| The successful implementation of schedule management will directly affect the cost management and quality management of the project.Therefore,it is of great significance to do in-depth research to ensure that the project is completed as soon as possible under a certain completion probability for improving the economic benefits of the project.The program evaluation and review technique(PERT)in the traditional schedule management method can accurately reflect the real information of the process duration,and can be simulated by computer software,but the method does not consider resource constraints and human behavior.In order to remedy the shortcomings of PERT,the method of critical chain project management(CCPM)has been developed rapidly,but it is too optimistic to set the duration of process,and it is not easy to grasp the "key" of the project,and the preparation of a reasonable network schedule is the basis and the first step of schedule management.Therefore,the paper combines the unique advantages of the two methods,obtains the network schedule based on modified PERT,improves the key chain technology from key chain identification,buffer setting and buffer monitoring,so that it can be applied to the planning and implementation phases of the project at the same time.The main work of the paper is as follows:(1)In order to reflect the uncertainty of the process duration,the fuzzy Delphi method is used to estimate the duration of each process in the PERT network,and the variance adjustment factor is used to correct the variance calculation formula to improve the accuracy of the project expectation and variance.Considering the possibility of non-critical route and critical route transformation,the monte carlo simulation(MCS)method is used to simulate them,and the critical route of the PERT network are identified based on the obtained sensitivity indicators and the criticality of each process is determined.(2)In order to solve the problem of resource constraints in engineering projects,the sequential couple theory is introduced,and the priority of parallel processes in resource conflicts is adjusted based on the improved gravity method to determine the critical chain,so as to achieve the optimization goal of resource constraints and shortest time limit.(3)The triangular fuzzy number in the fuzzy theory is used to estimate the safety time,and the influence of internal and external factors on the project schedule is considered comprehensively.Based on the root variance method,the calculation formula of buffer size is improved to make the buffer setting more reasonable.In order to improve the guarantee rate of project completion on time,fully consider the dynamic change characteristics of uncertainties faced by the project,allocate the total amount of buffer based on risk weight factor and dynamically allocate the residual buffer at the monitoring point in real time,so as to realize the dynamic adjustment of the monitoring trigger point,and use the sensitivity index obtained by simulation to set up the monitoring trigger point.The monitoring threshold is used to realize the dynamic buffer monitoring model based on sensitivity index.The critical chain schedule management model based on modified PERT established in this paper reasonably combines the advantages of both,effectively improves the defects of the original schedule management method,and provides a basis for managers to better guide the project construction. |
