Research On Time-Cost Tradeoff Problem Based On Properties Of Network

With the development of economic development, project management is becoming more and more important. The three major objectives of project management are the time, cost and quality management. Time and cost management are related to each other. The comprehensive optimization of time and cost, namely the time-cost optimization problem is very important in project management, which is of great significance in theory and practice. Many methods to solve time-cost tradeoff problem have been designed. This paper mainly studies how to solve the time-cost tradeoff problem effectively by using properties of CPM network planning fully, particularly properties and laws of float. The research on time-cost tradeoff problem started from the early1960s and the relative scope has expanded a lot in the following decades. However, no breakthrough has been made with regard to the solution of the problem. The main bottleneck is the high complexity and huge work load of computation involved in solving this kind of problem.In order to get rid of the bottleck, another way of thinking is introduced in this paper, namely, to simplify the target rather than to seek and improve the algorithm. By using CPM network planning technique as the tool, this paper studied the properties of float. Based on the above properties, the super-large type project network is simplified as an equivalent simple network, making the incomputable and complex problem a computable and easy one. What is particular is that the work load of computation of the simplified network is largely reduced whatever agrithorm is used. Therefore, the study made in this paper is not only of therotical significance but also of great practical value.Except for the equivalent simplification, this paper use another two approaches to simplify the time-cost tradeoff problem, the one is to define the maximal and effective compression of each step, and the other is to modify the compression of each activity duration. For defining the maximal and effective compression of each step, the objective is to realize the most effective compression of the project duration by using the fewest compressing steps. The principle is that, in one compression step and compressing the critical prath in the network, the compression should stop when new critical paths appear, and then the compression value now is the maximal and effective compression of the step. For modifying the compression of each activity duration, it mainly bases on a basic principle of global optimization, that is, the optimization of each step is not equal to the optimization of the global process. Even if the compression cost in each step is minimum, and the compression is the maximal and effective one, then the finial compression effect may not the optimal, even may be the worst. Therefore, in order to realize the optimal compression, we need to modify the compression of each activity. The main principle of modifying compression is that, if the compression of a critical activity is the optimal, then it will still be a critical one after compression; and if it becomes a non-critical one after compression, then the compression must not be the optimal, and now it need to be modified that, prolong duration of the activity until it becomes a critical one again.The main study in this paper is detailed as follows:1. This paper extends the classical critical path method. The classcal critical path method could be used to define advisable bound of each activity’s time parameter. Time parameter of each activity dose not have strict restriction itself commonly, but is restricted by total duration and other activities, which could be represented by using critical path method. But if time parameters of several activities having some restrictions themselves, such as fixed start time or terminate time, then what changes may happen on time parameters of other activities under this affection. Under this condition classical critical path method is usefully to solve. Therefore, this paper analyzes the problem, and designs extend critical path method to confine advisable bound of time parameter.2. The widely method to solve time-cost tradeoff problem is network flow algorithm with CPM network at present. The algorithm has a certain degree excellence, but also has clear fault. This paper aims at the excellence and fault, analyzes how to improve for advancing solved effect and correctness of orginal method, and gave improved theory.3. This paper designs improved direct algorithm to solve time-cost tradeoff problem. According to improved theory of direct algorithm, gives improved measures, for example, gives new method to simplify time-cost tradeoff peoblem equivalently, gives the maximum and effective quantity of compressing duration in each compressing step, and amends quantity of compressing duration reasonably, etc. and then designs two improved methods of direct algorithm by using these measures.4. This paper designs new algorithm to solve continuous time-cost tradeoff problem. According to improved theory and idea, the paper analyzes the time-cost tradeoff problem from new idea, and designs new idea and method.