Research On Risk Calculation In Project Schedule

In the control of construction schedule for Hydropower Projects,risk analysis of the schedule is a key. In this paper,Monte Carlo(MC) method is used in the Research of distributing of construction duration and computation of time parameter of PERT network. According to probability viewpoint,critical line and key degree of activity in the network are also defined. Aiming at the limitation of application of the MC in large scale the network,the simplified computational method for the network is presented with quantum probability theory and composite method of path in network. According to the characteristic of precedence network of Hydropower Projects,it is transferred into generalized PERT network,as well the computation of schedule risk is discussed. The achievements achieved in the study are presented as follows:(l)To the distribution of construction duration of the PERT network,even though every activity duration obeys normal distribution,it is failed to be proved to be in the obedience with normal distribution strictly. However,if there -are a lot of activities in a path of the PERT network,for instance,more than 20 activities,without reference to the normal distributions-distribution or triangle distribution which activities duration obeys,the construction duration approximately obeys the normal distribution when the form of distribution is not partiality seriously. (2)After the concept of critical rate is used,critical path is decided with the help of MC.The computational risk of schedule is comparably small with the classical PERT method,but it is effective to decide the critical path-method.(3)With the conception of quantum probability and composite method of path in network,the earliest time of node merged with two or more paths is corrected,and then make a dummy activity which follows the node and which holds a durationtime that the earliest time of the node added time after the paths are merged,and the subsequent work of the node follow the dummy activity. Compared with the MC method,the modified PERT method has comparably computational precision. (4)Substitute the every precedence relation of precedence construction network with a procedure,and the lag of precedence relation is defined as duration of the procedure which is named as lag procedure. The lag procedure does not consume resource,and the duration is random or determined. After the lag procedure introduced,the precedence network is transferred into generalized PERT network,and then the risk of construction schedule could be calculated with the MC method or the modified PERT method.