construction period and project schedule updating in view of dependence between activity durations. Main contents and details are listed below:Firstly, basic structure, randomness of activity durations and the independence assumption in classical CPM/PERT network models have been reviewed. Then based on the survey of multiple real construction projects, statistical analysis has been made on durations using dependence index, which indicated that there exists strong dependence between durations of parallel or serial activities. With surveying matters and questionnaires for experts, dependence between activity durations has been categorized systematically. The cause for such dependence has been analyzed, which turns out to be common factors and project organization and control.Secondly, through analyzing AON network plan and Bayesian network, a Bayesian Network Plan (BNP) model structure has been presented laying the AON network plan as background layer and considering parallel/serial dependence between duration variables, which can reasonably describe the dependence between duration variables. The separate and conditional independence in the model has also been discussed. In addition, methods for determining probability distribution of duration variables in BNP model has been introduced, and approaches for determining conditional probability between variables and parameter learning with reduced parameters and incomplete data has been studied.Thirdly, based on unique advantages of Copula function, Copula-function-based indexes for measuring dependence between durations and the methods to estimate such index in real projects have been presented, which has been done through analyzing advantages and disadvantages of liner correlation in measuring dependence between durations. Moreover, the properties and modes of general Copula functions when describing dependence between durations have been analyzed, and a mixed Copula function has been constructed to describe the dependence between duration variables with various dependence modes.Fourthly, basic steps of Monte Carlo simulation applied in construction period with dependent durations have been introduced. According to theoretical models and dependence measuring indexes mentioned above, approaches to generate random numbers and determine probability distribution of duration variables have been studied. A simple example has been given to demonstrate the simulating process, with the results compared with those from other models.Fifthly, methods for updating duration variables in BNP model have been introduced according to Bayesian Theorem and Bayesian Network Reasoning Theorem. Several methods including variable elimination, clique tree propagation and Markov chain Monte Carlo algorithm have been presented for the case that duration variables are discrete. In the situation with continuous or mixed variables, approaches for updating duration variables in BNP models and mixed BNP models have been studied and a numerical example has been given.At last, the application framework for applying the research results to the practice of construction project schedule management has been proposed, methods for determining and updating project schedule plan have been introduced when considering dependence between durations, and a real construction project has been taken as an example to illustrate the application. The results indicated that the approaches proposed in the dissertation have wide application prospect and fairly good value, because they can give more reasonable estimation to the uncertainty of schedule plan and update schedule plan dynamically according to the dependence between activity durations.