Developing a time-cost trading-off model for construction projects in fuzzy environment (case study: weigh in motion system)

Completion time is an important issue on construction projects with limited practical duration usually studied comparing to construction or implementation cost. In this research work, the fuzzy behaviour of cost and time for project activities has been investigated based on predicted completion time followed by developing a mathematical model for making a trade-off approach for project planning. The objective function is to minimise project cost which is defined in discrete and continuous domains considering limited implementation time. According to the constraints, a nonlinear model was developed, so a linearisation technique has been utilised to convert that to linear. In addition, an acceptable range of changes (tolerance) is considered for the project completion time to achieve better solutions followed by making a sensitivity analysis process on results of time-cost trading-off approach. Installing a weigh in motion (WIM) system in the central Iranian road of Isfahan-Naein has been selected as case study and the proposed model has been validated using experimental data. Results revealed that the proposed model, which has been converted to linear, is capable to perform a time-cost trading-off approach for projects of those that do not have exact time and cost for project activities.