ONLINE CONTROL MODEL FOR NETWORK CONSTRUCTION PROJECTS

An activity-on-are network project of the PERT type with random activi ty durations is considered. For each activity, its accomplishment is m easured in percentages of the total project. When operated, each activ ity utilizes resources of a pregiven capacity and no resource realloca tion is undertaken in the course of the project's realization. Each ac tivity can be operated at several possible speeds that are subject to random disturbances and correspond to one and the same resource capaci ty; that is, these speeds depend only on the degree of intensity of th e project's realization. For example, in construction projects partial accomplishments are usually measured in percentages of the total proj ect, while different speeds correspond to different hours a day per wo rker. The number of possible speeds is common to all activities. For e ach activity, speeds are sorted in ascending order of their average va lues-namely speeds are indexed. It is assumed that at any moment t > 0 activities, in operation at that moment, have to apply speeds of one and the same index that actually determines the project's speed. The p rogress of the project can be evaluated only via inspection at control points that have to be determined. The project's due date and the cha nce constraint to meet the deadline are pregiven. An on-line control m odel is suggested that, at each control point, faces a stochastic opti mization problem. Two conflicting objectives are imbedded in the model : (1) to minimize the number of control points, and (2) to minimize th e average index of the project's speeds which can be changed only at a control point. At each routine control point, decision-making centers on determining the next control point and the new index of the speeds (for all activities to be operated) up to that point. The model's per formance is verified via simulation. The developed on-line control alg orithm can be used for various PERT network projects which can be real ized with different speeds, including construction projects and R&D pr ojects.