A Computer-Aided Heuristic Model for Determining Cost-Time Trade-offs in Building Construction (1987) 

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Alaattin Kanoglu

ITU Faculty of Architecture

Division of Construction Management

Prof.Dr. Yildiz Sey, Supervisor

The aim of this study is to emphasize the relation which is known to exist between the time and cost of projects, to determine the principles of this relation and a Computer-Aided model for determining optimum project completion time. The model first of all takes the normal times of activities which form the network of project and then calculate earliest and latest start and finish dates of the activities by using the Critical Path Computer Program developed for the model. 

After determining the critical path, the model begin to contract the network. As it is known, the completion time is determined by critical activities. For this reason in order to shorten the time, this activities must be speeded up. But even a medium sized network there are lots of activities which are not necessary to add into calculation. It is possible to eliminate these critical activities. For this purpose a heuristic elimination method has been developed in this study. 

This method is one of the main points of the model. According to this method some "lines" and "representatives" of these lines are defined in the model. If the number of activities are more than one, then the critical activity which has the lowest "slope" is chosen as the "representative" of the line and the others are left aside until it is not possible to speed up the activity which represents the line. In order to shorten the duration of project the representative(s) of the critical path(s) must be speeded up. The algorithm determines all the alternative sets of representative activities which contracts the network and their costs sistematically. Since the algorithm sorts every alternative which comprises of 1,2,3…n activities regarding to their costs it eliminates some alternatives for every group exceeding the last accepted set having the minimum cost increase. 

The model suggest a new heuristic approach to solve the problem of determining the completion time of project with minimum cost. There are a number of analog (electrical circuits etc.) and mathematical models (linear programming etc.) to solve the problem. The algorithm developed within the study use the power of computer and eliminates the difficulties of the others in which the problem solver has to undertake the main role instead of computer. The algorithm is not suitable for manual operation and may not be evaluated as a successful model but it becomes reasonable and preferable by utilizing the strength of a computer in speed, repetition etc.