Linear Scheduling Optimization Model for Planning Repetitive Construction Projects

Scheduling of repetitive construction projects is more complex and challenging due to large number of decision variables, constraints, and tradeoffs between time and cost. Traditional time-driven scheduling techniques such as critical path method (CPM) are inefficient in scheduling repetitive construction projects since they do not maintain crew work continuity. The present study focuses on developing an exact linear optimization model for scheduling repetitive construction projects with multiple crews and multiple options of construction methods for each activity. The optimization model is developed in three steps: (1) identifying decision variables; (2) formulating objective function and constraints; and (3) implementing model computations. Decision variables are identified to model start time of each activity at each unit, number of crews, idle time of crews, and construction methods. The objective function is designed to minimize the project total cost including the direct cost of activities, cost of additional crews for activities, and idle cost of crews during the entire project. Additionally, several constraints are integrated in the model to ensure practicality of the identified solution. Finally, the model computations are executed using the problem-based optimization modeling of MATLAB 2019a and mixed integer linear programming (MILP) solver in Gurobi. The performance of the developed model and its capabilities were tested on a case study of 100 repetitive units with nine activities to complete each unit. The optimization model identified the optimal schedule of the project while complying with specified duration. The results show the developed optimization model is capable of identifying optimal schedule of repetitive projects that can lead to minimum project cost while maintaining crew work continuity.