Optimized planning approach for multiple tower cranes and material supply points using mixed-integer programming

It is common to implement multiple tower cranes on building construction projects. The plan for usage of multiple tower cranes should be optimized for better project performance, such as reduced cost or operation time. Optimization of plans for multiple cranes is complex, especially when considering the supply of transported material (e.g., location, quantity, material type), as well as assigning lift tasks among tower cranes that are in range. This study developed a mathematic formulation that can solve this optimization problem using mixed-integer programming. The formulation introduces several binary variables and restricts the domain of the indices of these variables using an additional set of auxiliary variables. The proposed model contributes to the body of knowledge by showing the feasibility of using mixed-integer-programming techniques to solve the optimization problem of multiple tower cranes and their supply systems. The findings also demonstrate that when a multiple tower crane problem is concerned, optimizing each piece of equipment individually could lead to suboptimal solutions. Specifically, the operation time drops by 6.8% and the operation cost decreases by 3.6% in the two-tower crane case study example. The proposed model can also assist engineers with assessing a large number of alternative plans, which are heavily needed in preconstruction planning, where site layout is preliminary.